A study on energy efficiency in system development...

Master of Science Thesis KTH School of Industrial Engineering and Management

Energy Technology EGI-2017-0024 MSC Division of Applied Thermodynamics and Refrigeration

SE-100 44 STOCKHOLM

A study on energy efficiency in system development environments and related

equipment

Nevin Gürsoy

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Master of Science Thesis EGI 2017-0024 MSC

A study on energy efficiency in system development environments and related

equipment

Nevin Gürsoy

Approved

Date

Examiner

Joachim Claesson

Supervisor

Jörgen Wallin Commissioner

Saab AB

Contact person

Peter Myrbäck

Abstract The modern society and its basic functions are dependent on different type of energy carriers. The usage of electronic appliances and computers in particular, has varying impact on energy usage, which in turn influence the performance of the cooling systems and the experienced thermal climate conditions in buildings. This study analyzes the energy usage within system development environments at Saab facility in Järfälla. The work process was divided in two parts; identifying the current energy consumption level in the system development environments and investigating potential energy efficiency measures that can be implemented. An evaluation on the defined energy systems showed that computer labs and related equipment as well as components associated with the cooling system used 64 % of the total energy demand in D building at Saab´s facility. Based on these results, several energy efficiency measures are proposed that would have significant potential to reduce the current energy usage and generate economic savings with low or no impact on the business activities and indoor thermal conditions. One of the most important findings was that the usage patterns of computers and monitors have a considerable contribution to the heat loads. It was shown that improved power management in computers placed in the system development environment could decrease the total energy consumption of cooling and electricity by 569 MWh per year. A final analysis emphasizes the importance of the location of the system development environments, as this factor is highly significant for an efficient reduction of the cooling demand in the existing building.

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Sammanfattning Det moderna samhället och dess grundläggande funktioner är beroende av diverse energibärare. Användning av elektroniska utrustningar och i synnerhet datorer kan ha varierande effekter på energianvändning, vilket i sin tur påverkar performansen av kylsystem och det upplevda termiska klimatet i byggnader. Denna studie har som mål att undersöka energianvändningen inom systemutvecklingsmiljöer på Saab AB i Järfälla. Arbetet utfördes genom två etapper: identifiering av det nuvarande energibehovet inom systemutvecklingsmiljöer och att analysera de potentiella energieffektiviserande åtgärderna. Utvärderingen av energisystemet visade att energibehovet i datalabbar och relaterad utrustning samt de associerade kylsystem komponenter utgör i dagsläge 64 % av de totala elektricitetskostnaderna i D huset på Saab fastighet i Järfälla. Baserad på detta resultat, ett antal energieffektiviseringsåtgärder som kan minska the nuvarande energiförbrukningen och kostnader föreslogs, vilka förväntas att inte ge påtagliga effekter på affärsverksamheten och inomhus klimatet. Användningsmönstren av datorer och skärmar visade sig att ha en betydande påverkan på värmebelastningen i dessa miljöer. Beräkningarna visade att installera energisparlägen utanför arbetstiderna i datorer placerade i systemutvecklingsmiljöer kan minska den totala energianvändningen för kyla och el med 569 MWh per år. En slutlig analys betonar vikten av placeringen av systemutvecklingsmiljöerna, vilket är en signifikant faktor för en effektiv minskning av kylbehovet i den befintliga byggnaden.

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Acknowledgement This master thesis is written at the Royal Institute of Technology (KTH) and conducted in cooperation with Saab AB in Järfälla during the spring of 2017.

Initially, I would like to thank everyone that in one way or another have contributed to form this master thesis. I would like to send my greatest thanks to my supervisor Jörgen Wallin at KTH, Lars Malm and Peter Myrbäck at Saab for giving me the opportunity of performing this master thesis but also for their support, encouragements, and guidance during this process.

Also thanks to all the members of Coor Service Management for the help with measurements and inputs regarding technical system at the facility. I would also like to thank Christer Pettersson and Johnny Westergren for the help with a number of measurements and spared some time to answer my questions.

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Abbreviations

AHU Air handling Unite

Boverket National Board of Housing, Building and Planning

CAV Constant –volume system

CFC Chlorofluorocarbons

COP The coefficient of performance

CRAC Computer room air conditioner

CO2 Carbon Dioxide

EIA U.S. Energy Information Administration

EU European Union

FCU Fan coil unit

GHG Greenhouse Gas

HCFC Hydro chlorofluorocarbons

HFC Hydro fluorocarbons

HVAC Heating, Ventilation and Air conditioning

OECD Organization for Economic Co-operation and Development

OVK Obligatory ventilation control

SEK Swedish crown

VAV Variable-volume system

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Nomenclature 𝑎 The sum of the annual incomes [SEK/year]

𝑎!"#$%&$"$'& Annual maintenance costs [SEK/year]

𝐶!"!#$% Net present value of energy costs [SEK]

𝐶!"#$%&'$"& Net present value of initial investments [SEK]

𝐶!"#$%&$"$'& Net present value of maintenance costs [SEK]

𝐶!"#$%&'( !"#$% Net present value of equipment final year [SEK]

𝐶! Specific heat capacity [J/kg*K]

𝐶𝑂𝑃! Coefficient of Performance of the refrigerant cycle [-]

𝑒!"!#$% Current energy price [SEK/kWh]

𝐸 Necessary operating energy [W]

𝐸!"!#$% Annual energy requirement [kWh/year]

𝐸! Power required for the pump [W]

𝑖 Rate of discount [%]

𝑘 The sum of the annual running costs [SEK/year]

𝐼 Current [A]

𝐿𝐶𝐶!"!#$ Total life cycle costs [SEK]

𝑚 Mass flow of the fluid [kg/s]

𝑛 Years of operation [year]

𝑁 Change in speed [rpm]

PP Payback period [year]

𝑝! Pressure at the inlet of the pump, [Pa]

𝑝! Pressure at the outlet of the pump [Pa]

𝑞 Annual increase in energy price [%]

𝑄 Change in volume [l/s]

𝑄 Effect [kW]

𝑄! Useful refrigeration power [W]

T The initial investment [SEK]

𝑉 Voltage [V]

𝑉 Volumetric flow [m3/s]

𝜌 Density of the fluid [kg/m3]

cos𝜑 Power factor [-]

∆𝑝 Change in pressure [Pa]

𝜂! Total pump efficiency [-]

𝜂!"# Efficiency of heat exchanger [-]

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Table of Contents Abstract ........................................................................................................................................................................... 2

Sammanfattning ............................................................................................................................................................. 3

Acknowledgement ........................................................................................................................................................ 4

Nomenclature ................................................................................................................................................................ 6

Index of Figures ......................................................................................................................................................... 11

Index of Tables ........................................................................................................................................................... 12

1 Introduction ............................................................................................................................................................. 14

1.1 Background ................................................................................................................................................. 15

1.2 Aim and Objective ..................................................................................................................................... 16

1.3 Method ......................................................................................................................................................... 16

1.4 Limitations .................................................................................................................................................. 17

2 Company presentation – Saab AB in Järfälla ..................................................................................................... 18

2.1 Overview of the D building ..................................................................................................................... 19

2.2 Previous studies .......................................................................................................................................... 19

2.3 Current energy situation ............................................................................................................................ 19

3. Literature review .................................................................................................................................................... 22

3.1 HVAC systems ........................................................................................................................................... 22

3.1.1 All-air-systems ..................................................................................................................................... 22

3.1.2 Air- and water systems ....................................................................................................................... 24

3.1.3 All-water systems ................................................................................................................................ 25

3.2 Cooling systems .......................................................................................................................................... 25

3.2.1 Vapour compression cycle ................................................................................................................ 25

3.2.2 Components and configurations ...................................................................................................... 26

3.3 Cooling distribution systems .................................................................................................................... 29

3.3.1 Fan coils units ..................................................................................................................................... 30

3.3.2 Chilled baffles ..................................................................................................................................... 30

3.3.3 Computer room air conditioner (CRAC) ....................................................................................... 31

3.4 Control systems .......................................................................................................................................... 32

3.4.1 Pumps ................................................................................................................................................... 32

4 Methodology ....................................................................................................................................................... 33

4.1 Methodology overview .............................................................................................................................. 33

4.2 Existing energy system .............................................................................................................................. 33

4.3 Energy system boundaries ........................................................................................................................ 34

5 Calculation methods ........................................................................................................................................... 36

5.1 Refrigeration capacity ................................................................................................................................ 36

5.2 Pumps and volume flow rate ................................................................................................................... 36

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5.3 Affinity laws ................................................................................................................................................ 37

5.4 Power draw ................................................................................................................................................. 37

5.5 Cooling and heating in the AHUs ........................................................................................................... 38

5.6 The economic model ................................................................................................................................. 39

5.6.1 Payback period .................................................................................................................................... 39

5.6.2 Life cycle cost (LCC) ......................................................................................................................... 39

6 Energy mapping ...................................................................................................................................................... 41

6.1 Electricity survey ........................................................................................................................................ 41

6.1.1 Computer labs ..................................................................................................................................... 41

6.1.2 Fan coils ............................................................................................................................................... 43

6.1.3 Cooling units in computer labs ........................................................................................................ 43

6.1.4 Server rooms ....................................................................................................................................... 44

6.1.5 Pumps ................................................................................................................................................... 46

6.1.6 Ventilation ........................................................................................................................................... 47

6.2 Refrigeration power ................................................................................................................................... 48

6.2.1 The cooling system ............................................................................................................................. 48

6.2.2 The cooling demand .......................................................................................................................... 49

6.2.3 Cooling demand of the fan coils ...................................................................................................... 49

6.2.4 Cooling demand in the server rooms .............................................................................................. 50

6.2.5 Cooling demand in the computer labs ............................................................................................ 51

6.2.6 Cooling demand in the AHUs .......................................................................................................... 51

6.3 Chillers ......................................................................................................................................................... 51

6.3 Result of the energy mapping .................................................................................................................. 53

6.3.1 The electricity demand ....................................................................................................................... 54

6.3.2 Cooling requirements ......................................................................................................................... 55

7 Energy measures ................................................................................................................................................. 57

7.1 Switch of the screens and computers during night ................................................................................... 57

7.1.1 Cost ....................................................................................................................................................... 58

7.1.2 New energy demand .......................................................................................................................... 58

7.1.3 Result .................................................................................................................................................... 58

7.1.4 Discussion ............................................................................................................................................ 60

7.2 Installing new fan coils in the computer rooms ........................................................................................ 61

7.2.1 Costs ..................................................................................................................................................... 62

7.2.2 New energy demand ............................................................................................................................... 63

7.2.3 Result .................................................................................................................................................... 64

7.2.4 Discussion ............................................................................................................................................ 64

7.3 Lower the set point of supply air temperature in AHUs ..................................................................... 65

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7.3.1 Cost ....................................................................................................................................................... 65


7.3.3 Result .................................................................................................................................................... 66

7.3.4 Discussion ............................................................................................................................................ 66

7.4 Night cooling .............................................................................................................................................. 66

7.4.1 Cost ....................................................................................................................................................... 66


7.4.3 Result .................................................................................................................................................... 68

7.4.4 Discussion ............................................................................................................................................ 68

7.5 Demand controlled cooling in computer labs ....................................................................................... 69

7.5.1 Cost ....................................................................................................................................................... 69


7.5.3 Result .................................................................................................................................................... 69

7.5.4 Discussion ............................................................................................................................................ 70

7.6 Installing a separate AHU for computer labs ........................................................................................ 70

7.6.1 Costs ..................................................................................................................................................... 70


7.6.3 Result .................................................................................................................................................... 71

7.6.4 Discussion ............................................................................................................................................ 72

7.7 Change the location of the computer labs ............................................................................................. 72

7.7.1 Cost ....................................................................................................................................................... 73


7.7.3 Result .................................................................................................................................................... 75

7.7.4 Discussion ............................................................................................................................................ 75

7.8 Power saving states in personal computers ........................................................................................... 75

7.8.1 Cost ....................................................................................................................................................... 76


7.8.3 Result .................................................................................................................................................... 77

7.8.4 Discussion ............................................................................................................................................ 77

7.9 Improving the lighting system in server rooms ..................................................................................... 77

7.9.1 Cost ....................................................................................................................................................... 78


7.9.3 Result .................................................................................................................................................... 78

7.9.4 Discussion ............................................................................................................................................ 78

8 Discussion ................................................................................................................................................................ 80

8.2 Sensitivity analysis ...................................................................................................................................... 82

8.1.1 Cooling demand in computer labs ................................................................................................... 82

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8.1.2 Volumetric flow rate .......................................................................................................................... 83

8.1.3 Cooling units ....................................................................................................................................... 83

8.1.4 Default power saving state ................................................................................................................ 83

9 Conclusions ............................................................................................................................................................. 84

10 Future studies ........................................................................................................................................................ 85

Bibliography ................................................................................................................................................................ 86

Appendix 1 .................................................................................................................................................................. 90

Appendix 2 .................................................................................................................................................................. 91

Appendix 3 .................................................................................................................................................................. 92

Appendix 4 .................................................................................................................................................................. 93

Appendix 5 .................................................................................................................................................................. 94

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Index of Figures Figure 1: The Saab facility in Järfäla. ........................................................................................................ 18 Figure 2: The measured power consumption in D building during 2-13 March in 2017. ............... 20 Figure 3: Configuration of VAV air water systems (Claesson, 2016). ................................................ 24 Figure 4: Vapour compression cycle and the main components (Bright hub engineering, 2016). 26 Figure 5: Basic configuration of a vertical fan coil ( Claesson, 2016a). .............................................. 30 Figure 6: Typical "raised floor" cooled server room (Jonsson, 2009) ............................................... 32 Figure 7: A schematic overview of the existing energy system configuration and related

subsystems in D building. ................................................................................................................. 34 Figure 8: The measured power needed in a computer lab during one week in March. ................... 42 Figure 9: The measured power supply in a computer lab during one week in March. .................... 42 Figure 10: The power needed to an active cooling unit in a server room logged during one day. 46 Figure 11: Description of the system configuration of the cooling system and associated chilled

water loops. ......................................................................................................................................... 49 Figure 12: The measured power input to the chiller, VKA02, during 8 days. .................................. 52 Figure 13: The refrigeration power as function of ambient temperature. ......................................... 53 Figure 14: The variation of the cooling demand as a function of the average ambient temperature.

.............................................................................................................................................................. 53 Figure 15: The energy consumption share between different components that are defined in the

system boundaries. ............................................................................................................................. 55 Figure 16: Energy consumption level with changed power settings in computers in system

development environments. Along with the power reduction of the computers, the total energy usage for cooling demand is categorized for different power setting options. ........... 60

Figure 17: The temperature of the supplied ventilation air from LBA02 in D building. ................ 61 Figure 18: The logged indoor temperature in computer rooms. ......................................................... 61 Figure 19: The logged indoor temperature in 3 different offices during 8 days. .............................. 73 Figure 20: Impact on the refrigeration power in relation to the ambient temperature in computer

labs. ...................................................................................................................................................... 82 Figure 21: Sensitivity analyses on the cooling demand with changed ambient temperature

compared to climate independent cooling. The energy consumption is shown for the yearly electricity consumption for chillers, pumps and the total energy demand in the system development environments. ............................................................................................................. 83

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Index of Tables Table 1: The total electricity consumption in the Saab facility Järfälla, the measured electricity in

D building and share of electricity consumption per area. ......................................................... 21 Table 2: The measured power demand to the computer labs and the total energy consumption in

computer labs in D building. ........................................................................................................... 42 Table 3: The average power load to one fan coils, the number of fan coils and the total power

requirement. ........................................................................................................................................ 43 Table 4: The measured and estimated average power supply to the cooling units in computer labs.

.............................................................................................................................................................. 43 Table 5: The power load in five different servers during three measurements. ................................ 44 Table 6: The estimated power draw to the servers in D building ....................................................... 44 Table 7: The measured power level in three passive cooling units in D building. ........................... 45 Table 8: The measured power supply to five active cooling units in D building. ............................ 45 Table 9: Measured power draw, pressure development and volume flow rate to the pumps in

cooling system. ................................................................................................................................... 46 Table 10: The result of measured airflow rates in 4 different computer rooms from air handling

units. ..................................................................................................................................................... 47 Table 11: The total airflow rate supplied in the server rooms and computer labs. .......................... 48 Table 12: Supply airflow from the AHUs in the D building. ............................................................... 48 Table 13: The measured volume flow rate of chilled water in the fan coils located in computer

labs in D building. .............................................................................................................................. 50 Table 14: The average volumetric flow rate of supplied chilled water and total refrigeration power

to the cooling units in server rooms. .............................................................................................. 50 Table 15: The average volumetric flow rate of chilled water and the total refrigeration power to

the computer units in the computer labs. ...................................................................................... 51 Table 16: The energy consumption in the defined energy system components in D building. ..... 54 Table 17: The distribution units and corresponding amount of refrigeration power. ..................... 55 Table 18: The power reduction in computers and related cooling system components is illustrated

with related cooling demand by implementing different power settings in the computer labs. The economic model is also presented for estimated PP and LCC. ......................................... 58

Table 19: The location and proposed number of fan coils in the computer labs. ............................ 62 Table 20: The number of fan coils and required effect and volumetric flow rate of chilled water

for 2 proposals. .................................................................................................................................. 62 Table 21: The estimated power draw and annual energy consumption of the fan coils. ................ 63 Table 22: Initial cost of purchasing new fan coils and labor and installation costs for the

suggested proposals. .......................................................................................................................... 63 Table 23: The estimated energy reduction of the suggested proposals. ............................................. 64 Table 24: Summarized life cycle costs, savings and payback time for the proposals. ...................... 64 Table 25: The yearly energy saving for cooling and district heating demand compared to the

current situation. ................................................................................................................................ 65 Table 26: Yearly energy saving in pumps, chiller and cooling units by reduced set point of supply

air temperature in air handling units. .............................................................................................. 65 Table 27: The economic impact of reduced set point of supply air temperature, in air handling

units in D building. ............................................................................................................................ 66 Table 28: The estimated power draw in the AHUs in D building according to the new operation

conditions. ........................................................................................................................................... 67 Table 29: The estimated district heating demand and cost for night cooling through ventilation. 67 Table 30: The investment costs for installation and other required components. ........................... 67 Table 31: The reduction of energy in the ventilation by implementing night cooling through

ventilation. ........................................................................................................................................... 68

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Table 32: The summarized investment, life cycle costs, savings and payback times for the energy measure night cooling. ...................................................................................................................... 68

Table 33: The estimated saving potential from chiller and pumps by replacing the pneumatic thermostats. ........................................................................................................................................ 69

Table 34: The summarized investment costs, savings and payback time by replacing the pneumatic thermostat in the computer lab. ................................................................................... 69

Table 35: The share of investments regarding installation of a new AHU for computer labs. ...... 70 Table 36: The estimated variable cost related to the installation of new air handling unit. ............ 71 Table 37: The potential savings from cooling units and fan coils as well as reduced refrigeration

power and reduced power demand. ................................................................................................ 71 Table 38: The summary of the estimated initial and life cycle costs, saving potential and the

expected payback time. ..................................................................................................................... 71 Table 39: The simulated scenarios with different direction and characteristics of the walls. ......... 73 Table 40: The result of the simulation that states the energy and power demand all three

scenarios. ............................................................................................................................................. 74 Table 41: The estimated saving from reduced energy to pumps, chillers, cooling units and fan

coils by changing the location and orientation of the computer rooms. .................................. 74 Table 42: The economic calculations of the proposal in terms of saving, payback period and

LCC. ..................................................................................................................................................... 75 Table 43: The energy consumption by using hibernate power setting and the savings. Calculations

on LCC are also presented to summarize the total cost of the life cycle of the new proposals. ............................................................................................................................................ 76

Table 44: The power draw and number of bulbs in three server rooms. .......................................... 77 Table 45: The expected costs for occupancy sensors and diverse installation cost. ........................ 78 Table 46: Comparison of the current and the new energy consumption by installing occupancy

sensors in server rooms. ................................................................................................................... 78 Table 47: The estimated investment costs, LCC, saving and payback time by installing occupancy

sensors in server rooms. ................................................................................................................... 78 Table 48: The volume flow and corresponding the supplied refrigeration power in the three main

cooling distribution loops KB01, KB02, KB03 and KB04. The temperature of the inlet and return chilled water in each loop is measured on the outer walls of the distribution pipes. .. 90

Table 49: The volume flow rate of chilled water and required refrigeration power to different cooled areas in the system. ............................................................................................................... 90

Table 50: The momentarily measured power supply to the chiller VKA02. ..................................... 91 Table 51: The measured power supplied to the screens in different power options. ...................... 92 Table 52: Power draw in different model of computers by using different power saving options.

.............................................................................................................................................................. 92 Table 53: Parameters that are used in simulation with "Swegon Esbo". ........................................... 93 Table 54: Cooling demand depending on different orientation and location of the computer labs

simulated with help of “Swegon Esbo Light”. . ........................................................................... 93 Table 55: Impact on the power supply to computers and screen using different power saving

states. ................................................................................................................................................... 94

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1 Introduction The modern society and its basic functions are incredibly depending on different types of energy carriers. A strong energy demand occur especially among developing non-OECD countries, where a strong economic growth, expanding population and improved living standards require increased level of energy use. According to the future energy projections conducted by U.S. Energy Information Administration (EIA), the total amount of energy demand for non–OECD countries are expected to rise by 71 % from 2012 to 2040 (EIA, 2016). Considering the scarce energy sources of the Earth and the need to limit the global warming, several actions and approaches have to be taken to establish enhanced growing societies and to decrease the strong correlation between the energy consumption of growth economy and development (European Union, 2012).

The EU Energy Efficiency Directives, together with the member countries´ action plans to achieve the national goals, sets target to reduce the final energy consumption and concerned with reducing GHG emissions (European Union, 2015). Currently the European Union (EU) climate and energy policies significantly influence the trends in all sector´s energy consumption in OECD Europe through regulatory and market approaches. One of the actions to mitigate the increasing energy use is the so–called 20-20-20 plan that sets three separate target regarding energy by 2020 namely;

• Reduce GHG emissions by 20 % compared to the 1990 level • Increase renewable energy to 20 % of the final energy consumption • Improve energy efficiency by 20 % (EIA, 2016)

Energy efficiency has to be increased at all stages of the energy chain from generation to final consumption and end-users. This is a valuable means to address these challenges and is recognized as one of the lowest cost options to reduce greenhouse gas emissions and thereby to mitigate climate change (European Union, 2012). It is also a one of the most important tools to shape the global energy market and to deliver substantial energy savings (IEA, 2016).

The worldwide contribution of the final energy demand of the building sector has regularly increased to about 40 % of the global energy need (UNEP, n.d.). The energy use of the building sector is accounted for 39 % of Sweden´s total final energy consumption in 2013, where 90 % of the energy in this sector is used in residential and commercial premises. This value is expected to decrease remarkably in the future due to stricter regulation with regard to stricter regulation on indoor climate spaces (Claesson, 2016). Considering the cold climate conditions 60 % of the energy consumption in this sector is used for providing space heating and domestic hot water. During the last two decades the amount of electricity usage in non-residential buildings and commercial premises for service systems and work activities has increased approximately by 40 %, compared to the situation in 1993 (Swedish Energy Agency, 2015). This increased amount of electricity can be the result of an increased use of technological and electrical appliances such as computers, office equipment, monitoring, and telecommunication equipment (EIA, 2017).

Even if the energy use the buildings is expected to increase, this sector holds a large energy saving potential. The necessity of energy efficiency is one of the major steps and needs to play central role in energy policies around the world in order to reduce the energy demand. Yet energy efficiency is far away from being applied in different sectors and fulfills its potential worldwide, where approximately

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two-thirds of the economic potential is last untapped. In addition, 70 % of the entire world´s energy is used without any applications of energy efficiency performance requirements. Reducing the energy demand in buildings by implementing energy efficiency measures has great potential globally (IEA, 2016).

Despite the economic and environmental benefits, the core imperatives of energy policies such as reducing energy expenditures, decarbonisation, air pollution, energy security and energy access, will be attainable for by driving strong energy efficiency policies. In transition to clean energy, efficiency measurement can bring significant multiple benefits such as enhancing the sustainability of energy systems, cheaper energy supply, promoting environmental goals, supporting strategic objectives for economic and social development, and more beneficial across different sectors of the world economy (IEA, 26).

1.1 Background An increased usage of technology and electrical devices during daily activities creates a large amount of energy need in business. Computers, monitors and their applications are one of the basic requirements for delivering services and vital for diverse aspects of operation processes at Saab AB’s facility in Järfälla. The power supply to computers and monitors are, however, responsible for a remarkable part of the total energy usage at the facility and generate considerable energy costs for the company.

Along with the rapid development of technology and innovations, electronic loads have become one of the fastest growing energy demanding end users with varying impact on energy use. This is one of the key drivers of expanded power plant constructions across the world, especially in major developed countries. Computers and laptops and other electronic devices make up a significant share of the energy consumption in buildings and this pattern of consumption is expected to continue growing in the future (Desroches et al. 2014). A study by Urban et al. shows that the total energy consumption of computers is estimated to be 30 terawatt-hours per year in the United States (Urban et al. 2011). The energy consumption of computers and monitors is influenced by two main factors: the power draw and their usage patterns. As the processing power and resolution capacity of monitors increase, these devices tend to use more energy when they are active and lower energy in low power mode (Desroches et al. 2014). An increased awareness on the environmental effects linked to emissions from energy production and the utilization of limited natural resources on the earth, emphasize the importance of not using more energy than necessary during any process.

From a larger perspective the usage of electric appliances, computers and laptops could in fact affect other components of the energy system in the buildings such as the ventilation, the cooling and the heating systems. In addition to electricity consumed to power these appliances, additional energy is required to balance the indoor climate conditions (EIA, 2017). Using electrical devices at a certain place could also have an impact on indoor temperature and humidity, which are all important factors to provide a satisfactory indoor thermal climate. It is therefore important to analyze and evaluate in what extent computers and monitors are used, how much energy they are consuming and what measures can be applied in order to make the energy usage in development environments more effective.

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Even though the current modernizations in working environments are increasingly depending on energy in different forms, it is possible to reduce the energy usage in more efficient ways. One conclusion to be drawn in this concept is that inadequate/incorrect usage of technical equipment, human perception on the limited natural resources as well as potential errors/non-optimization of energy systems generates unnecessary high electricity expenditures.

This study aims to clarify that through implementation of applicable actions on energy usage can considerably be reduced compared to the prevailing situation. This can be done by identification of energy optimization in technical instruments, adjustments in the general energy system and changing some behavioral factors. However, implementation of these measures must take into consideration the most important factors as crucial services and conditions in the working environments.

1.2 Aim and Objective The aim of this master thesis is to analyze the energy system within system development environments in Saab Järfälla. Further investigations are done in order to find possible improvements to reduce the energy demand in D building in the future. Potential methods are developed throughout the working process to investigate how the energy consumption in the working environments is affected by technical aspect, human activities and building criteria’s. The objectives of this work are:

• To analyze and investigate possible errors and impacts of the existing energy system in system developing environments.

• To develop energy efficiency measures at different potential implementation levels in order to reduce the energy consumption related to test environments without affecting the daily activities, services, work environment as well as experienced thermal climate conditions.

The following research questions are evaluated to meet the aim and objectives in this study:

• How the existing energy system works and how does it perform? • How do behavioral and technical aspects within the building affect the electricity

consumption? • How the energy system components cooperate in the system developing environments and

what impact these have on the experienced thermal comfort standards? • What kind of methods/energy measures could be developed in order to reduce the energy

consumption? • What features the potential measures have in terms of technical properties, costs and energy

efficiency? • How could the potential measures be implemented and what are the cons and pros of these

measures?

1.3 Method The aim is achieved partly by a comprehensive literature study in order to find relevant information about the key questions of the concept as well as studying existing scientific reports and previous studies in this subject. This applicable information is used to create a model of measurements and

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work process in order to be able to make further investigation regarding the existing system in the building. In addition, measurements and interviews are contributed as a supplementary perspective on the performance and potential improvements of the energy system at different levels. The most possible energy efficiency measurements will be reviewed from an economical, technical and energy saving point.

The analysis is based on a detailed evaluation and observation of behavioral patterns, frequency of electronic application use, energy demand in a test environment and support system and technical settings of computers/monitors. Examining the energy usage and system functions during nights and weekends with low personal attendance is also of interest.

Considering the built environment, any feasible application on the existing energy system may be relatively complex or impossible. An alternative method in this context is conducting analytical calculations, modeling and observing varying components of interest associated with the existing energy system, in order to investigate the effects of altering factors in the proposed energy measurements. The used methods along with the assumptions, calculation methods and analytical tools are described in detail in order to investigate the prevailing energy situation and finding potential improvements.

1.4 Limitations

This thesis assumes that the working environment consumes more electricity than necessary. Since this study focuses on a theoretical investigation on energy efficiency measures based on real conditions, the result can show differences compared to any real applications of the proposed improvements. In addition, the thermal climate requirements and comfort conditions are estimated according to the Swedish regulations, recommendation and guidelines for building environments. Finally, this thesis will only cover the system and test development environments and related equipment and the energy system components in the D-building at Saab AB in Järfälla.

The main energy subsystem that is crucial for test and system development environment in the investigated building is cooling system and its distribution channels. Therefore this study will primary focus on the cooling demand and the total electricity load that is required for continuous business activities. Since ventilation is one of the complementary systems for cooling supply to the test environments, calculations for cooling demand will take the ventilation system in to consideration.

Generally, the overall system thinking has to be applied to obtain a holistic perspective of the current energy situation. For this reason components to the energy system as well as supporting instruments will be included to the analysis. The system boundaries of test environments include also associated sections such as server rooms, screens and dedicated cooling units in the room spaces.

There are many possible energy efficiency measurements and actions that could be further investigated. However, this study focuses on the most applicable implementations with respect to energy and economic savings.

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2 Company presentation – Saab AB in Järfälla Svenska Aeroplane Aktiebolag (Saab AB) was founded in 1937 with the intent to secure the supply of defense industry during the Second World War and establish a domestic defense industry (Saab, 2017). Today, the primarily focus is the supply of advanced technology products and solutions ranging from military defense, civil security and aviation. In addition, the company concentrates on areas including services, sensors, electronic defense systems and advanced aeronautics as well as submarine systems. The operations are divided in sex different following segments: dynamics, surveillance, support and service, industrial products and services and the business unit Saab Kockums (Saab, 2016).

The company entered the civil aircraft and car market by manufacturing the first aircraft and car in the 1940s. However, the car manufacturing was separated from other activities at Saab Scania when Saab Automobile was sold to General Motors. In 1990 operations of vehicle and aerospace were divided into Scania and Saab and the main activity in Saab comprised aerospace operations. Saab AB has established its position in defense industry by merging the manufacturer of military technology Celcius and acquiring several other key companies and system developers (Saab, 2017). Saab AB has around 14 700 employees and the company has locations in several countries globally, including facilities in different parts of Sweden. The company established first in Linköping where the aircraft 39 Gripen is manufactured (Saab, 2016).

At the facility in Järfälla Saab has its business headquarters, called Security and Defense Solutions specialized in surveillance with over 1500 employees. The building is used for production, system development and technical solution purposes. Figure 1 shows Saab´s facilities in Järfälla.

Figure 1: The Saab facility in Järfäla.

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2.1 Overview of the D building The facility in Järfälla is divided in different larger buildings as it can be seen in Figure 1. D building, referred as D02 in Figure 1, is one of the larger buildings and it has around 450 employees working on five floors with an area of 13465, 2 m2. The building is built in 1990 and consist of a majority of offices, system development environments server rooms and data centers. The main business activity in the building is system development and diverse technical and security solution, which are generally related to computer activities.

2.2 Previous studies Previously two studies were conducted in order to identify the energy consumption patterns and propose different measurers to improve the general energy efficiency in the existing energy system. The scope of the studies covered an electricity survey between different energy consumers and an investigation of the chiller efficiency. Other remaining studies were conducted with main target on efficiency measures in other buildings of the facility in Järfälla.

The first study was an electricity survey that was carried out by Erik Malm in 2012, and aimed to analyze the reason of why the supplied power at the facility did not show any significant variations during a year. This study focused on one specific building and showed that compared to other buildings, the power requirement in D-building during different times of the day was almost at the same level. One of the conclusions that have been carried out in this survey was that the relatively constant cooling related loads caused the largest power draw during nights. Accumulated cooling related loads and power draw to computers consisted of 42 % and 29 % of the total power supply to the building. It was also found that compressors in the chiller plant were the biggest energy consumers in the system (Malm, 2012).

To reduce the energy demand another study performed by Philip Ngo in 2013, which investigated the efficiency of the chillers in D building. An important result found to be that earlier inspections had significant deviations with regard to performance and operation specifications of the chillers. This study showed that the refrigerants did not have the right composition given in the technical specifications. Along with this identification, number of efficiency improvements was suggested to increase the chiller performance in the building (Ngo, 2013).

In 2015, the chillers have been replaced with three new chillers in D building. However, no further studies have been focused on the computer usage patterns or efficiency improvements on the local cooling demand.

2.3 Current energy situation As it mentioned in the previous chapter, a number of improvements are performed in the existing energy system to reduce the energy demand in D building. To be able to compare the energy usage patterns in D building with the facility and analyze if the energy consumption is changed during the last years, an electricity measurement is performed in D building. In this procedure, the current through the three switchgears that supply electricity to the D building is logged hourly during a certain period of time. The measurement took 11 days in March, which was assumed to be qualified as a

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representative consumption pattern throughout a year. The result of this measurement is shown in Figure 2.

Figure 2: The measured power consumption in D building during 2-13 March in 2017.

Based on this result, the average power consumption is estimated to be 456 kW. The total electricity consumption during a year is calculated to be 3997 MWh per year, which is 28,5 % of the total consumption in the Saab facility in Järfälla. The electricity usage in the facility is calculated as a mean value of the available electricity invoices for last three years, that is around 14039 MWh per year. Comparing to the previous studies and statistics, the current electricity consumption at the facility shows a reduction, however the share of the electricity demand in D building is almost unchanged.

The average consumption during a day between 08:00-20:00 on weekdays is around 528 kW, while this value is around 425 kW for non-occupancy hours i.e. during weekends and nights. These values show a difference compared to the study done by Erik Malm. Compared to Malm´s results in 2012, the daily consumption is reduced by 13 % while the consumption during unoccupied hours is decreased by 12 % (Malm, 2012). However, the main concern in Malm´s study remains, where the electricity demand during occupied and unoccupied hours does not show any significant difference.

The total electricity demand in the Saab facility Järfälla and the measured electricity in D building along with the electricity consumption share per area are presented in Table 1. Additionally, the electricity consumption share per area in D building is higher compared to the electricity need in the whole facility.

250

300

350

400

450

500

550

600

1703

02

1703

02

1703

03

1703

03

1703

03

1703

03

1703

04

1703

04

1703

04

1703

05

1703

05

1703

05

1703

06

1703

06

1703

06

1703

06

1703

07

1703

07

1703

07

1703

08

1703

08

1703

08

1703

08

1703

09

1703

09

1703

09

1703

10

1703

10

1703

10

1703

10

1703

11

1703

11

1703

11

1703

12

1703

12

1703

12

1703

13

1703

13

Pow

er [

kW]

Hours [h]

Power consumed in D-building

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Table 1: The total electricity consumption in the Saab facility Järfälla, the measured electricity in D building and share of electricity consumption per area.

Electricity consumption

[MWh/year]

Share of the total electricity usage

[%]

Total Area

[m2]

Electricity consumption share per area [kWh/m2]

D building 3997 28,5 13465 296,8

Saab facility in Järfälla

14039 100 76000 184,7

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3. Literature review This chapter presents an informative and technical theory about cooling systems, configurations, components and working principles in detail. This part aims to give a ground for a comprehensive knowledge about the energy systems in buildings in general.

3.1 HVAC systems Heating, Ventilation and Air conditioning (HVAC) systems are crucial tools to maintain satisfying indoor climate conditions for the occupants in buildings. These systems have the primary function to provide the required cooling, heating and air-conditioning indoors. Although the system configuration, arrangement and construction may differ, they generally contain similar components such as fans, pumps, ducts, pipes, dampers, valves and cooling/heating exchangers (Claesson, 2016).

HVAC systems should have a control and regulation system in order to establish thermal comfort and energy efficiency in accordance with the Boverkets regulations in Sweden. These systems should be fitted in automatic regulation appliances that will ensure supply of heating and cooling is adjusted in relation to the outdoor and indoor climate. In addition, location, the climate impacts and building characteristics has to be considered in design of HVAC systems (Boverket, 2011).

Classification of the systems depends on the energy-carrying medium. The most common types of HVAC system are:

• Air-air systems • Air and water systems • All water systems (Claesson, 2016)

3.1.1 All-air-systems In these systems, the cooling and heating are added into the ventilation air, which is supplied into the building through ventilation ducts. All air system does apply any hydronic loops, where liquids are the heat transfer medium (Claesson, 2016).

Air to air systems are used for supplying sensible and latent cooling, preheating and humidification to the ventilation air. It is possible to accomplish heating by the same airflow in the central system or in a separate segment or by using independent heaters. This type of system is usually applied in building that require individual control of multiples areas such as office buildings, hospitals, schools and universities (Claesson, 2016).

The central mechanical room of these systems is usually located outside of the occupied spaces. These properties gives advantages including maintenance and operation in unoccupied zones, keeping the vibration and noise-producing equipment outside and away from conditioned spaces, implementing heat exchanger for effective heat recovery. Furthermore, the location gives possibility to benefit from free cooling (outside air) instead of mechanical refrigeration for cooling. However, the major equipment of the system requires additional duct clearances, which result in reduced usable floor space and increased building height. All air systems can be divided into many different configurations e.g. single zone systems, dual –duct systems and variable/constant volume systems (Havtun et al. 2011).

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3.1.1.1 Single zone systems

In single-duct systems represent the simplest system design e.g. Air Handling Unit (AHU) that is intended to serve single zones. In case of required ventilation in larger buildings that contains several zones, several AHU is required. In single zone systems, the air is distributed in a common distribution system that transfers ventilation air to the different parts of building with same air temperature and state. A drawback of the system is that all zones in a building receive air conditioned at the same state, unless locally installed heat and cooling devices in separate zones are included. To meet the required conditions in the air conditioned areas, cooling and heating coils are placed in series in the airflow passage to achieve the set point of desired temperature and humidity (Claesson, 2016).

3.1.1.2 Variable –volume systems (VAV) & Constant-volume systems (CAV)

Another configuration of air-air systems is Variable Air Volume system (VAV), where the supplied air in to the occupied zone is conditioned according to predefined conditions centrally in AHU. The distribution of airflow to different zones is arranged to vary depending on the demand. A variable speed control fan regulates the amount of flow rate into each of the individual zones in a building. An important mechanism in these systems is having a control signal that sends static pressure to adjust the airflow rate in the variable speed control fan. The speed control can contribute to reduce the operation cost of fans by decreasing the fan speed depending on the varying demand in the zones. Since the VAV systems are almost self-balancing, the design of ducts in not a crucial factor.

The control adjustments in VAV systems can include local heaters and coolers in order to improve the control between temperature level and air pollutants (e.g. humidity and CO2). By this, the ventilation air can focus on meeting a sufficient level of the air pollutants indoor, while heaters and coolers located in each zone provide the thermal loads based on the demand. An example of this configuration is shown in Figure 3. These types of VAV systems are rather air-water system than all air systems. Hence, they include hydronic loops and are aimed to meet varying loads in each individual zone.

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Figure 3: Configuration of VAV air water systems (Claesson, 2016).

Unlike VAV system, Constant volume systems (CAV) provide constant level of airflow. The limitation of this configuration is that the varying demand of airflow is not taken into consideration, which can be crucial for operation costs and achieving adequate thermal conditions (Claesson, 2016).

3.1.1.3 Dual-duct systems

Another example of all air systems is dual duct systems that are constructed with parallel heating and cooling coils to distribute the air in buildings. Dual duct system is the most adaptable ventilation system to meet various demands in different zones within a building. The airflow is distributed to each zone either by blending the air at the terminal device or supplied to each zone by a separate distribution system, where air is mixed to reach the desired state (Claesson, 2016).

3.1.2 Air- and water systems In a typical construction of air-water system the properties of air and water are used in order to supply the required energy into the habitable spaces in buildings. The air and water are heated/cooled in centralized systems, and then are distributed to terminal units installed in spaces.

In general, the supplied air is called primary air and water is called secondary water. Air- and water systems consist of different compounds including central air-conditioning equipment, water distribution systems, ducts and room terminals. Room terminals refer to units that can dissipate heating/cooling by i.e. convection or radiation principles. Examples of typical room terminals are fan coils or conventional supply air outlet combined with a radiant panel. The central air conditioning equipment supplies the necessary ventilation in different points of a building. Secondary water distribution combines water distribution systems, where chilled water is circulated through hydronic loops to room terminals or cooling/heating coils in AHU (Claesson, 2016;Havtun et al. 2011).

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3.1.3 All-water systems In the all water systems, the centrally produced water is circulated through hydronic loops. Duct is not a part of all water system, where pipes and hdronic loops transfer all fluid/water. All-water systems use hot/cold water that circulates in the room terminals for space conditioning. Heat is transmitted in to the room by conduction, convection, or radiation between the air in the space and the hot water. The distribution system needs less building space, a small duct space and a smaller/no central fan room compared to all air systems. The construction of this of systems allows the application of a central water heating/cooling plant, while retaining the capability to control the flow rate in each individual space. However, all-water systems require more maintenance compared to central all-air system with an additional drawback of maintenance that may take place in occupied zones.

There are numbers of different types of all-water systems including; baseboard radiation, wall, floor, or ceiling panels, fan coils, bare pipe (rocked on the wall) and free standing radiators and convectors. In addition, the systems can be further classified in several ways such as convection heating systems and radiation systems, natural or forced circulation, one-pipe or two-pipe systems. The most common application that used in heating systems are two-pipe systems, which have one supply and one return line of hot water. The main benefit here is that all radiators receive the same water with almost the same temperature level (Havtun et al. 2011).

3.2 Cooling systems Cooling systems are designed to maintain the thermal comfort standards and remove the heat from occupied zones and maintain it at a temperature lower than outdoor temperature. The temperature of body or fluid is reduced when the internal energy is removed from the substances and maintains the temperature of the body below the temperature of surroundings. To accomplish this, heat should be dissipated from a lower temperature source to higher temperature level. The second law of thermodynamics states that, heat transfer is possible only from the higher temperature to lower temperature. This means that such a heat transfer is possible only if work/energy is added to the system. This is achievable by applying a cycle operation between the desired lower temperature and the higher ambient temperature (Jayamaha, 2006).

COP2 value is a crucial and widely used parameter that indicates the performance of a refrigeration cycle with respect to the work added and useful refrigeration power produced. The ratio between useful refrigeration power and necessary energy requirement is called coefficient of the performance in a refrigeration cycle:

𝐶𝑂𝑃! =!!!

(1)

In Equation 1, (COP2 ) is coefficient of the performance, (Q2) is the useful refrigeration power and (E) is the necessary operating energy in this relation (Granryd et al. 2011).

3.2.1 Vapour compression cycle Vapor compression cycle is the most commonly used refrigeration method that is applied on air conditioning, heat pumps and central chiller systems. The main aim in this cycle is to reject heat to surroundings from higher temperature source and extract heat at low temperature sink. According to the first law of thermodynamics the heat rejected from a body is equal to the sum of heat absorbed at a low temperature level and the net energy input required to operate the cycle. The consumed

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mechanical energy is used to lift the refrigeration circulation from low to the higher temperature. Most of the application of refrigeration, cycle operated with mechanical work is predominant.

The fluid used in the reversible refrigeration cycles called refrigerants. Refrigerants evaporate at lower temperatures and condense at high temperatures. Basically, refrigerant has the capacity to evaporate at low temperature and pressures by absorbing heat, and then condense at higher temperature while releasing the heat that is extracted.

The vapor compression cycle has four main components through which the refrigerant is distributed in a closed loop and these components are expansion valve, evaporator, compressor and condenser. The refrigerant enters the compressor at low pressure and temperature level and is compressed to high-pressure vapor. The high-pressure vapor enters the condenser in order to realize the heat added. A heat exchanger/heat sink captures a certain amount of heat in the refrigeration, which leads to a change phase in refrigerant from high-pressure vapor to high-pressure liquid. Afterwards, the high-pressure liquid continues to circulate through the expansion valve and expand further to low-pressure liquid and send to the evaporator. This cycle is flowed by heat absorption between the refrigerant and heat source/brine water. Generally, the refrigerant in evaporator has to be at a lower temperature level compared to the heat source to be able to gain heat and vaporized at low pressure. Than the low-pressure vapor refrigerant finally enters the compressor and this cycle continues to repeat itself in this order. Figure 4 shows a basic compression cycle with the components and the flow direction of refrigerant (Jayamaha, 2006).

Figure 4: Vapour compression cycle and the main components (Bright hub engineering, 2016).

3.2.2 Components and configurations

In this section the main components of a vapor compression cycle will be presented for the technical properties, working principles and different application areas.

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3.2.2.1 Compressors

Compressors are one of the four main hardware components of refrigeration systems. The purpose of using compressors in vapor compression cycles is to transfer the refrigerant vapor from low pressure in the evaporator to the high pressure in the condenser. Compressors and their efficiency have a strongly influence on the system performance in refrigeration, air conditioning and heat pumping systems.

The main types of compressors used today are reciprocating, screw, centrifugal and scroll. Different compressor designs have different suitable application and usage pattern. These types of compressors are “displacement compressors”. All the compressors work according to the principle that the vapor is captured in a space, which is eventually reduced during the axis rotation in a compressor. As a result to the volume reduction, the pressure and temperature of the gas increase and will be delivered to the high-pressure side or condenser inlet.

Reciprocating compressors include a piston and a connection rod that is driven by a crankshaft, which in turn is driven by a motor. In hermetic systems, the compressor and the motor is maintained inside a common housing, where the motor and crankshaft are in direct contact with the refrigerant gas. Compared to an open type system, where the motor is mounted externally and is connected through a crankshaft that extends through a seal out of the crankcase. Usually these compressors may have a number of cylinders in one unit. The inlet gas is sucked into the cylinder and expands as the piston moves downwards inside the cylinder the volume increase. As the piston moves up and reaches its top position inside the cylinder the gas will be compressed to high-pressure level and discharged.

Screw compressors are usually used for medium-capacity application that gives about 50 kW to 1,7 W operating power. They consist of twin compressors with two rotors that matches screw profiles, namely one screw and one slide motor. These, which are the only moving parts in the compressor rotate inside an enclosed housing and reduce the volume of the inlet gas. Gas passing through the inlet port fills the volume between two rotors. Due to the rotation of the rotors the inlet gas will be compressed as the volume decrease. As the rotation continues the gas is subsequently delivered to the discharge port.

Centrifugal compressors are used for high capacity applications and reaches the capacity of an inlet flow rate of about 2000 m3 /h and upwards. It includes different number of impellers mounted on a shaft and rotating inside an enclosure. The refrigerant vapor enters the impellers at axial direction and leaves it radially at high velocity. The velocity pressure is then transformed to static pressure in the diffuser.

Scroll compressors are formed to use two “orbiting scroll”. The spiral shaped scrolls is mounted in the same orbit. One of the scrolls has a fixed position while the orbiting scroll rotates. Due to the shape of the scroll the gas enters the opening between the volume of scrolls and it is compressed between the fixed and orbiting spirals. Normally, scroll compressors are used for low-capacity applications (Jayamaha, 2006; Granryd et al. 2011),

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3.2.2.2 Condenser

The main function of a condenser is to transfer heat from the refrigerant to the environment or heat sink. As it mentioned before, the refrigerant leaves the compressor as a superheated vapor and enters the condenser. When the refrigerant is discharged from condenser it change phase to slightly sub-cooled liquid. This principle is used to deliver heat to indoor environment in heat pump or to the hydraulic heating systems. The overall efficiency of a refrigeration cycle or heat pump depends strongly on the effectiveness of the heat transfer between the refrigerant and the heat sink. Theoretically, the amount of rejected heat increases at a lower evaporation temperature of refrigerant (Granryd et al. 2011).

Condensers can be divided into three different types depending on the heat sink or cooling medium used in the refrigerant cycle. These are: air-cooled condenser, water-cooled condenser, and evaporative condenser. Air-cooled condensers can be applied in both large industrial applications but are more dominant in small systems such as domestic refrigerators. This is due to the low heat exchange potential between air and refrigerant. Air-cooled condensers for forced convection, also called fan coils, are designed with fin-on-tube arrangements in small units of refrigerant power (Granryd et al. 2011).

However, water is a significant coolant that includes several advantages in design, and low initial cost due to its high heat transfer characteristics. In evaporative condensers, circulating a condensing coil, which is continuously wetted on the outside by water, cools down the hot gas from the compressor. These types of condenser need less water pumping and chemical treatment than water-cooled condensers (Granryd et al. 2011).

3.2.2.3 Expansion valve

In a compressor driven refrigerant process, expansion valves are used to maintain the pressure difference between the high-pressure (condenser) and low-pressure side (evaporator). In addition, using expansion valves have the purpose to regulate the flow of refrigerant in order to match the heat transfer in the heat exchangers. There are a number of different expansion valves applied to meet different demand and capacities in refrigerant systems. The most common expansion valve is the thermostatic expansion valve that regulates the refrigerant flow to maintain the same superheat at the inlet in all conditions. The rate of flow through a valve depends on the pressure difference across valve orifice and the valve opening is regulated according to the demand of the evaporator (Granryd et al. 2011).

3.2.2.4 Evaporator

In an evaporator the slightly sub-cooled refrigerant flow enters the evaporator in a liquid state. Inside the evaporator the liquid gains heat and evaporates by heat transfer between the refrigerant and the heat source. After the heat transfer the liquid is discharged from the evaporator. During this process, the temperature level of the refrigerant remains constant, as the pressure is constant. The temperature of the refrigerant must be lower the heat source to ensure a heat exchange. In conventional refrigeration operations the heat source represents the heat transferred from food inside freezer (Granryd et al. 2011).

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3.2.2.5 Refrigerants

Refrigerant is a substances or a mixture that is used in vapor compression cycles as a working fluid. In conventional refrigeration cycles, the working fluid goes through a phase transitions i.e. from a gas to liquid and then to gas again. This cycle is repeated as compressors are in operations.

There are two main requirements that a working fluid in vapor compression cycle has to fulfill. The first one emphasizes the importance of not causing any risks of fire or damages in case of a leakage. The second qualification refers to compatibility of refrigerant that suit the working conditions in the system to the lowest possible cost. To suit these factors, the chemical and physical and thermo dynamical properties of a working fluid have to be carefully considered. Due to these requirements on the selection of refrigerants, it is often difficult to find an ideal refrigerant. However, in this case refrigerants should be selected with respect to the specific application. Selection of a working fluid should be based on chemical stability within the refrigeration cycle. This is one of the most crucial criterions to avoid risk of working fluids that decompose or react with diverse materials in the system.

The thermodynamic and transport properties of a refrigerant have significant impact on the performance of the refrigeration cycle. Another desired criterion is the pressure level that should not be too high or too low. If the pressure drops under the atmospheric pressure, air can be sucked into the refrigeration system and thereby cause ice plugs in the expansion device and inert gases in the condenser.

During the last century chlorofluorocarbons (CFCs) and hydro chlorofluorocarbons (HCFCs) were widely used in diverse applications. Since evidences from several studies showed that these refrigerants deplete the ozone layer, huge efforts were made to phase out and replace CFCs and HCFCs. Some of most commonly used refrigerants today are ammonia, propane and hydro fluorocarbons (HFCs) (Granryd et al. 2011).

3.3 Cooling distribution systems There are numerous air-conditioning systems used in buildings, such as variable refrigerant volume systems, stand-alone package units, central systems and water-cooled package units. Central air-conditioning systems are the most commonly used air refrigeration system in large buildings and commercial buildings, where the cooling demand is high.

In a typical central air-conditioning system, the evaporator of a chiller cools the heat source/chilled water. Chilled water is distributed by a pump, to AHU units, fan coils, and heat exchanges positioned in different parts of a building. To dissipate the cooling, there are fans installed in fan coils, chilled baffles to blow the air through heat exchanger coils and transfer the heat from the air to chilled water. After the heat exchange, the heated chilled water is transferred back to the evaporator of the chiller to be cooled down and to preserve the continuous cycle.

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3.3.1 Fan coils units A fan coil unit (FCU) is a mechanical device to deliver cooling and/or heating, which consists of a heat exchanger or (heating or cooling) coil and a fan. The application of fan coil units has a primarily purpose to control temperature in the space where it is installed. Central heating and cooling plants supply the required heating and cooling to the heat exchangers in the fan coils. Regulation of this type of systems is based on manually controlled thermostat, which regulate the amount of water through the heat exchanger by using a control valve and adjustable fan speed (Kahazaii, 2014). Fan coils have the advantage to be easily applied and control individual zone temperatures, especially in spaces where prevention of cross-contamination between rooms is necessary (InventiAir, 2017). Energy is consumed due to the supply of electricity to the fan motor that circulate the generated heated /cooled air inside the zone (Kahazaii, 2014).

Various unit configurations of fan coils are available, such as horizontal or vertical fan coils. However fan coil units can be categorized into two main types: Two-pipe fan coils and four-pipe fan coils. In two-pipe coils there are one supply and one return pipe to condition the space, while in four-pipe systems have two supply and two return pipes. The configuration of four pipe fan coils allows supply of hot or cold water into the fan coil units at any given time. Fan coils can also be named after the placement. A fan coils can be installed along the inside of the wall or ceiling. A fan coil unit connected to the wall under the window draws the under pressurized air in order to send it through the heat exchanger/battery to generate the air to the desired state. The heated or cooled air blows out of the fain coil with a vertical airflow, which create a high pressure in the room air (InventiAir, 2017). An illustrative picture of a fan coil unit is shown in Figure 5.

Figure 5: Basic configuration of a vertical fan coil (Claesson, 2016a).

3.3.2 Chilled baffles Chilled baffles are component in HVAC systems designed to meet the demand for local cooling. Chilled baffles transfer the heat by forced convection principle using a fan and are usually installed on the ceiling. The chilled water from the chillers circulates through a heat exchanger coil and cools down the air, which afterwards blows down from the unit. As the heat exchanger coil cools down the air, the

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air becomes dense and sinks to the floor. The warm air that is replaced by the cooled air moves up due to the pressure differences. The heated air flow towards the fan through a filter, which cause a continuous air motion of the indoor air. Chilled beam can be integrated with supply air connections in order to serve as air supply tools and in many cases increase the cooling capacity in baffles. Capacity of the cooling effect is regulated with control valve that adjust flow rate of chilled water in order to meet the desired cooling level. The working principle of chilled baffles are quite similar to fan coils, which also contains similar components.

3.3.3 Computer room air conditioner (CRAC) Server rocks constantly dissipate heat that needs to be removed in order to maintain the range of recommended conditions by the manufacturer. Removing the heat from server halls aims to prevent the operations from the risk of overheating that can result in malfunction, damages of the hardware and interruption of business processes. This type of risk costs high and need to be eliminated in advance. Therefore it is important to cool server rooms to sufficient level of temperature and humidity without using excessive forced cooling that lead to economic losses and waste of energy. These types of passive or active cooling units supply cooled air in the room by heat transfer from the chilled water that cools down in the evaporator and transferred through sealed chilled water loops. Placement of the cooling units is usually fixed but server rocks can be moved.

Recommended range of maximum allowable air temperature and humidity in front of server racks are specified by ASHRAE´s thermal guidelines. According to the guidelines the recommended temperature and humidity range is 18-27 °C and 60 % RH. The allowable temperature and humidity range defined to be 15-32 °C and 20-80 % RH (ASHRAE, 2011).

The first law of thermodynamic states that in steady state operations the energy input into a system is equal to the energy output from the defined system. Considering that, the only form of energy that leave the electrical instruments is heat that is generated as the current goes through resistive elements. Here, it can be concluded that the power consumption of an electrical device is equal to the heat dissipation. In 2010, the electricity usage in data centers was estimated to around 1.3 % of the total electricity consumption in the world (Koomey, 2011).

Computer room air conditioning units are located in the room space and cools down the hot return air generated by the servers. These cooling units cool the hot air as the air circulates through a heat exchanger. Chilled water in the heat exchanger can be supplied either by inbuilt refrigeration unit or a chilled water loop connected to a chiller plant. A typical configuration for delivering the cold air in the server rooms is using raised floor, which is shown in Figure 6. Cold air in the raised floor usually provided to the room space from the subfloor pressurized plenum using perforated floor tiles (Arghode et al. 2016).

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Figure 6: Typical "raised floor" cooled server room (Jonsson, 2009)

3.4 Control systems 3.4.1 Pumps

A pump is a mechanically or electrically driven component that usually brings the driving forces to create a forced circulation of fluids. The most common systems are used for pumping hot water in central heating systems or pumping chilled and condensed water in air conditioning system in a closed loops. The main purpose of pumps is to overcome the flow resistance in hydraulic systems and give primarily force to distribute the necessary heat or cold water to different point of a building. In hydraulic systems the centrifugal pumps are the most common type of pumps that are used (Granryd et al, 2011). Since centrifugal pumps and fans have very similar operation properties, the theoretical characteristics of can be applied on fans. In this pumps the fluid pass into the pump axial to the centre, and the fluid direction is deflected 90 ℃ just before the entrances to impellers. Inside the impellers the fluid flow a radial direction, where rotation increase the angular momentum of the fluid. As the fluid discharged from the pump the imposed angular momentum is into static pressure with increased area, hence reducing the velocity of the fluid (Jayamaha, 2006).

Pumps are used to offset the pressure losses in the system such as, frictional losses, pressure losses across the valves, cooling coils and static head differences in open systems. Pressure head and flow rate are two of the most important parameters when selecting the right size of pump. Pumps (and fans) gains a certain pressure level at a certain rotational speed and flow rate. Increasing the speed of propellers yields a higher-pressure difference as well as increased flow rate of the fluid. The relationship between flow rate of fluid and pressure development is called pump curve.

A pump that will serve a system has to be carefully selected to match the performance. The size and design of a pump based on set point conditions, which vary with time, load and design operation point. However, a crucial criterion of pumps is to be sized to satisfy the peak load conditions. The design flow is arranged to overcome the resistance and losses in the systems. Losses due to the friction and valves are normally estimated using specifications and research data provided by manufacturers (Granryd et al, 2011).

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4 Methodology This chapter present the methodology that is used in this project to organize system thinking, clarify the system boundaries, and create base for improvements of the existing energy system.

4.1 Methodology overview An overall energy survey offers possibilities to evaluate the existing energy system at different levels, analyze energy subsystems and compounds. In this regard, the method is divided into three stages for narrowing the research area of interest and investigates the potential energy efficiency proposals. This also enables to inspect and track all deviations and improvement possibilities in the existing energy system. The following steps are carried out in order to implement this approach in the study:

• Initially, an energy survey is conducted to be able to identify the energy demand within system development environments and related equipment. For this step, the energy systems and associated compounds in the system development environments are identified. This is an essential step to establish the energy system boundaries, structure and connections.

• This is followed by a detailed investigation of the system performance, configuration and interaction that can indicate the current energy usage. Measurements on different levels of cooling, ventilation system and electricity demand is evaluated.

• Possible improvements are suggested to increase the energy efficiency and reduce the yearly running costs of energy in the building. The suggested energy efficiency measures are analyzed with respect to the potential energy and economic savings as well as payback period for the investments.

•

4.2 Existing energy system To initiate this study, a number of energy surveys and observation is conducted to analyze the general energy system in D building. This is a brief survey, aiming to gather the necessary data collection of the existing energy system and its components as well as to investigate the energy flow in the system. A holistic perspective on the energy flow in the current energy system, connections and components are shown in Figure 7.

All incoming energy forms to the facility is provided in terms of electricity and district heating, which are supplied by two companies, namely Vattenfall and E.ON. Heating is primarily used to provide comfort heating through the fan coils installed in each office space. District heating is also used for hot tap water supply through heat exchangers in different stages of the energy system. To meet the hot water need during summers, a heat pump operates constantly in order to reduce the supply of district heating.

Electricity is the main energy form that is used to operate diverse electronics, computers, servers, fans coils, AHU and cooling units. Electricity is also used in various components to provide cooling for different applications. All the cooling in D building is supplied from the chiller, which in turn need electricity to operate the compressors and proceed the refrigeration cycle. Pumps transfer the chilled

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water through sealed loops to various cooling components such as cooling units, fan coils, cooling coils in AHU etc.

Figure 7: A schematic overview of the existing energy system configuration and related subsystems in D building.

4.3 Energy system boundaries The system boundaries around system development environments include equipment and energy sub-systems that are important for continuous business operations. Considering all the existing components and sub-systems included in the defined system boundaries, this study covers the supply of cooling and electricity of the following components of the energy system:

• Computer labs • Fan coils • Cooling units in computer labs • Servers • Cooling units in server room • Pump • Ventilation • Chillers

The process to analyze the energy requirements of the defined system is divided in two parts. The first part consists of an investigation of the power demand in the defined energy system components. This is a general electricity survey that aims to estimate the yearly electricity consumption to each of the individual components. In the second part, the cooling demand required to each of the components is estimated. Since, all the cooling needed in the computer labs and server rooms originate from the chillers, the cooling demand has to be determined in order to estimate the required power input in the compressors of the chillers. Furthermore, identifying the cooling demand and volume flow rate of the

Energy

Electricity

Computer / Server room / Lighting/ Electronics Chillers & Pumps

Cooling units

Fan coils

Chilled baffles

AHU

AHU

District Heating

Fan coils

Domestic hot water

AHU

-35-

chilled water in these environments makes it possible to find the required energy for the pumps in order to deliver the necessary cooling.

-36-

5 Calculation methods The calculation method used in the context of this study is described in the following section. The given equations and relations are applied to estimate volume flow rate of cooling water in pumps, the cooling effect transferred to the system and energy consumption in diverse applications as chillers, pumps, fans, servers, cooling units, air handling units and computer labs.

5.1 Refrigeration capacity The cooling effect or refrigeration capacity (𝑄) basically refers to a cooling system´s capability to remove heat. It describes the cooling that can be delivered by means of fluid with a specific volume flow and a temperature exchange between the entering and existing cooling object, which is given by the flowing relation:

𝑄 = 𝑉 ∗ 𝜌 ∗ 𝐶𝑝 ∗ ∆𝑇 [W] (2) 𝑄= Refrigeration power [W]

𝑉 = Volume flow rate [!!

!]

𝜌 = Density of fluid [!"!!]

𝐶𝑝 = Specific heat capacity [ !!"∗!

]

∆𝑇 = Temperature difference between incoming and returning fluid [K], (Granryd et al, 2011).

For the estimation of the transferred refrigerant effect in the cooled water and brine water in the chiller and cooling system, the following assumptions are made:

For water at atmospheric pressure (at 20 °C):

𝐶𝑝 = 4200 J/kg*K 𝜌 = 1000 kg/m3

5.2 Pumps and volume flow rate For incompressible fluids such as cooling water, where density is almost constant at the inlet and outlet of the pipe that has the same cross section area can be rearranged by the given relation:

𝐸 = ! (!!!!!)!

[W] (3)

Equation (3) gives the theoretical work required in a pump to transport the fluid. To estimate the mechanical power requirement for a motor that actives a pump can be estimated by taking the efficiency of pump into consideration:

𝐸! = ! × ∆!!!

[W] (4)

𝐸 = Theoretical power required for pump

𝐸! = Power required for pump [W]

𝑉 = Volumetric flow [m3/s]

∆𝑝 = Pump pressure difference [Pa]

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𝜂! = Pump efficiency

𝑝! = Pressure at the inlet of the pump [Pa]

𝑝! = Pressure at the outlet of the pump [Pa]

𝑚 = Mass flow of the fluid [kg/s]

𝜌 = Density of the fluid, kg/m3, (Granryd et al, 2011).

The available pump curves to some pumps were used for identification of the required mechanical power. When pump curves and other necessary information were not accessible, Equation 4 used to calculate the mechanical power along with the assumption of 65 % pump efficiency.

5.3 Affinity laws The performance of a pump or a fan under different conditions follows the affinity laws. Affinity laws consider the pressure development across a pump/fan, rotational speed, and flow rate and power demand to the motor. Affinity laws are useful tools to estimate/adjust the system performance to the pump performance (Jayamaha, 2006).

𝑄! = 𝑄! ∗ !!!!

(5)

∆𝑝! = ∆𝑝! ∗ !!!!

! (6)

𝐸!! = 𝐸!! ∗ !!!!

! (7)

Q = Change in speed [l/s]

N = Change in speed [rpm]

∆𝑝 = Change in pressure [Pa]

𝐸! = Change in power demand [W]

5.4 Power draw Evaluation of the power draw to various electronic applications is based on measuring the current in different phases. The net power to operate the appliances is given by:

𝑃 = 𝐼! + 𝐼! + 𝐼! ∗ 𝑉 ∗ cos𝜑 (8)

P = Power [W]

𝐼 = Current [A]

V = Voltage [V]

cos𝜑 = Power factor

For appliances that include a motor to run such as pumps or compressors, the power factor was assumed as 0, 8. In other cases, when electricity is directly enters the appliances as in a computer or a server the power factor is assumed as 0, 9.

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5.5 Cooling and heating in the AHUs For estimating the efficiency of the rotary heat recovery units in the air handing units the following equation is used:

𝜂!"# = !!!!!!!!!!

(9)

𝜂!"# = Efficiency of the rotary heat exchanger

𝑇! = Ambient air [°C]

𝑇! = Supply air [°C]

𝑇! = Exhaust air [°C]

The supply air in to the building is the predefined set point at 19°C for all the existing AHUs. Estimation of the exhaust air temperature leaving the occupied areas is based on several measurement of the offices and computer labs, which resulted in an average air temperature of 22 °C and used in the Equation 9. Since the ambient air temperature alters depending the prevailing climate conditions, the ambient air temperature is estimated as the average hourly temperature in Stockholm in 2009-2016 (SMHI, 2017).

Climate dependent cooling and heating emerge when the outside temperature is lower or greater than the pre-set supply air temperature, which 19°C. Due to the lack of measurement instrument, only sensible heat was included in the calculations of the cooling needed in the ventilation system. Based on these assumptions, the following relation can calculate heating and cooling effect that required for the supply air in the ventilation system:

Cooling: 𝑄 = 𝑉 ∗ 𝜌 ∗ 𝐶𝑝 ∗ (𝑇! − 𝑇!) [W] (10)

Heating: 𝑄 = 𝑉 ∗ 𝜌 ∗ 𝐶𝑝 ∗ (𝑇! − 𝑇!) [W] (11)

𝑄= Refrigeration or heating effect [W]

𝑉 = Volume flow rate [!!

!]

𝜌 = Density of fluid () [!"!!]

𝐶𝑝 = Specific heat capacity [ !!"∗!

]

∆𝑇 = Dry bulb temperature difference between incoming and outgoing fluid [K]

𝑇! = Ambient air [°C]

𝑇! = Supply air [°C], (Granryd et al. 2011).

For estimation of the transferred refrigerant effect in the cooled air in the central AHUs following assumptions are made:

𝐶𝑝 = 1000 J/kg*K 𝜌 = 1,2 kg/m3

-39-

5.6 The economic model The evaluation on the profitability and economical outcomes of the proposed energy efficiency measures is conducted by using two different economical models.

5.6.1 Payback period

Pay back period (PP) is used for economic calculation of the suggested energy efficiency measures in this study. This method is used as a base for evaluation of time frame that is required to compensate the initial investment in each proposed project or energy efficiency measure.

𝑃𝑃 = !!!!

[Year] (12)

In Equation 12, (PP) gives the payback period, (T) is the initial investment, (a) is the sum of the annual incomes and (k) stands for annual running cost. The price of electricity assumed to be 1 SEK per kWh.

5.6.2 Life cycle cost (LCC)

Life cycle cost refers to the costs that emerge from an ownership of an asset´s entire lifespan. This method considers expenditure including planning, design, acquisition, operation maintenance, depreciation, replacement and disposal. LCC is developed to assist the decision-making in comparison of the actual cost of different assets (Dahlberg and Norrbrand 2003). The assets total life cycle costs are calculated according to the following equations:

𝐿𝐶𝐶!"!#$ = 𝐶!"#$%&'$"& + 𝐶!"#$%&$"$'& + 𝐶!"!#$% − 𝐶!"#$% !"#$ !"#$% [SEK] (13)

Net present value of maintenance costs (𝑪𝒎𝒂𝒊𝒏𝒕𝒆𝒏𝒂𝒏𝒄𝒆)

𝐶!"#$%&$"$'& = 𝑎!"#$%&$"$'& ∗ !!(!!!)!!

! [SEK] (14)

Net present value of energy costs (𝑪𝒆𝒏𝒆𝒓𝒈𝒚)

𝐶!"!#$% = 𝐸!"!#$% ∗ 𝑒!"!#$% ∗ !!(!!!!!!)

!

!!!!!!!!

[SEK] (15)

Net present value equipment value final year (𝑪𝒓𝒆𝒔𝒊𝒅𝒖𝒂𝒍 𝒗𝒂𝒍𝒖𝒆)

𝐶!"#$%&'( !"#$% = 𝑐!"#$%&'( !"#$% ∗ (1 + 𝑖)!! [SEK] (16)

-40-

𝐶!"#$%&'$"& = The initial investments [SEK]

𝑎!"#$%&$"$'& = Annual maintenance costs [SEK/year]

𝐸!"!#$% = Annual energy requirement [kWh/year]

𝑒!"!#$% = Current energy price [SEK/kWh]

𝑐!"#$%&'( !"#$% = Equipment value final year [SEK]

𝑛 = Years of operation [year]

𝑖 = Rate of discount [%]

𝑞 = Annual increase in energy price [%], (BELOK, 2017)

Estimations on the economic analysis are based on assumptions of 10 years of operation and 5 % of discount rate as well as 1 % of annual increase in energy price.

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6 Energy mapping This chapter aims to explain the procedure of the conducted measurements in the energy system components that are associated with the system development environments. In general, these measurements aim to investigate the total energy consumption in terms of electricity and cooling demand in the defined system boundaries.

6.1 Electricity survey 6.1.1 Computer labs The system development environments also referred as computer labs or computer rooms are among the most crucial spaces to develop the test computational and simulation based operations at the company. These environments are open plan offices, which consist of high number of computers and screens and have rather similar layouts. The number of computers and screens differ depending on the current operation and number of employees working in these labs. In general, computer labs are located at the center of building and are usually surrounded by a number of offices. The total number of computer labs in D building is estimated to 12 i.e. three computer labs on each floor.

Depending on the business activity, usage of computer labs shows a variance, which also affect the power draw. The electricity demand of computer labs changes as the activity level and number of occupants present in the labs varies. Due to the uncertainty of these usage and possible changes during different timeframes of a year it is of high importance to observe and estimate the average energy demand in the computer labs. Measuring the typical energy consumption in computer labs can give possibilities to show in what extend the energy system is affected.

Two measurements on power demand on two computer labs with a representative size and magnitude was performed during a week in March. The method to measure the required power in a computer lab is based on logging the power supplied to a specific computer lab. Common for all computer labs is that the electricity is supplied from a dedicated canalis busbars located at each floor. The power demand is gathered by a measurement on the supplied current through each phase of these canalis busbars.

According to the result of the measurement, shown in Figure 8 and Figure 9, the average power supply in computer lab is around 2, 8 kW and 4,5 kW. As it can be seen the power draw is almost constant except during the working hours. These measurements show also that the power supplied during weekends and nights is relatively highly, which is a consequence of computers and screens are always on. The power supply during nights and weekends is calculated to be 85 % of the power supply that is required during working hours between 08:00-16:00.

-42-

Figure 8: The measured power needed in a computer lab during one week in March.

Figure 9: The measured power supply in a computer lab during one week in March.

To avoid possible deviations in the resulting power draw, additional measurements are performed in 4 additional computer labs, where the activity is expected to be more frequently and intense. Due to the fact that it is not possible to enter some of the existing computer labs in the building and the time limitation, momentarily measurements are conducted in 4 different computer labs. The result for power draw in these labs is shown in Table 2.

Table 2: The measured power demand to the computer labs and the total energy consumption in computer labs in D building.

Name of the computer lab Power demand [kW]

D3A 5,4

D3B 4,4

D3C 4,5

D2A 5,4

D2B 6,3

D4A 2,9

0

0,5

1

1,5

2

2,5

3

3,5

4

16:0

0:00

20

:30:

00

01:0

0:00

05

:30:

00

10:0

0:00

14

:30:

00

19:0

0:00

23

:30:

00

04:0

0:00

08

:30:

00

13:0

0:00

17

:30:

00

22:0

0:00

02

:30:

00

07:0

0:00

11

:30:

00

16:0

0:00

20

:30:

00

01:0

0:00

05

:30:

00

10:0

0:00

14

:30:

00

19:0

0:00

23

:30:

00

04:0

0:00

08

:30:

00

13:0

0:00

17

:30:

00

22:0

0:00

02

:30:

00

07:0

0:00

11

:30:

00

16:0

0:00

20

:30:

00

01:0

0:00

05

:30:

00

10:0

0:00

14

:30:

00

[kW

] Power demand of a computer lab

0 1 2 3 4 5 6 7 8

13:4

5:00

17

:30:

00

21:1

5:00

01

:00:

00

04:4

5:00

08

:30:

00

12:1

5:00

16

:00:

00

19:4

5:00

23

:30:

00

03:1

5:00

07

:00:

00

10:4

5:00

14

:30:

00

18:1

5:00

22

:00:

00

01:4

5:00

05

:30:

00

09:1

5:00

13

:00:

00

16:4

5:00

20

:30:

00

00:1

5:00

04

:00:

00

07:4

5:00

11

:30:

00

15:1

5:00

19

:00:

00

22:4

5:00

02

:30:

00

06:1

5:00

10

:00:

00

13:4

5:00

17

:30:

00

21:1

5:00

01

:00:

00

04:4

5:00

08

:30:

00

[kW

]

Power demand of a computer lab

-43-

Average 4,8

The average power to 12 computer labs

57,9

The measurements show a significant variance compared to the reference computer labs, where the initial measurements are conducted. The average power draw in one computer lab is 4,8 kW, which gives a total power demand of 57,9 kW for all the computer labs in the building. Assuming that the activity is constant throughout a year, the energy demand can be estimated to be 507 MWh per year.

6.1.2 Fan coils In each computer lab, a number of fan coils are used for regulation of process and comfort cooling of the space. The cooling is projected to balance the heat rejected from computers and the heat is absorbed in the brine water circulated in the fan coils. The fan inside the fan coils are driven by a motor that are in constant operation.

The number of fan coils differs depending on the layout of the space and the projected cooling demand. Usually 5 or 6 fan coils are installed at the ceiling above each computer lab, which adds up to 17 fan coils at each floor. Since the fan coils are identical, only three instant measurements are performed in order to decide the power draw to one fan motor. Similarly, the method is based on measuring the current through two phases supplied to a fan motor. Table 3 shows the result of the power measurements and the total power needed to fan motor in fan coils. The power load in all three measurements is approximately at the same level, which is around 100 W.

Table 3: The average power load to one fan coils, the number of fan coils and the total power requirement.

Measured power to one fan [W]

Number of fan coils in D-building

The power consumption to the fan coils [kW]

100 67 6,7

6.1.3 Cooling units in computer labs In addition to fan coils, 9 passive and active cooling units are installed in computer labs to reduce the generated heat load in these spaces. However, observation in these spaces showed that only 6 of these cooling units are activated. All these cooling units draw power from a power cabinet installed on each floor. The current supplied to two of these cooling units was measured in power cabinets. The average power and yearly electricity demand of 6 cooling units are shown in Table 4.

Table 4: The measured and estimated average power supply to the cooling units in computer labs.

Cooling units Measured power draw [kW]

Number of cooling units

Total power consumption [kW]

Annual energy [MWh/year]

A 2,2 - - -

B 2,3 - - -

Average 2,3 6 13,5 118, 3

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6.1.4 Server rooms Server rooms support daily activities and in total, there are 12 server rooms installed throughout different parts of the building. The number of computers, the capacity and configuration in each individual server room differs, based on the activity level. Basically, these rooms are devoted to a continuous operation of the computer servers and the capacity can be assumed to be constant. The electricity in server rooms is supplied to the servers and compressors and fans in the cooling units.

6.1.4.1 Servers The power supplied to the server originates from switchgear located in a small cabinet in the each server room. Measurements were conducted in five different servers were the power supply measured momentarily. To decrease the deviation of resulting power draw, measurements repeated three times during different hours and months in these chosen servers. Table 5 shows the result of the measurements on the power draw in servers. In total, only 5 different servers were accessible for investigation, which are used as a ground for further calculations. The power draw for remaining 6 servers is assumed to be the mean value of measured power supply to servers.

Table 5: The power load in five different servers during three measurements.

Server rooms Measurement 1 [kW]

Measurement 2 [kW]

Measurement 3 [kW]

MEAN power of servers [kW]

A 0,4 0,3 0,4 0,4

B 1,9 1,7 1,8 1,8

C 4,7 4,8 5,3 4,9

D 6,2 7,1 6,7 6,7

E 8,01 8,01 8,01 8,01

Mean value 4,4

One of the server rooms has a larger capacity and contains a higher number of servers, which also draw more power. Since measurements in this server room was not possible to be done, the power draw is assumed to be the mean value of the measured power supply to the servers. Based on the obtained information from interviews with employees, the power supply to the server is assumed to be 10 times higher capacity than the estimated average value of the power demand. The resulted power load in the servers is given in Table 6.

Table 6: The estimated power draw to the servers in D building

Power draw [kW]

Total power supplied to the servers in D building

91,6

6.1.4.2 Cooling units in server rooms Energy consumption in server rooms is highly affected by the predefined thermal sensitive conditions. In each of these rooms, there are one or in some cases more dedicated cooling units installed to maintain a stable temperature and humidity within the space, 24 hours a day. The cooling units are regulated depending on the temperature level measured by sensors in these units during operations.

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This temperature is compared to the set points and the cooling unit actives depending on the temperature difference between these two values.

Majority of the cooling units are installed during the last few years to provide an effective cooling. The working principle of the cooling units varies depending on if a unit involves a compressor in the refrigeration cycle. Cooling unit with a compressor is called active cooling that involves a refrigeration cycle, where the air is cooled through heat exchange in the evaporators. The compressors are regulated to initiate when the room temperature decrease.

As it mentioned before, one of the existing server rooms in the building is relatively larger and contains number of computers, which requires higher cooling capacity than a regular server room. Unlike the other server rooms, this room has 4 dedicated passive cooling units installed in the room. Passive coolers are using the principle of forced convection using a fan to maintain the heat transfer between brine water and room air in cooling coil. Fans in passive cooling units are assumed to work constantly since the load and capacity in previous section was assumed as constant.

Based on the assumptions in chapter 6.1.4.1 the servers are in constant operation, which also require additional cooling, thus the cooling units are also assumed to operate constantly. Since all the power is supplied though the main switchgear, measurements is based on monitoring the current in three phases and calculate the power draw according to Equation 8. In total the power supply to 5 active cooling units and 3 passive cooling units were measured. Table 7 & 8 present the power draw to the cooling units. Measurements include the fact that compressors initiate for a limited time of period and are usually turned off after a certain period of time.

Table 7: The measured power level in three passive cooling units in D building.

Type of cooling unit Server room Power consumption [kW] Average Power consumption [kW]

Passive cooling units

KA26 4,1

4,4 KA27 4,3

KA28 4,7

Table 8: The measured power supply to five active cooling units in D building.

Type of cooling unit Server room Compressor + Fan [kW]

Fan [kW]

Active cooling units

D146 6,6 1,6

D150 5,9 0,6

D252 6,2 1,0

D349 5,8 0,7

D355 5,5 0,7

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Average power consumption

6,0 0,9

The compressor in active cooling units is usually activated for a limited time and turned off when the room temperature reach a predefined set point temperature. To estimate the total energy demand of an active cooling unit it is necessary to monitor frequency of the operation time of the compressors. During one day the electricity draw to one cooling unit is logged to see the frequency of a compressors operating time. Figure 10 shows how the variations on the power supply to an active cooling unit. Generally fans work continuously and require a small amount of power all the time and require a average power draw on 0,9 kW. As the compressor start to operate the power supply for fans and compressors is around 5,2 kW. Including this fact of operation frequency, the compressors and fans are assumed to operate 66,6 % of the time during a year. During the remaining time only fans will be in operation.

Figure 10: The power needed to an active cooling unit in a server room logged during one day.

6.1.5 Pumps In general, the required pump power can indicate the amount of chilled water that circulates in each loop. All the existing pumps in the cooling system are regulated to operate at constant pressure. As a first step, it is useful to determine the volume flow in each pump to calculate the required power demand. Initially, the pressure development over each pump and power draw were measured in order to estimate the volume flow rate through chilled water loops. These inputs were used in Equation 4 to calculate the volume flow rate. The power consumption and pressure development in the pumps assumed to be constant. The measured power input, pressure development over chilled water pumps and the calculated volume flow in each pump are presented in Table 9.

Table 9: Measured power draw, pressure development and volume flow rate to the pumps in cooling system.

Power input [kW] Pressure development [Pa] Volume flow rate [m^3/h]

KB01 2,8 - 99,7

KB02 1,7 84000 46

KB03 2,2 - 63

KB04 2,4 65000 87

0 1 2 3 4 5 6

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

05

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

2017

-04-

06

[kW

]

The power demand to a cooling unit

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Considering that only a certain share of chilled water is directly correlated to the cooling demand within predefined system boundaries, the energy required to pumps should be based on this criterion. For pumps functioning in KB01, KB02, KB03 and KB04, the power input needed in server rooms and computer labs are estimated by using Equation 5 & 7.

6.1.6 Ventilation Ventilation in D building is controlled by three major AHUs, denominated to LA01, LA02 and LA03, are located at the top of the building. The primary function of these units is to provide ambient air in the air-conditioned spaces inside the building. According to the control system, the AHUs operate between 07:00-19:00 on Monday-Friday.

Computer labs and server rooms are usually located in diverse points of the D building and each of the labs requires ventilation with varying volume from the three existing AHUs. Generally, the regulation of air-handling unit’s is set to maintain constant airflow rate. In each computer labs, there are number of ventilation openings installed in a row with fan coils on the ceiling. Number of ventilation openings and the amount of ventilation flow in each space vary depending on several design criteria’s. The power supply to AHUs to maintain the ventilation requirements in the computer labs and server rooms are estimated using Equation 5 & 7. For this step, it is necessary to define the total airflow from AHUs and the airflow rate supplied in the computer labs and server rooms.

Airflow rate in the computer labs and server rooms are measured in different ventilation openings in 4 different computer labs. To detect the deviations the measured values are compared to projected values for airflow in these environments. The result of the measurements in the computer labs and the air-handling units are shown in the TABLE 10.

Table 10: The result of measured airflow rates in 4 different computer rooms from air handling units.

Computer labs Measured air flow rate [𝒎𝟑

𝒔] Projected air flow rate [𝒎

𝟑

𝒔]

A 0,48 0,31

B 0,21 0,34

C 0,18 0,27

D 0,26 0,33

Average 0,28 0,31

As it can be seen in Table 13, the measured values shows a variance compared to the projected values in these spaces. Differences are much higher in some computer labs, which needs to be adjusted to provide right amount of ambient air. The airflow rate in the server rooms is assumed to be the projected values given in the system draws and specification. The estimated total air supplied to computer labs and server rooms from AHUs are given in TABLE 11.

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Table 11: The total airflow rate supplied in the server rooms and computer labs.

Air conditioned area Air flow rate [𝒎𝟑

𝒔]

Server rooms 0,8

Computer labs 3,4

TOTAL 4,2

For calculation of the power needed in AHUs, the total airflow supplied from AHUs needs to be identified. The supply and exhaust airflow for each air-handling unit is measured momentarily, which is presented in Table 12. According to the estimated and measured values, the ventilation air needed in the computer labs is 37 %. In total, 46 % of all the air handled and transferred in to the building from air handling units is dedicated to the defined system boundaries.

Table 12: Supply airflow from the AHUs in the D building.

Air Handling Unit Supply air flow [𝒎𝟑

𝒔] Return air flow [𝒎

𝟑

𝒔]

LA01 2,3 3,2

LA02 2,9 1,7

LA03 3,9 3,0

TOTAL 9,1 7,9

Measurements on the power draw to all three air-handling units are assumed to be 32,4 kW (Malm, 2012). Despite the fans operating in the AHUs, there are number of compounds and control units that require a certain power as the AHUs are functioning. Taking into consideration these power-consuming factors, the power draw related to the airflow provided to the computer labs and server rooms are estimated to 11, 8 kW.

6.2 Refrigeration power Taking into account that not all the cooling is transferred only to the server rooms or computer labs, it is crucial to separate the cooling demand in the defined system from the common cooling system. In the following section the cooling demand in terms of refrigeration power is identified both for the whole system and for the cooling supplied to the components defined in the system boundaries.

6.2.1 The cooling system The cooling is successively transferred to the sub systems through closed chilled water loops referred as KB01, KB02, KB03 and KB04. A representative schematic figure over these loops and the system configurations of the existing cooling system in D building is shown in the Figure 11. Generally, cooling effect is delivered by heat exchange between cooling water in closed loops, which in turn is supplied to different cooling distribution units throughout the building.

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Figure 11: Description of the system configuration of the cooling system and associated chilled water loops.

The cooled brine water in the evaporator is circulated inside the loop KB01. A part of the brine water is directly sent to the passive cooling units in the computer labs. The rest and also the larger share of the brine water are divided into two different heat exchangers that absorb heat from chilled water loops in KB02 and KB03. When the brine water absorbs the heat from different circuits it returns to evaporator to complete the loop. The chilled water in KB02 supply is circulated in passive cooling units other spaces with high cooling demand. KB03 is the main circuit that provides cooling to the three AHUs in D building in order to ensure the set point temperature to the supplied air. Besides, a higher amount of chilled water inside KB03 continues to flow directly into KB04, which is the main circuit that deliver cooling to server rooms with active cooling units, fan coils inside offices and fan coils in the computer labs.

6.2.2 The cooling demand Refrigeration capacity supplied in to the entire cooling system in D building is estimated by measuring the temperature on the outer walls of the main pipes of the chilled water loops. As it described in Chapter 5.1, Equation 2 calculates the refrigeration power in KB01, KB02, KB03 and KB04. In summary, total refrigeration power supply to the computer rooms and server rooms and the fraction of the total cooling delivery based on the estimation of the volume flow rate and refrigeration power are shown in Appendix 1.

Undesired heat losses in the cooling system are a considerable part of cooling demand that should be taken in to consideration. Heat exchange capacity in the plate heat exchanger between the sealed loops was measured in order to determine the heat transfer efficiency. Using the estimated volume flow rates and inlet/outlet temperature between KB01 and KB02 and between KB01 and KB03, the efficiency is estimated to be around 0,85 as average for two heat exchangers.

6.2.3 Cooling demand of the fan coils It is generally sufficient to measure the volume flow rate of chilled water in a number of individual fan coils and determine an average volume flow rate delivered to all fan coils. This measurement is performed using a flow meter. In Table 13 the result of measured volume flow to five different fan

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coils located in computer labs are shown. Based on this, an average volume flow rate to a fan coil is assumed to be 0, 26 m3 per hour. To ensure the validity of the assumed average volume flow, the value is analyzed against the projected values given in system drawings of pipe and distribution systems for cooling. The average projected value is found to be 0, 13 m3 per hour, which is far lower than the assumed value.

Table 13: The measured volume flow rate of chilled water in the fan coils located in computer labs in D building.

Measured volume flow of cooling water to

fan coils in the computer labs [𝒎𝟑

𝒉]

Measurement 1 0,21

Measurement 2 0,41

Measurement 3 0,42

Measurement 4 0,13

Measurement 5 0,11

AVERAGE 0,26

As previously mentioned, the total number of fan coils in computer labs is 67. On average, the total volume flow rate is estimated to be 17,3 m3 per hour, which gives total required cooling of 26,1 kW that should be delivered from KB04. This cooling demand is assumed to be constant throughout a year.

6.2.4 Cooling demand in the server rooms A major portion of the cooling demand is used in cooling units in the server rooms. Since number of server, the electrical load and the cooled area shows variety in each server rooms, the cooling requirement had to be identified carefully. The amount of cooling water transferred to server rooms is measured on three active and two passive cooling units, which are presented in Table 11 with the corresponding values. In contrast to other cooling units, four passive cooling units usually process higher amount cooling water due to its low cooling efficiency. The average volume flow rate of cooling water and cooling effect for the active and passive cooling units are shown in the TABLE 14.

Table 14: The average volumetric flow rate of supplied chilled water and total refrigeration power to the cooling units in server rooms.

Volume flow of

cooling water [𝒎𝟑

𝒉]

Number of cooling

units

Total volume flow of

cooling water [𝒎𝟑

𝒉]

Refrigeration power [kW]

Active cooling units 1,2

11 13,3 20,2

Passive cooling unit 4,4 4 17,6 53,5

TOTAL 30,9 73,7

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6.2.5 Cooling demand in the computer labs Amount of cooled water used in these units is measured on two cooling units and this value assumed to be the same amount for the remaining 4 cooling units. Table 15 shows the volume flow rate of cooling water supplied and the total refrigeration power that is required for these units.

Table 15: The average volumetric flow rate of chilled water and the total refrigeration power to the computer units in the computer labs.

Volume flow of cooling water [m^3/h]

Number of cooling units

Total volume flow of cooling water [m^3/h]

Refrigeration power [kW]

Computer labs (Cooling units)

1,4 6 8,2 16,3

6.2.6 Cooling demand in the AHUs The cooling demand in the AHUs emerge during summer when the ambient air is over 19 ° C and the air needs to be cooled in order to ensure the pre-set supply air temperature at 19 ° C. The efficiency of rotary heat recovery in the AHUs is measured and calculated with Equation 9, which gives an average efficiency of 80 % for all three air handling units.

Based on these assumptions and calculations, the total refrigerant effect delivered from chilled water to the air in the AHUs is estimated to be 29, 1 kW. The total flow rate of supplied air in ventilation and in the system boundaries are discussed in detail in Chapter 6.1.6. For this particular case the rotary heat exchanger is assumed to not operate, since no heat recovery is needed when the ambient temperature is already over the set point temperature. The thermal energy removed from the air that is the required refrigerant effect that has to be transferred from the cooling water circulating in KB03 through the cooling coils. To be able to calculate the total cooling capacity for ventilation, the cooling element assumed to have an efficiency of 0, 8.

6.3 Chillers There are 3 chillers installed in the basement of the building that supply cooling for comfort and process cooling in D building. All three chillers are installed in 2015 in order to increase energy efficiency and reduce the energy demand in the building. Each week the order and the capacity of the operating chillers alter according to a schedule. Usually two of chillers operate simultaneously, one operates at the maximum capacity and the second one changes the capacity according to the demand requirement. Which one of these chillers acts primarily is decided based on number of operating hours. Regulation of the chillers is based on providing the set point of chilled water temperature at 6 °C that is distributed to the cooling system and is adjusted according to the return temperature of the brine water. Previous studies defined comfort cooling as the cooling demand associated with the cooling used to create satisfying thermal climate conditions for humans. Process cooling refers to maintaining the design criteria’s of temperature and humidity for specific practices such as in the cooling units (Karlsson, 2014).

It is necessary to identify the required power input to the chillers that generate the cooling in computer labs and server rooms but also in the building. During 8 days the power input to the one operating chiller (VKA02) that work with maximum capacity was measured. The total power draw to VKA02 is shown in Figure 12. Due to the limitation of not having enough measurement devices, the power input

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in the secondary operating chiller, in this case VKA03 is measured momentarily. To minimize deviation in the resulting power, measurements are repeated 6 times during different days and hours. The result of this measurement can be seen in Supplement 2. The resulted average power supply to VKA02 is estimated to be 70,8 kW. The secondary chiller VKA03 was working at an average of 55 % compared to the VKA02 and the average power supply estimated to 39,1 kW. Assuming that the power supply in the chillers is constant throughout the year, the total power draw can be estimated to 109,9 kW. This gives a COP2 at approximately 2,7.

Figure 12: The measured power input to the chiller, VKA02, during 8 days.

One observation in Figure 12 is that the power supply to the chiller increase remarkable during nights and weekends. Considering the low cooling and heating demand, it is probable that the cooling system is not functioning at an optimal level. Besides, low power supply is also detected in occupied hours could indicate that cooling demand is not directly correlated to the comfort cooling in the building. Another explanation to the increased power input is that chillers are primarily used to generate heating through heat sink in the condenser. In this concept cooling can be seen as by-product of the refrigeration cycle. The motivation of this procedure is the high price of district heating compared to prevailing electricity prices, which contributes to reducing amount of acquired district heating.

In section 4.4.5.1 the necessary cooling demand around the defined energy system was estimated to 145,1 kW. If the losses in the heat exchangers would be taken into account, the primary brine water loop KB01 should generate 167,9 kW to compensate diverse heat losses and ensure the process cooling in the computer labs and server rooms. The amount of power input to the compressors to generate the cooling demand in the system boundaries is calculated using the relation in Equation 1.

The variation of the total refrigeration power with the ambient temperature is presented in Figure 13. In this step, the refrigeration power generated in the chillers is based on the logged values from the control unit of the chiller system. The ambient temperature is logged for the same period of time by using a digital temperature sensor. Based on the monitored values the average refrigeration power is 294, 9 kW.

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Pow

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Power draw to the chiller VKA02

-53-

Figure 13: The refrigeration power as function of ambient temperature.

Using this relation between refrigeration capacity and the outdoor temperature, it is possible to investigate how the cooling demand changes with different outdoor temperatures during a year. For this step, the linear relation given in Figure 13 and the average ambient temperature in Stockholm were used to visualize this variation of cooling demand. Figure 14 shows that the climate independent cooling is around 280 kW, which also indicate the continuously demand of cooling mostly in the computer labs and the server rooms. Since these investigated areas could be affected by increasing outdoor temperature meaning that in some extend the process cooling is also climate dependent, the average required cooling is estimated to be an average value of cooling throughout a year. The average refrigeration power based on the Figure 14 is used as a base for the calculations is estimated to 296, 6 kW.

Figure 14: The variation of the cooling demand as a function of the average ambient temperature.

6.3 Result of the energy mapping This chapter shows the results on the energy mapping within defined energy system boundaries. By compiling the finding from the existing energy system and measurements, the prevailing energy use in system development environments is presented with the corresponding values. This is followed by the

y = 2,491x + 280,1

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proposed energy measures and the saving potentials developed by the measurements and the model set up from the qualitative result.

6.3.1 The electricity demand The key resource that is utilized to generate cooling is generally based on electricity the used for compressor operation in chillers. The electricity supply to energy system components and subsystems is presented in Table 16.

Table 16: The energy consumption in the defined energy system components in D building.

Energy consumption [MWh/year]

Computer labs 507

Fan coils 59

Cooling units (Computer labs) 118

Servers 802

Active cooling units (Server room) 411

Passive cooling units (Server room) 153

Pumps 32

Chillers 438

AHUs 37

TOTAL 2557

The proportion of energy consumed in D building related to system development environments is illustrated in the Figure 15. System development environments and related equipment including the cooling system components require 2557 MWh per year that is approximately 64 % of all the yearly electricity consumption in the D building. The highest energy demand based on the outcomes could be find in servers, which in turn require additional cooling from the cooling units. When the cooling related energy consumers are gathered in one category, the total energy consumption is the largest energy consumer, which is 30 % of the total energy demand in the building.

The category for unaccounted includes all energy consumer that is not identified within the system boundaries in this study. These are typical electrical equipment such as lightings, personal computer and diverse electronics, the rest of electricity demand to chillers, ventilation and pumps.

-55-

Figure 15: The energy consumption share between different components that are defined in the system boundaries.

6.3.2 Cooling requirements The evaluation of refrigeration capacity required in the existing system follows the given values in Table 17. The large share of cooling effect is mainly distributed to cooling units in computer labs and server rooms. Considering that the result does not include the cooling losses, this investigated cooling distribution systems utilize the major amount of cooling generated in chillers.

Table 17: The distribution units and corresponding amount of refrigeration power.

Distribution unit Refrigeration capacity [kW]

Fan coils 26,1

Cooling units in computer labs 16,3

Server rooms [Active cooling units] 20,2

Server rooms [Passive cooling units] 53,5

Ventilation 29,0

TOTAL 145,1

Comparing the produced refrigeration capacity in different cooling required spaces is illustrated in Table 17. Server rooms have a high demand compared to what is needed in computer labs and in the rest of the building. Computer labs require 19 % of the total refrigeration capacity. One thing that is important to point out is that the refrigeration power for the ventilation usually needed during summers.

Reviewing TABLE 16 and TABLE 17 show that approximately 73% of the power draw to the computers labs in is converted to heat, which in turn has to be cooled down by the cooling units and fan coils. The remaining heat is dissipated as transmission losses through the windows, doors and

20%

14%

11%

13% 3% 1%

1%

1%

36%

Energy consumption share in D building

Server

Cooling units (Server rooms)

Chillers

Computer labs

Cooling units (computer labs)

Chilled baffles

Pumps

AHU

Unaccounted

-56-

envelope of the building. In the server rooms approximately 79 % of the supplied power is dissipated as heat that needs to be cooled by cooling units.

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7 Energy measures In this section the potential energy measures that aimed to reduce the energy consumption within system development environment are evaluated. The goal is analyze the energy, economic and technical aspects as well as the consequences of potential implementation of each suggested energy efficiency measure.

7.1 Switch of the screens and computers during night The standard default setting for power options of computers in D building is set to never turn off the display and never put the computer in sleep mode. This default setting that is applied in the majority of the investigated computers at the facility as long as an individual power setting is not implemented. Similarly, neither of the computers used in the computer labs apply any power saving state. The major driving force for not using any power saving settings in computer labs is to ensure the continuous functionality and availability. Among the interviewed staff, the main concern of using power settings in the computers was the limited availability and flexibility, and potential delay of essential processes. Other concerns are related to the long starting time to wake up a regular computer. It was also mentioned that regularly shutting down computers would be inconvenient especially for sensitive electronic hardware such as for older computers.

During the energy survey in computer labs and interviews with different employees, it was found that the computer labs are in continuous operation approximately two months a year when the computers are running simulations. Otherwise the usage of the computer labs is limited to working hours. Another observation in these spaces was that some of the computer labs have much lower activity level compared to others.

The proposal in this context is to apply the most useful / adaptable power setting options during nights and weekends in order to reduce the power draw to the computers and related equipment. As most of the interviewed staff admitted, the usage of screens during unoccupied hours is often unnecessary and switching screens off could easily be implemented without affecting the workflow and computer activities. As it is described in Chapter 6.1, computers are not always used continuously, which would make it possible to partly apply “sleep mode” state. As a side effect of this reduced power draw, the heat load could also decrease considerably, which would require less cooling demand in these environments.

The average number of computers in a computer room is 31, while the number of screens is estimated to be 45. To avoid any deviations, the measurements are conducted on a number of computers and screens in different computer labs. Appendix 3 summarizes the measured values for power draw of different computers and screens in computer rooms. The reasons for using an average value of power draw depends on the high variety of size, model and age of the existing computers and screens that should be taken into consideration. Assumptions of the usage time and patterns are based on the gathered information from interviews with several employees as well as observations and measurements. The following assumptions are made in this step:

• All computers and screens run constantly throughout a year.

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• According to the interviewees, the computer labs are in constant operation for approximately two months in a year, which is assumed to be 8 weeks per year. The remaining time will be assumed to be in operating in working hours.

• Approximately 40 % of all screens are installed with the setting to turn off after a certain time period.

• Based on the calculations in the previous section, approximately 73 % of all the electricity supply to the computer and screens is converted to heat, which in turn should be removed by the cooling units and fan coils.

• As the heat load reduce and the power settings are implied, the cooling units and fan coils will gradually turn off.

• A usual working hours at the facility is 08:00-16:00. • The power options are implemented during nights (16:00-08:00) and weekends.

Since only a small number of computer labs could be investigated, the calculated average power draw is not weighted with consideration to the uncertain usage frequency of computers and screens.

7.1.1 Cost

In this measure it is assumed that alternating the power settings does not involve any cost since these settings already exist among the conventional computer power setting options. Implementing this type of measure will also require programming for different cooling distribution components to match the altered specifications and cooling need. To adapt the cooling components after the desired refrigeration capacity, diverse programming and control applications have to be arranged. The cost of these programming and installation is assumed to be 50 000 SEK.

7.1.2 New energy demand

As a consequence of the power reduction and heat development in the computer labs, the cooling demand is assumed to decrease gradually. This is a direct result of the temperature drop of the returning cooling water, which in turn requires reduced volume flow rate of cooling water and less power input to the pump. Finally, chillers will also operate at a lower capacity and the power consumption in the compressors will decrease.

7.1.3 Result

Table 18 shows the electricity consumption of computers and cooling system components when different power setting options are implemented. As expected, one of the biggest energy reductions depends on reduced electricity to computers and chillers. Initially, the cooling units were assumed to turn off since fan coils in these environments have the capacity to meet the cooling demand. Activating the power saving option to turn off screen during unoccupied hours generate a saving of approximately 149 MWh/year. If the power setting option “sleep mode” could be implemented in 25 % of the computers along with that all screens could be turned off during nights and weekends, the total saving is calculated to 273,6 MWh per year compared to the current situation.

Table 18: The power reduction in computers and related cooling system components is illustrated with related cooling demand by implementing different power settings in the computer labs. The economic model is also presented for estimated PP and LCC.

Energy consumption [MWh/year]

Computer and screens

Chillers Pumps Cooling units and fan coils

Reduction of energy demand

[SEK/year]

Payback time

[year]

LCC [SEK]

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Current situation 507,1 156,9 12,9 177 - - 6 990 000

Turn off screens 390,5 127,1 10,3 177 148,9 0,3 5 780 000

Disconnect screens 372,0 122,4 9,9 177 172,6 0,3 5 590 000

25 % of the computers in sleep mode and turn off screens

350,3

118,4

11,0

100,6

273,6

0,2

4 770 000


309,9

105,5

9,7

90,4

338,4

0,2

4 230 000


229,5

79,7

6,9

76,3

461,5

0,1

3 240 000

Disconnect all the computers and screens between 16:00-08:00 & weekends

158,6

58,4

4,7

62,7

569,4

0,09

2 360 000

If the energy savings related to the cooling reduction such as chillers, pumps, fan coils and cooling units are summarized in one category than the calculated energy saving by turning off screens in unoccupied hours is 169 MWh/year. Reviewing Table 18, the highest potential of energy saving comes by avoiding unnecessary usage of computers. Since, the electrical equipment tends to consume power when they are plugged, disconnecting computers and screens gives substantial benefits. Measurements showed that screens consume approximately 14 % of the power draw compared to the idle mode even when they are turned off. To avoid waste energy the screens could be disconnected, which could save additional 18 MWh per year.

In Figure 16, the total energy saving for cooling system components, namely, chillers, pumps, fan coil and cooling units are merged in one category to address the reduction of energy in in terms of cooling and electricity. Since the large amount of cooling is essentially used in server rooms the cooling demand does not decrease as radical as in the power reduction in the computer and screens.

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Figure 16: Energy consumption level with changed power settings in computers in system development environments. Along with the power reduction of the computers, the total energy usage for cooling demand is categorized for different power setting options.

7.1.4 Discussion

Based on the result, the energy measure shows the potential energy saving options by implementing available system adjustments. However, this is highly dependent on the willingness of the managements and employees and on the technical probabilities. The most essential contribution of this measure is to emphasize the importance of reducing the waste energy utilization in electronics and related cooling.

However, this option could have many technical limitations when it comes to the required time of starting a computer or technical specifications. Restrictions on availability and various personal requests can strongly limit implementations of these types of energy measures. Considering other types of reactions such as experienced stress and delayed work deliveries this measure requires very careful implementations so that it would not affect workflow or experienced comfort.

According to the staff working in these environments it is not always possible to turn off or put the computers to sleep mode, due to system connections or other technical applications. An additional limitation of this measure occurs if the older computers are taken in to consideration, since these computers could be damaged by sudden changes in power. However, if a central control of power settings for these computers is not an option, than an adaptable solution could be to manually implement this energy efficiency measure on computers and screens.

Current consumption

Turn off screens between

16:00-08:00

Disconnect screens

25 % of the computers in sleep mode

50 % of thecomputers in sleep mode

100 % of the computers in sleep mode

Disconnect computers and screen between

16:00-08:00

Computers 507,1 390,5 372 350,3 309 229,5 158,6

Cooling 346,8 314,4 309,3 230 205,6 162,9 125,9

Total 853,9 704,9 681,3 580,3 514,6 392,4 284,5

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7.2 Installing new fan coils in the computer rooms It was found that the temperature of the supplied ventilation air in the computer labs was higher than the temperature set point, which is set to 19° C. This situation is also confirmed by the logged values from the central control system for LBA02, where the supply air temperature into the building was in the most cases over 19° C with an average value on 19,85 °C (see Figure 17). The average air supply temperature from all three air handling units is estimated to 19, 35 C, while this value in computer rooms is measured to 19,53 °C. As the supplied airflow goes through the ventilation channel, the air is heated due to friction and heat exchange with the surroundings. As mentioned before, there are also complications with the unbalanced air supply in the computers labs, which in some cases is lower or higher than the projected values given in the system specifications.

Figure 17: The temperature of the supplied ventilation air from LBA02 in D building.

To analyze how the air temperature changes during different time intervals in computer labs, air temperature in 4 different computer labs is logged with a temperature logger. These measurements took place during different time periods between February and March that last for 4-7 days. Figure 18 presents the result of these measurements, where each line illustrates the logged air temperature in one computer lab respectively. Average air temperature in the computer labs is estimated to 22,9 °C. The result shows a clear variety during occupied and unoccupied hours, where the indoor temperature changes between 21,6 - 25,2 °C.

Figure 18: The logged indoor temperature in computer rooms.

17 17,5

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Air temperature in 4 diffrent computer rooms

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However, ventilation systems in the building provide the pre-set standard levels on volume flow rate and temperature of ambient air at different points of the building. In general, the incoming ventilation air increases the heat loads in computer labs, which has to be removed by fan coils and cooing units. An alternative solution to reduce the heat loads in these spaces is installing integrated comfort modules or fan coils. In this concept, the ventilation air will be supplied through a cooling battery that is installed inside of the ventilation openings. Basically, the fan coils will have a similar function as the existing fan coils in computer rooms, which integrates the ventilation air and cool it before the ventilation air enters the computer rooms. One of the presumptions is that the unbalanced airflow rat e from ventilation is corrected to provide the projected amount of air.

7.2.1 Costs

The required cooling capacity in this unit should be projected to provide at least the same refrigeration capacity as in the cooling units in order to exclude the usage of cooling units located in computer rooms. In addition to the initial cost of the units, this measure requires modifications of the air distribution channels and pipes configurations that bring in installation and labor costs.

Observations and measurements showed that in some of the computer rooms heat load is higher than others. Basically, this situation depends on the number of computers, the number of occupants and the activity level in these rooms. To compensate this diversity in cooling demand, two different proposals will be presented. In the first proposal fan coils will be installed in the rooms that are assumed to have higher heat loads. The location of the computer rooms and the number of proposed fan coils are shown in Table 19. A second alternative to the first proposal is the installation of fan coils in each computer room for potential changes in the future.

Table 19: The location and proposed number of fan coils in the computer labs.

Number of fan coils

Level 1 2

Level 2 1

Level 3 3

Level 4 1

TOTAL 7

Based on the number of cooling units the refrigeration power and cooling water volume flow rate is calculated according to given values in Table 20.

Table 20: The number of fan coils and required effect and volumetric flow rate of chilled water for 2 proposals.

Total number of units

Total refrigeration power [kW]

Total cooling water volume flow rate [m^3/h]

Proposal 1 7 17,5 4,7

Proposal 2 12 30 8,1

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The difference of the inlet and outlet temperature of the cooling water in the fain coils is assumed to 3 K. Technical specifications of different products on fan coils require chilled water temperature at 6-12 °C. This can be provided from the same pipe connections from KB01 that currently providing cooling water to the existing cooling units. In addition to these assumptions, the power draw to the new fan coil is assumed to be 150 W. The expected yearly energy consumption to the new fan coils is shown in Table 21. Table 21: The estimated power draw and annual energy consumption of the fan coils.

Proposals Power draw to one unit [W]

Total power draw to fan coils [kW]

Total energy demand [MWh/year]

Proposal 1 150 150*7 =1,1 9,2

Proposal 2 150 150*12 = 1,8 15,8

This energy measure doesn’t bring a necessity to arrange major modifications in the connection point of pipes delivering cooling water. In this case, it is possible to use the existing pipes linked to KB01 with small installations in the baffles. One important aspect of this proposal is that the refrigeration power is higher than what cooling units in computer labs are providing in the current situation. As an effect of this higher cooling capacity, the demand of refrigeration during nights is eliminated. This means that when AHUs are not operating, only fan coils and the fan coils will have enough capacity to provide cooling in these spaces. Further costs will originate from the potential correction and removal of the existing components during the installation of new fan coils. Evaluation of costs for instance the initial price of fan coils, installation and labor costs as well as technical specification are based on interviews or personal contacts with different companies (Kylma, 2017) & (Swegon, 2017). Initial investment that is required for these suggested measures are presented in Table 22. Table 22: Initial cost of purchasing new fan coils and labor and installation costs for the suggested proposals.

Initial cost [SEK] Labour and installation costs [SEK] Investment [SEK]

Proposal 1 10 000 * 7 = 70 000 70 000 140 000

Proposal 2 10 000 * 12 =120 000 120 000 240 000


Savings related to this measure are eliminating the cooling units and the refrigeration power that are delivered through KB01. Initially, the electricity draw to the existing cooling units is the most potential saving option. As a result of this, the cooling water could be reduced, which gives lower pump power and reduces the required refrigeration capacity generated in the chillers. Total saving potential in form of energy and momentary terms is presented in Table 23. Proposal 1 indicates the same amount of refrigeration capacity that should be generated in the chillers, which does not lead to any savings in power input to the compressors in the chillers. When it comes to proposal 2, the required volume flow rate of chilled water can be met by the existing pump specifications. However, since the heat exchange in the new fan coils is assumed to have higher efficiency, the required cooling demand from chillers will be higher, which result in additional costs and power input in the chillers.

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Table 23: The estimated energy reduction of the suggested proposals.

Proposal 1 Energy reduction [MWh/year]

Cooling units 118,3

Pumps 0,9

Chillers -

TOTAL 119,2

Proposal 2 Energy reduction [MWh/year]

Cooling units 118,3

Pumps -

Chillers -38,8

TOTAL 79,5

7.2.3 Result

Summing up the economic consequences of this proposal gives a payback period of 1, 3 years for Proposal 1 and 3,8 year for Proposal 2. The yearly maintenance cost of this proposal is estimated to be 2000 SEK. Accumulated savings, costs and initial investment of equipment are presented in Table 24.

Table 24: Summarized life cycle costs, savings and payback time for the proposals.

Investments [SEK] Saving [SEK/year] Payback time [year] LCC [SEK]

Proposal 1 140 000 110 000 1,3 713 000

Proposal 2 240 000 63 700 3,8 1 280 000

7.2.4 Discussion

One of the main benefits in this energy measure is that combining the ventilation and fan coils in the same unit to keep the system more compact, which in turn gives the possibility to reduce potential failures, and increase cooling capacity in the system. In addition, the incorrect operation of the cooling units could be revised by replacing them with fan coils, which benefits on increased refrigeration capacity as well as decreasing the redundant heat load from air conditioning. This will have an additional advantage by effectively removing the heat load from the computer rooms. Besides, this measure does not require major installation in the existing distribution system and has short payback time. It is also possible to install the fan coils in the most required areas in order to increase refrigeration capacity.

Eliminating the cooling units and installing fan coils includes the risk of reduced refrigeration power in these environments. Currently, the cooling units provide cooling through the floor and could have an essential effect on the thermal forces. Validation of potential implementations and resulting effects should be carefully investigated to adapt to the specific needs in these rooms. During the convective

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cooling in the fan coils the condensation risks of the ambient air is also a crucial design factor that has to be taken in to consideration.

7.3 Lower the set point of supply air temperature in AHUs Instead of installing new fan coils in the computer rooms that require capital-intensive investment, the supply air temperature in the AHUs could be directly reduced in order to minimize the heat load from ventilation. Compared to the previously suggested measure, this is a central control option to control the supply of ventilation air. In this step, the supply ventilation or temperature will be reduced to 16 °C. As it mentioned in the previous chapter, approximately 0,5 - 1 °C heat is added to the ventilation air. This is due to friction in the ventilation channels, pipes and fans as the ventilation air flows through and distributed to different spaces in the building.

7.3.1 Cost

Since all the AHUs are regulated from a central control system, reducing air temperature involves programming and setting of new conditions. This cost is assumed to be 6 hours work, which requires 3000 SEK. However, additional costs can appear, as the cooling demand to the air is estimated to be higher especially during summers. To generate the additional cooling demand, the chillers require 14,7 MWh per year and the energy demand in pumps will be 1, 7 MWh per year.


This energy measure, eliminate the usage of a certain amount of district heating since heating effect is needed in order to heat the air that is reduced from 19 °C to 16 °C. The yearly net cooling and heating consumption for the current and the proposed energy measure are shown in Table 25. Efficiency for the heating and cooling coils are assumed to 0,8.

Table 25: The yearly energy saving for cooling and district heating demand compared to the current situation.

District Heating [MWh/year]

Energy saving 20,3

By adding the supplementary refrigeration power in these spaces, it will be possible to phase out some of the current cooling distribution system components. This generates savings in terms of electricity and cooling capacity. Consequently, the room temperature will be lower and requires less refrigeration capacity during unoccupied hours. For instance the usage of cooling units during hours when the building is ventilated could be avoided, which also entails less refrigeration capacity demand and electricity. The estimated savings from in terms of electricity in different components are presented Table 26. New conditions are calculated to result in 20, 3 kW refrigeration power, which provides higher capacity than cooling units.

Table 26: Yearly energy saving in pumps, chiller and cooling units by reduced set point of supply air temperature in air handling units.

Savings [MWh/year]

Cooling units 42,1

Pumps 1,9

Chillers 23,6

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District heating 20,3

TOTAL 87,9

7.3.3 Result

Table 27 shows that the payback time of this measure is low and includes a high potential to savings for potential in case of implementations.

Table 27: The economic impact of reduced set point of supply air temperature, in air handling units in D building.

Investments [SEK] Saving [SEK/year] Payback time [year] LCC [SEK]

3000 65 800 0,05 136 300

7.3.4 Discussion

This model is a more centralized and effortless control option compared to the proposed energy measure in Chapter 7.2. One of the drawbacks of this model is related to the unaccounted effects on reduced supply air temperature in offices and other spaces. Reducing temperature can slightly decrease the room temperature in these environments as well. In this case, the heating demand could increase, which can reduce both savings and payback time in for this model. This energy measure does not require any modification or installation of the existing cooling system, which make this measure feasible.

7.4 Night cooling A natural way to cool computer labs is to use the cold ambient air and lead it in to the building, where it could be used. The weather conditions in Sweden allow to applying of cold ambient air without using chiller to supply of cooling. The average air temperature in Stockholm is below 5 degrees Celsius and it is relatively common that the temperature drops under this level during nights. This concept suggests transferring the ambient air in to the computer labs through existing air handling units during unoccupied hours (19:00 pm and 07:00 am on weekdays and weekends).

To meet the cooling demand in the computer labs the new supply air temperature is set to 15 °C. One crucial design parameter in this measure would be to change the default temperature level from 15 °C to 17 °C during summers. This is based on avoiding the risk of condensation within the air-conditioned spaces that cause damages on the electronic devices.

7.4.1 Cost

This energy measure would obviously set new electricity requirements on the AHUs that usually are out of operation between 19-07 and weekends. The fan, pumps, control system and other associated equipment installed in the AHUs determine the power consumption level. The ventilation airflow is set to be 50 % higher than the current airflow (3,39 m3 /s) to the computer labs. This is to overcome potential friction losses in the ventilation distribution system. The power draw of one of the existing units has been measured to calculate the power draw for this measure. To obtain an accurate value, the power draw of irrelevant fans and pumps for the new conditions is neglected. A summary of the new electricity requirements on the AHUs is illustrated in Table 28.

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Table 28: The estimated power draw in the AHUs in D building according to the new operation conditions.

Power draw of one AHU [kW]

Total power draw of AHUs [kW]

Total energy demand [MWh/year]

6,892 23,197 101,604

This energy measure requires the installation of new pipes for the ventilation system as well as dampers that can be regulated to open/close according to the new settings. Since there is no usage of ventilation air when no employee is in the building the new arrangement of ventilation will be supplied only to the computer labs for cooling purposes. Besides, the refrigeration power needed can be optimized by adjusting the supplied air to a lower temperature level and by increasing the amount of supplied ambient air. Thus, the cooling demand on the chillers and the cooling capacity from the cooling units in computer labs can be reduced.

Another cost will emerge with the district heating, when the ambient temperature is low and the heat exchanger is not able to recover the necessary heat to supply air. Estimations on the effect of the district heating is done by considering the average ambient temperature in Stockholm and the efficiency of the heat exchangers in the AHUs. As it mentioned before, the heat exchanger efficiency is assumed to be 80 %. The price of district heating is calculated by using an average value of the last three years invoice for district heating at the facility. The calculated district heating demand and its cost are shown in Table 29.

Table 29: The estimated district heating demand and cost for night cooling through ventilation.

District heating [MWh/year] Price [SEK/MWh] Cost [SEK/year]

38,5 722 27 800

A list of the requirements for the required materials and labor cost for installation are presented in Table 30. The price setting on the general cost is estimated by consulting different companies and manufacturers working in relevant businesses.

Table 30: The investment costs for installation and other required components.

Price [SEK] Source Number Cost [SEK]

Damper with actuator

5100 (Lindab, 2015) 12 61 200

Circular duct (Ventilation system)

400 SEK/ 3 meter

(Ventilation & Sotning i Täby AB)

350 m 140 000

Installation 600 SEK/hr (Ventilation & Sotning i Täby AB)

120 h 72 000

Programming 635 (Swegon, 2017) 40 h 25 400

TOTAL 298 600

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By changing the cooling supply source from chillers to the ambient air, saving in terms of electricity and cooling effect can be achieved, which is presented in Table 31. With these new settings, the cooling units in the computer rooms and fan coils can be turned off during nights. This could generate profits through reduced power supply to the pumps and reduction of the generated amount of refrigeration power in the chillers.

Table 31: The reduction of energy in the ventilation by implementing night cooling through ventilation.

Energy reduction [MWh/year]

Cooling units 59,2

Fan coils 29,3

Pumps 6,3

Chillers 76,3

TOTAL 171,1

7.4.3 Result

The resulting savings with estimated payback time based on the assumptions are presented in the Table 32. According to the parameters the variable costs and revenues give a saving of 41 767 SEK per year that allow a payback time of approximately 7, 2 year.

Table 32: The summarized investment, life cycle costs, savings and payback times for the energy measure night cooling.

Investments [SEK] Saving [SEK/year] Payback [year] LCC [SEK]

298 600 41 700 7,2 1 430 000

7.4.4 Discussion

One of most important outcomes of this measure is the possibility of using free cooling, which decrease the dependency on the cooling generation in the chillers. A key benefit is the utilization of natural sources such as cold ambient air instead of using electricity that can be seen as environmental friendly option.

One of the major concerns is, however, the night cooling could set several complexities such as the programming of dampers, cooling units and fan coils. The regulation of several components may increase the risk of potential failure. Keeping a system simple and compact is preferable than using several and complex components.

Since the AHUs and distribution channels are arranged to supply higher capacity in the building, the calculated airflow rate in this measure may be too low to reach these environments during nights. In addition to the risk, there are other losses such as friction, pressure and leakages that will result in lower supply of airflow than projected. Other issue with this proposal is the high investment cost and

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long payback times. Due to the added complexity to the system the estimated investment could be higher in reality than the estimated value.

7.5 Demand controlled cooling in computer labs The cooling in computer rooms is generally regulated with pneumatic thermostats that are manually controlled. It is a closed loop control design that is responsible for maintaining the system temperature near to the desired set point of room temperature. Depending on the changes in the desired temperature, a pneumatic actuator responds to pressure changes and regulates the amount of cooling water in the fan coils.

An observation showed that the thermostat was adjusted to the minimum level of cooling at 16-17 °C, although the computer lab was recently removed and no cooling demand was required. This indicates the need of an automatic control system that can adjust the cooling demand by sensing the room temperature. A simple way to correct this is to change the existing pneumatic actuator and thermostats with a new electronic or digital thermostat.

7.5.1 Cost

Changing the thermostats entails cost in terms of investments for the acquisition of a new actuator, adjusting the required programming and installation. The price of the new electronic/digital thermostat is assumed to be 3 000 SEK, while the installation and programming is assumed to be 2 000 SEK in total. In addition, the yearly maintenance cost of this proposal is estimated to be 2000 SEK.


Replacing the pneumatic thermostat will generate saving as this option limits the unneeded usage of chilled water and power draw to the chillers and pumps. The estimated saving potential of this proposal is shown in Table 33. Measured volume flow rate and refrigeration power to a fan coils was mentioned in Chapter 6.2.3.

Table 33: The estimated saving potential from chiller and pumps by replacing the pneumatic thermostats.

Component Energy saving [MWh/year]

Chiller 8, 8

Pumps 2,0

TOTAL 10,8

7.5.3 Result

The summarized result of savings, cost and payback time follows the given values in Table 34. Since this measure does not lead to any variable costs, the payback back time will be around 6 months.

Table 34: The summarized investment costs, savings and payback time by replacing the pneumatic thermostat in the computer lab.

Investments [SEK] Savings [SEK/year] Payback time [year] LCC [SEK]

5 000 10 800 0,5 20 400

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7.5.4 Discussion

Compared to other proposals, this measure is relatively easy to implement that could generate immediate benefits. More than finding a solution to the necessary cooling in computer rooms, in this case the saving originates from reducing the waste energy in the cooling system. These types of small adjustments and detailed investigations on the efficiency of the other pneumatic thermostats should be investigated to maximize the potential savings.

7.6 Installing a separate AHU for computer labs Free cooling could be an economical method for utilizing cold outdoor temperature that can be used to assist or replace the chiller system. When the outdoor temperature is relatively lower than the indoor temperature, the air conditioning system could utilize cold ambient air as a free cooling source. The concept could partly or completely replace the conventional chiller system by providing the same amount of cooling effect. The existing central air distribution system have its limitations when it comes to use free cooling for reduction of the power draw to several cooling associated units, which is described in Chapter 7.4.

To minimize the cooling demand in the computer labs, an additional air handling unit could be installed that will be specified to serve only in the computer labs. The supply air temperature and air volume flow rate will be regulated according to occupancy rate, working hours, seasonal conditions and cooling demand. To achieve the supply of the right refrigeration power and reduce the dependency on chillers, the volume flow rate of air will be increased compared to the current level. In order to keep satisfying thermal indoor conditions, the supply air temperature from the new air handling unit is assumed to be 17 °C during working weeks. To maximize the refrigeration power the supply air temperature from ventilation will be reduced to 15 degrees during nights and weekends.

7.6.1 Costs

An expected cost generation of this measure is the initial investment cost of the air handling unit, programming, installation and labor costs. Information regarding the price is set by contacting a company about specific requirement on the installation as well as reviewing the existing products and associated technical specifications (Fläktwoods AB, 2017). Table 35 presents the fixed costs for different components that are needed for this installation and programming.

Table 35: The share of investments regarding installation of a new AHU for computer labs.

Price Number Cost [SEK] Source

Investments on AHU 300,000 1 300,000 (Fläktwoods AB, 2017)

Installation costs 100,000 - 100,000 Fläktwoods AB, 2017

Labour cost 100,000 - 100,000 Fläktwoods AB, 2017

Programming 635 40 h 25, 4 (Swegon, 2017)

TOTAL 525,4

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Another type of cost emerges as AHU start to operate. Supply of constant air ventilation requires power draw to the fans and pumps. Chilled water and district heating will be needed to meet the air temperature at the desired level. These estimated costs for power draw, and district heating demand and costs associated to cooling delivery are shown in Table 36.

Table 36: The estimated variable cost related to the installation of new air handling unit.

Cost [MWh/year]

Power draw 113,9

District heating 28,8

Pumps 9,4

Chillers 8,0

TOTAL 160,1

In addition, the yearly maintenance cost of this proposal is estimated to be 10 000 SEK. Since the AHU is usually in operation for at least 10 years, the final value of AHU after 10 years is assumed to be 50 000 SEK.


Since the AHU is expected to deliver the total cooling demand, current cooling units and fan coils will be gradually phased out. This solution will give savings with reduced power draw to pumps and compressors, reduced district heating and refrigeration power from chillers. Table 37 show the estimated savings for different cooling related equipment.

Table 37: The potential savings from cooling units and fan coils as well as reduced refrigeration power and reduced power demand.

Energy savings [MWh/year]

Cooling units 118,3

Fan coils 58,7

Pumps 12,6

Chillers 152,6

TOTAL 342,2

7.6.3 Result

Including all the investment, variable costs and potential savings the calculated payback time are shown in Table 38. The quantitative result points out clear savings that ensure a payback time of 2 years and 11 months.

Table 38: The summary of the estimated initial and life cycle costs, saving potential and the expected payback time.

Investment cost [SEK] Saving [SEK/year] Payback [year] LCC [SEK]

525 400 182 100 2,9 1 870 000

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7.6.4 Discussion

Similarly to the previously proposed energy measure in Chapter 7.4, this proposal can be seen as an environment friendly option. With the chosen technical features, this measure has a more homogenous and comfortable distribution of cooling within computer rooms. Today, a number of cooling units located in computer rooms are blocked or are regularly shut down by the employees. Cooling from the ventilation openings will also reduce the risk of blocking these units and achieve a better cooling effect in these environments.

According to Boverket´s regulations the lowest operative temperature in air-conditioned occupancy zone is 18 °C for offices. Besides, the directed operative temperature differences in different points of the spaces should not exceed 5 Kelvin (Boverket, 2015). An important presumption in this proposal is that once the AHU starts to operate, the room temperature is reduced to a certain level since the refrigeration capacity is enough to remove heat load from electronic devices. Installing a new AHU, gives possible improvements to arrange efficient exhaust air duct that stimulates higher air exchange and faster discharge of the warm indoor air. In addition, it would also be possible to regulate the temperature and airflow rate based on the demand in the computer room, which in turn gives possibility to fulfill the general requirements of thermal standards.

The proposal can require additional projections to fit the cooling systems in the buildings. An issue, related to the ventilation is over ventilation that can have undesired effects for occupants in computer rooms and offices. This measure can lead to additional heating demand in the offices since the computer rooms are not completely insulated from the offices.

7.7 Change the location of the computer labs One of the obvious obstacles for effective cooling in the computer rooms is their location. Computer labs are usually open spaces that are surrounded by a number of offices that, in most cases are constantly heated. Temperature regulation in offices often affects the amount of refrigeration power that is needed in computer rooms. In addition fan coils are installed under the ceiling of the computer rooms. The heated indoor air is usually accumulates between the two ceiling walls and is partly cooled down by fan coils. The remaining indoor air is transported to an exhaust air channel and is transferred to the AHUs for heat recovery.

Due to the long distance between exhaust air ducts and computer rooms and the weak intake capacity of the fans, it can take long time to completely exchange of the indoor air. Consequently, the return air heats up the space gradually and generate additive heat loads in the computer rooms. The direct effect of this structure makes these rooms insulated from the exterior envelope of the building and makes the warm indoor air difficult to leave the system.

All building structures include the risk of air leakage or infiltration through walls, roofs, doors and windows. In such climate zones, where the average ambient temperature is relatively low occupied area should be heated for a certain time period. This is due to a large portion of overall heat losses that is dissipated from the building structure. Considering the high heat loads that constantly generated in

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computer labs from the computers and screens, this could be used to maintain a thermal comfort in a more natural way by increasing the transmission losses.

Three temperature loggers were located in different office rooms at three different floors in order to estimate the average temperature level in offices. The gathered data of the logged temperature values is shown in Figure 19 and the average temperature in the offices is estimated to be 22, 7 °C. This pattern shows that the surrounding ambient temperature in offices can partly affect cooling in the computer rooms that increases the heat loads and delay the refrigeration power.

Figure 19: The logged indoor temperature in 3 different offices during 8 days.

Investigations of the best location for computer labs in relation to cooling load are conducted with help of the software “Swegon ESBO Light”. For this step, two scenarios with four different directions are simulated (see Table 39) by using the available information of the technical properties in the building and the collected values for the existing cooling system. Detailed information and input used in this simulation is given in Appendix 4. The idea in this simulation is to investigate if the location of computer labs could affect the cooling needed.

Table 39: The simulated scenarios with different direction and characteristics of the walls.

Scenario Direction of computer lab facing

Building inner walls -

One exterior walls (with a window) North, South, West, East

Two exterior walls (with a window) North, South, West, East

7.7.1 Cost

In terms of cost, the implementation of this proposal could create major modifications of the size and location of the rooms, installation of new cooling system equipment and other potential corrections. For this reason and the uncertain amount of expenses of this proposal, cost generation is not included in this measure.

16

18

20

22

24

26

28

3-21

-201

7 0:

00

3-22

-201

7 0:

00

3-23

-201

7 0:

00

3-24

-201

7 0:

00

3-25

-201

7 0:

00

3-26

-201

7 0:

00

3-27

-201

7 0:

00

3-28

-201

7 0:

00

3-29

-201

7 0:

00

3-30

-201

7 0:

00

Tem

pera

ture

[°C

]

The office temperature

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Table 40 shows the result of the simulation with given assumptions. The cooling demand shows variation as the orientation and locations changes, which is shown in detail and corresponding values in Appendix 4. The result shows the highest possible reduction of the cooling demand with the given parameters, when the rooms are orientated towards South and have two outer walls (one wall with windows). The power demand is calculated by assuming a constant cooling requirement throughout a year.

Table 40: The result of the simulation that states the energy and power demand all three scenarios.

Scenarios Orientation Cooling demand [MWh/year]

Current cooling demand - 371,2

1. Building inner walls - 87,7

2. One exterior walls (with a window) South 43,0

3. Two exterior walls (with a window) South 40,8

The savings in terms of cooling that is generated and distributed through the cooling system are presented in TABLE 41. As Table 41 shows, the cooling demand reduces remarkably when location and surrounding characteristics of the computer labs changes. This makes it possible to phase out the cooling that is generated from cooling units and to turn off a fan coils in each computer room and still deliver more than necessary cooling. Thus, the volume flow rate of the cooling water transferred from the pumps and chillers will be lower than the current level. The following simplifications are used for calculation of saving potentials in each computer lab to meet the new cooling demand:

Scenario 1: Eliminate cooling units and one of the fan coils

Scenario 2: Eliminate cooling units and two of the fan coils

Scenario 3: Eliminate cooling units and two of the fan coils

It should be pointed out that although a considerable part of the cooling equipment is eliminated, the remaining fan coils will have almost 3 times higher cooling capacity than necessary refrigeration power in the Scenario.

Table 41: The estimated saving from reduced energy to pumps, chillers, cooling units and fan coils by changing the location and orientation of the computer rooms.

Scenario 1 Scenario 2 Scenario 3

Pumps [MWh/year] 3,9 5,8 5,8

Chillers [MWh/year] 70,7 88,6 88,6

Cooling units [MWh/year] 118,3 118,3 118,3

Fan coils [MWh/year] 10,5 21,0 21,0

TOTAL [MWh/year] 203,4 233,7 233,7

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7.7.3 Result

Since the costs of this measure are neglected, the result is equal to the saving through reduced cooling demand in computer labs.

Table 42: The economic calculations of the proposal in terms of saving, payback period and LCC.

Saving [MWh/year] Payback period [year] LCC

Scenario 1 203,4 - 1 250 000

Scenario 2 233,7 - 975 000

Scenario 3 233,7 - 975 000

7.7.4 Discussion

The location of the cooled areas is also essential for projecting the cooling and heating loads in buildings. This proposal has a theoretical value to show a different method that could be implemented for energy efficiency. However, this suggested proposal includes several complexities considering the potential implementation since computer labs have a large layout that require large areas. In addition, removing these labs can lead to a specific cooling requirement that was not considered in this study. Another drawback of this situation is that the heating requirements may also increase slightly, which indicates that a more detailed and advanced simulation need to be identify the best possible orientation and location with respect to energy efficiency.

This proposal has a significantly large potential to reduce the cooling demand compared to the current level. However, there are currently no other large areas that can accommodate number computers and occupants than computer rooms. Another consideration that was not pointed out and neglected here is the security and other technical specifications that is of high interest for the operations. This method can be complicated with the existing building configuration and would require major arrangements in the construction that could lead to high investments. It should be stated that this is a theoretic proposal that could have great potential and saving for future configuration and application of the computer rooms.

7.8 Power saving states in personal computers As it is mentioned in Chapter 7.1, the standard power saving option in the majority of the investigated computers as personal computers in the offices does not apply ant power saving states. During observation it was found that a high number of personal computers used in offices were running during nights and weekends. The most common arguments from employees are the long starting time and experienced stress when they need to wait for the computer to start. Another argument is the desire to be able to continue working with the same documents and programs they were last working with.

There are a number of power settings available in the computers that could solve these problems as they contribute to power reduction during nights and weekends. One alternative is to put the computers to hibernate state after a certain time of inactivity. Applying the “hibernate” power saving state has the ability to preserve all the active sessions in computer at the end of a working day. When

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the computer is restarted, all the programs and edited documents reopen at the same session they were left.

To base the assumptions on the real situation, an energy survey was performed to analyze the routines regarding computers and power saving options in D building. The following assumptions is made based on the acquired information, interviews and observations:

• The number of employees in D building is 450. • 15 % of the employees take their laptops home for nights and weekends. • 10 % of the employees turn off their computers after a workday. • 20 % of employees use “turn off display” option after a certain time of inactivity. • 5 % of the employees put their computers in sleep mode after a workday. • The working days are approximately 220 days per year.

Measurements have been conducted on several computers and screens of different type, age and activity level to estimate the average energy usage when the computers are in different power setting mode. The result and corresponding values are shown in APPENDIX 5.

7.8.1 Cost

Since the power-setting mode already exists in most of the personal computers, this proposal is not expected to generate any cost for the facility.


According to the estimations on the average energy consumption of the personal computers 73,7 % of power demand emerge between 16:00 -08:00 and during weekends. A direct effect of this energy measure would be the reduced energy waste during unoccupied hours in the building. The summarized saving of this proposal is presented in the Table 43. Since screens continue to consume power in hibernate state, disconnecting the screens during nights and weekends could lead to additional power saving.

Table 43: The energy consumption by using hibernate power setting and the savings. Calculations on LCC are also presented to summarize the total cost of the life cycle of the new proposals.

Power saving Occupied hours

[MWh/year]

Unoccupied hours

[MWh/year]

TOTAL Energy consumption [MWh/year]

SAVING [SEK/year]

LCC [SEK]

Current consumption

116,4 325, 4 441,8 - 3 590 000

Hibernate 116,4 140,5 256,9 184 900 2 090 000

Hibernate & disconnect screens

116,4 62,9 179,3 262 500 1 460 000

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7.8.3 Result

The revenue of this proposal is equal to the saving potentials, which is calculated to be 185 000 SEK/year for hibernate option and 262 500 SEK/ year for hibernating together with disconnecting the screens.

7.8.4 Discussion

Available technology and setting options in the existing computers allows the implementation of these types of energy measures. In addition, it could be relatively simple for the management to program such a power setting that could be a default setting for all available computers in the building. This proposal could have a positive side effect on the decreased heat load and reduced cooling demand in the computer labs. The measure partly relies on the expectation of a perfect behavioral regarding the applying power settings in personal computers. In this manner the outcomes of such a measure can be lower than expected.

7.9 Improving the lighting system in server rooms Today, the lighting in server rooms are always switched on or rarely switched off. The regular argument of having the lights on is the importance of being able to immediately see any possible failures when an employee enter these rooms. However, for fire protection and other safety factors, lighting in server rooms should be turned off in order to mitigate the fire risk. According to Thomas Persson, fire safety expert at Saab, electricity is one the most common risk factor to potential fires in buildings.

Energy saving can be achieved by eliminating inefficient electricity usage by switched off the lights in server rooms when they are unoccupied. Installing occupancy sensors could help to reduce the energy required to lighting systems.

The estimation on the average power consumption is based on gathered information on the power draw and the number of lamps used in server rooms. The characteristics and the number of these lamps in each server room and the estimated average power draw are summarized in Table 44.

Table 44: The power draw and number of bulbs in three server rooms.

Power [W] Number of bulbs

Power [W] Number of bulbs

Total power [W]

Room 1 58 10 14 2 608

Room 2 35 6 14 2 208

Room 3 35 6 14 2 208

Average power draw [W]

341

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7.9.1 Cost

The price of a simple occupancy sensor is assumed to be 300 SEK. Installation of one sensor in each server room will require a total of 11 sensors, which assumed to result in accost of 3 300 SEK. The expected investment costs are shown in Table 45.

Table 45: The expected costs for occupancy sensors and diverse installation cost.

Price Number Cost [SEK]

Sensors 300 11 3 300

Installation cost 600 SEK/hour 20h 12 000

TOTAL 15 300


The total working time in each server room is assumed to be around 4 h per day. If the lights could be turned off during the rest of the time, the amount of energy saved result in values presented in Table 46. Table 46: Comparison of the current and the new energy consumption by installing occupancy sensors in server rooms.

Energy saving [MWh/year]

Current energy consumption 32,9

New energy consumption 3,9

Saving 29

7.9.3 Result

Installation of new occupancy sensors will generate an annual saving of 29 000 SEK/year, which gives a payback period of approximately 6 months. The sensors should be replaced in 5 years, which is taken into consideration in economic analysis. The summarized costs, saving and payback time for this suggested energy measure are shown in TABLE 47.

Table 47: The estimated investment costs, LCC, saving and payback time by installing occupancy sensors in server rooms.

Investments [SEK] Saving [SEK/year] Payback [year] LCC [SEK]

15 300 29 000 0,53 73 400

7.9.4 Discussion

Reducing power draw to the lamps could decrease the additional heat loads generated from unnecessary usage of light. This measure will not affect the operations in server rooms. The important value of this proposal is the potential saving that would otherwise directly be added to generate costs. However, in larger server rooms, with a longer distance between servers and sensors, additional occupancy sensors would be necessary to install.

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8 Discussion The findings of this research can be seen as initial steps to make the energy system within the system development environments and related equipment at Saab facility more energy efficient. Some of the suggested energy efficiency measures showed a significant opportunity for reducing the use and thereby a reduction on the annual running costs in the building. A number of aspects have been studied in this project that have a considerable potential to be improved further. However, each of the energy measures is strongly dependent on a number of assumptions, technical characteristics, operational limitations and required capital investments.

One of the most important results found in this study is that the energy efficiency measures are strongly related to usage patterns and indoor thermal climate conditions. From this perspective, continuous investment in new technology and automation of energy system components can also be considered as secondary step for energy optimization. An example to this situation is described in chapter 7.1, where using the power settings in computers and screens in computer labs shows one of the most profitable energy measures. Increased awareness and participation of users might be an initial step to achieve the most optimal energy consumption in the building.

Observations and measurements show that the computer labs usually have a higher heat load compared to regular offices due to the high number of computers and monitors that are turned on during the day. However, since the computer labs are occupied areas, they should not have as high air flow rate as in the server rooms. For this reason the regulation and control of the thermal conditions in the computer rooms must be carefully adapted to the specific requirements of the occupants and electronic devices. For this reason there are number of aspects that should be considered before installing a cooling systems and cooling components in this environments. Another important factor that is missing in the existing computer labs is adequate heat rejection components, such exhaust air ducts/channels, to effectively remove the heat load from these rooms.

One of the most crucial factors that affect the distribution of cooling in computer labs is the current layout of fan coils. Having all the fan coils and ventilation openings placed in line, provides a heterogeneous distribution of cooling around these environments. Due to the fact of technological developments and increased usage of computer activities in the future, these rooms and their thermal conditions should be more carefully designed. In addition to the inefficient cooling from fan coils, the existing cooling units in the computer rooms are regularly shut down or blocked by the personnel. A common argument for this behavior from employees is to avoid high airflow rate that creates uncomfortable thermal climate. A general unawareness of the function of cooling units is also an issue. Therefore, the cooling components should be integrated with respect to thermal standards that provide satisfying conditions for the occupants and regulated automatically to achieve optimal conditions without limiting factors.

Human behavior plays a central role in the development of efficiency measures in modern office buildings. One of the main assumptions in the proposed solutions for energy usage optimization is that all of the occupants have an ideal behavior and act reasonable and responsible. Ideal behavior in this context refer to the optimal usage of electrical equipment which in turn improves the performance of the cooling system and indoor thermal conditions. However, since it is not always possible to control and predict the human factors energy efficiency usually focuses on the improvements of the existing

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energy systems. The major driving factor here is that the users often overweight factors such as comfort and the technological expectations than reducing the waste of energy. For this reason, the estimated level of energy efficiency and saving are not always achievable in reality. Therefore, the controlling options of power settings in screen and computers should be automated in order to maximize the energy saving. The same approach should be utilized for the cooling components, where cooling is automatically managed through cooling units and fan coils.

Considering the amount of cooling needed in the system development environments, it is important to secure an independent power generation. The investigated areas are relatively sensitive to temperature changes and it would be more suitable to have a backup cooling system for this electrical equipment. It is crucial to secure a continuation of business operation for the company. To avoid electricity supply problems, for example in case of potential failures in the energy system or in case of power cut, backup generators and cooling systems should be incorporated in the computer rooms.

Outcomes of the suggested energy measures showed that any implementation of energy measure in the studied environments would cause side effects, which will have significant impacts on the thermal condition in the adjacent offices. An example of this situation is reducing the supply air temperature in the AHU, which could result in a major effect on the entire building. As mentioned before, not all the computer labs have the same need of cooling, which means that solutions should be focused in the area with the specific problem. By doing so, it is possible to avoid undesired problems in other spaces of the building. Having this issue in mind, separating system development environments from offices should be highly prioritized before any implementation of energy measures.

An important thing to emphasize is that energy is more often an abstract term that does not have the same importance as the functionality of a computer. A general opinion regarding energy among interviewed employees was that the energy prices compared to the value of operations and generated work is low. For this reason energy reduction is not a primarily subject that should be taken into consideration. In general, energy prices can be seen relatively low in Sweden. In light of the development rate in rest of the world and the increasing demand on energy and dependence on technology, the electricity prices should not be reassumed to stay as low as it is today.

During the energy survey a number of operational errors were found. Measurements on the ventilation in the computer labs showed that the airflow rate in some of the distribution channels showed high deviations compared to the projected levels. This resulted in an unbalanced distribution of ambient air, which is crucial for removing warm indoor air more efficiently. Also, these rooms have a constant airflow rate and are usually over ventilated. To solve this problem, the airflow rate should instead be regulated with respect to occupancy in the computer rooms to optimize the energy consumption.

A relatively low electricity price may lead to less efficient use of energy, due to redundant access to energy in the modern societies. A significant amount of energy is wasted during the energy production, distribution and transmission chain, which can be compared to the amount of energy that has to be sacrificed for usage electricity in the electronic devices. Exploitation of Earth´s the limited natural resources such as petroleum, natural gas, nuclear and coal for energy production generate considerable impact on the environment and footprint. With accelerating number of technical applications that are highly depended on electricity in modern societies, an alternative way of thinking for energy utilization in buildings will be essential. In this concept, it is crucial to create awareness of

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the importance of unnecessary energy usage and associated environmental consequences to ensure a sustainable future and resilient society for the future generation.

8.2 Sensitivity analysis Several simplifications and assumption were made to be able to calculate the potential saving and costs of the energy measures and the energy demand. A sensitivity analysis is done in order to investigate the input parameters that have the most significant impact on the resulted factors.

8.1.1 Cooling demand in computer labs

One of the important assumptions in this study is that the cooling demand in the computer labs is climate independent. Computer labs are surrounded by a number of offices that acquire additional heat loads through fenestrations, which could indirectly contribute to increase cooling demand through increased room temperature. If the cooling in these environments changes by the same linear relation as it described in Chapter 6.3 in Figure 13, the new necessary refrigeration power would be fallowing the pattern, presented in Figure 20.

Figure 20: Impact on the refrigeration power in relation to the ambient temperature in computer labs.

In Figure 20 shows that the necessary cooling in computer labs changes according to changed ambient temperature. This means that as long as the computer labs are not isolated and strongly affected by the indoor climate changes in the offices, the climate dependent cooling requirements in computer labs has to be carefully considered.

With the new requirements, the total cooling demand in D building would increase, especially for the cooling system components such as chillers and pumps. Based on the climate dependent cooling conditions, the new energy consumption share for system development environments, chillers and pumps is presented in Figure 21. The result shows that considering the cooling demand in relation to ambient temperature, the yearly electricity cost for chillers and pump would increase by 133,4 MWh. By this adjustment, the total energy consumption share in the system development environments would end up at 67 % of the energy usage in the D building.

0 10 20 30 40 50 60 70 80 90

Ref

riger

atio

n ef

fect

[kW

]

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Figure 21: Sensitivity analyses on the cooling demand with changed ambient temperature compared to climate independent cooling. The energy consumption is shown for the yearly electricity consumption for chillers, pumps and the total energy demand in the system development environments.

8.1.2 Volumetric flow rate

Pumps in the cooling distribution system are assumed to have constant efficiency. T efficiency and power input of a pump is directly related to the volumetric flow rate of chilled water. Different operating points of a pump can lead to lowered efficiency or power requirements, which is neglected in the estimation of the power demand in most of the energy efficiency measures. In this regard changing the flow rate according to the demand will not directly result in the estimated power consumption.

8.1.3 Cooling units

One parameter that has a significant impact on the outcomes is the number of cooling units operating in the computer labs. Since these assumptions are based on the observations acquired in small number computer labs, the number of operating cooling units may be higher than the assumed value. In addition, the operation hours and usage patterns of these cooling units are highly uncertain due to manual control. Since cooling units generally require high power supply and large amount of chilled water, the findings of this study may not give an exact result.

8.1.4 Default power saving state

Another assumption that could have an impact on the savings generated by the potential implementation of energy measures is the default power saving states in personal computers. Observation on computer usage would have been more accurate if more interviews with employees were possible. In this case, it is probable that the assumptions of diverse power saving states in personal computers do not represent the real situation in D building.

0 500 1000 1500 2000 2500 3000

Chillers [MWh/year]

Pumps [MWh/year]

Total energy demand in the system development environmnets [MWh/year]

Climate dependent [MWh/year] Climate independent [MWh/year]

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9 Conclusions This thesis aimed to investigate the existing energy system and related components within the system development environments and to find suitable energy measure in order to reduce the energy consumption. The conducted energy survey within the defined system boundaries showed that cooling is the biggest energy consumer, which use 30 % of the total energy consumption in D building. One of the conclusions that can be drawn here is that the high amount of computers that are active during nights is one of the reasons for the high cooling demand. This situation is highly dependent on the current technical system requirements and human behavior regarding prevailing usage patterns.

The quantitative result of the proposals and analysis have revealed that the most profitable and technically possible solution to implement is related to the eliminating unnecessary usage of computers, screens and monitors during nights and weekends. It is important to emphasize that energy efficiency measures have strong correlation between user behavior and proper technical equipment to ensure satisfying thermal conditions in the system environments. Relaying only on the technical solutions for cooling demand and increasing the number of used electronic equipment without reducing the power used by this equipment during unoccupied hours will result in continuous energy consumption and unbalanced thermal conditions.

The current layout and placement of computer labs does not allow an effective cooling. This is due to the continuous heat loads from manually controlled heating and cooling regulations in offices located around computer labs. Even if the existing building construction does not have the capacity to resettle the computer lab in other spaces, the location of these environments should be a crucial factor that should be considered for the future implementations. Each of the suggested energy measures in these rooms has a limitation of not giving the expected result. This is due to the continuous energy transfer between offices and computer rooms. To achieve effective cooling, these environments should also be isolated or removed to eliminate the thermal heat loads gained from offices located around the computer rooms.

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10 Future studies One of crucial aspects that should be pointed out as a result in this study is that from a cooling and thermal comfort perspective the computer labs require a more sophisticated and specific cooling than the existing office and server rooms. Combining the high heat load from computers and other electronic equipment and the occupancy of employees lead to a increased the complexity level of the cooling system that has to provide different demand during different time spans. For this reason, a deeper analysis of the various cooling method should be investigated to decide an optimal performance and interaction that can increase the refrigeration power and thermal climate conditions in computer rooms.

An interesting parameter that could be worth to investigate in the future studies is to analyze the most applicable cooling system and type of cooling components for a typical structure of the existing computer labs. Considerations should have a focus on placement, capacity and orientation of cooling units that need to be installed in computer labs. The heat load development from equipment, people as well as the offices around these environments should be also included in this investigation. The use of energy simulation software´s can contribute to identify the predominant fluid dynamics around these environments and achievements from these simulation could be implemented in the future applications. This may provide the most optimal options to maintain the thermal conditions for occupants and the most energy efficient cooling usage for electrical equipment, computers and monitors.

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Appendix 1 The measured temperature of the chilled water in the chilled water system in D building is shown in Table 48. Table 48: The volume flow and corresponding the supplied refrigeration power in the three main cooling distribution loops KB01, KB02, KB03 and KB04. The temperature of the inlet and return chilled water in each loop is measured on the outer walls of the distribution pipes.

Cooling distribution loops

Volume flow [m^3/h]

T in [℃] Tout [℃] Total refrigeration capacity [kW]

KB01 99,7 9,8 7,2 296,623

KB02 46 14,3 12,4 101,967

KB03 63 - - 131,950

KB04 87 17 15,7 131,950

Total volume flow rate and refrigeration power that is required for components defined in the system boundaries is given in Table 49. Table 49: The volume flow rate of chilled water and required refrigeration power to different cooled areas in the system.

KB01 [m^3/h]

KB02

[m^3/h]

KB03

[m^3/h]

KB04

[m^3/h]

Total refrigeration capacity [kW]

Computer labs [Fan coils] [m^3/h]

- - - 17,206 26,096

Computer labs [Cooling units] [m^3/h]

8,208 - - - 16,279

Server rooms [Active cooling units] [m^3/h]

- - - 13,310 20,187

Server rooms [Passive cooling units] [m^3/h]

- 17,640 - - 53,508

Ventilation 29,077

TOTAL refrigerant effect required from KB01 [kW]

162,446

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Appendix 2 Measurements on the power supply to the chiller, VK03, are given in Table 50. Table 50: The momentarily measured power supply to the chiller VKA02.

Date Time Power input [kW]

2017-03-13 13:00 37,008

2017-03-14 16:00 39,636

2017-03-15 09:00 42,566

2017-03-15 15:00 39,240

2017-03-16 09:00 38,304

2017-03-16 16:00 37,872

AVERAGE 39,104

The following relations are used to calculate the coefficient of performance in the chillers:

The average power supply to VKA2 = 39,104 kW

The total power demand to the chillers (VKA03+VKA02) =70,837 kW + 39,104 = 109, 94kW

The coefficient of performance in the chillers: 𝐶𝑂𝑃! = !!!= !"#,! !"

!"#,!"= 2,698

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Appendix 3 Measured power draw to the computer and screens in different power options are shown in Table 51 and Table 52.

Table 51: The measured power supplied to the screens in different power options.

Model Size Idle [W] Screen off [W] Sleep mode [W]

Unplugged [W]

Screen

Dell Small 45,54 9,32 9,32 0

Miscellaneous Small 30,02 4,14 4,14 0

Philips Medium 45,55 4,17 4,17 0

Dell Medium 55,89 10,35 10,35 0

HP Medium 66,49 9,32 9,32 0

Samsung Medium 71,41 0 0 0

Dell Medium 93,15 3,105 3,105 0

HP Large 93,15 19,67 19,67 0

Dell Large 90,04 9,315 9,315

Average power draw [kW]

62,65 8,58 8,58 0

Table 52: Power draw in different model of computers by using different power saving options.

Model Idle Sleep mode

Computer

HP 100,91 25

Miscellaneous 121,84 -

Miscellaneous 82,8 -

Average power draw [kW] 101,85

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Appendix 4 Following parameters have been used as input values in the simulation with software “Swegon Esbo” Table 53: Parameters that are used in simulation with "Swegon Esbo".

Parameters Values

Height of the wall 2,8 m

Width of the wall 5,8 m

Length of the wall 16,7 m

Height of the window 1,6 m

Length of the windows 11, 11

Glazing of the windows Double clear air- 2 panes-

Heat transfer coefficient of windows 2,88 W/m2*K

Number of occupants 10 person

Schedule for occupancy 9:00-17:00 during weekdays

Light 865 W

Equipment 4,82 W

Indoor Climate Standards

Heating set point 19 C

Cooling set point 24 C

Air quality control CO2 (<1000 ppm)

Supply air temperature 19,5 C

Supply air flow 283 l/s

Type of shading Exterior shading

COP of the cooling system 2,7

The results of simulation with the given input parameters are shown in Table 54. Table 54: Cooling demand depending on different orientation and location of the computer labs simulated with help of “Swegon Esbo Light”. .

Orientation Building inner walls

[MWh/year]

One exterior wall (with window) [MWh/year]

Two exterior walls (with window) [MWh/year]

North 87,708 46,164 44,376

South 87,708 43,032 40,836

East 87,708 46,500 45,252

West 87,708 45,864 44,076

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Appendix 5 Table 55 shows the average power consumption level on the measured screens and computer using power saving features available in most of the computers at the facility. Table 55: Impact on the power supply to computers and screen using different power saving states.

Power saving state Screen [W] 1 laptop + 2 Screen [W]

Idle 51,75 146,97

Turn off display 12,42 72,45

Hibernate 12,42 26,91

Unplug screens 0 6,70

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