ND Central Plant AC GSBN Key Inputs v1.1

Version: 1.1 First created: 22/03/2009 Updated: 15/06/2010 http://efficient-products.defra.gov.uk Last reviewed: 15/06/2010 1 of 18 0845 600 8951

BNCAC01: Central Air Conditioning Plant, Government Standards Evidence Base 2009: Key Inputs

Version 1.1

This Briefing Note and referenced information is a public consultation document and will be used to inform Government decisions. The information and analysis forms part of the Evidence Base created by Defra’s Market Transformation Programme.

1 Introduction

• The aim of this Briefing Note is to provide details and reference sources of the underlying data in central plant air conditioning unit models, along with the key assumptions used in these models. There are three main sections to this Briefing Note, corresponding to the main variables of the MTP modelling approach:

o Ownership & stock o Sales o Usage & lifespan

• Each section also includes an indication of the overall confidence in the dataset, to provide a sense of the robustness of the model.

1.1 Product Definitions

• Air conditioning systems can be divided into;

o small, where unit and split air conditioners dominate, o medium, where the market is divided between multi-split systems and air-cooled

systems, and o large, where the cooling is mostly delivered by air that is cooled centrally (as in a

variable air volume or VAV system) or in a combined system with fresh air-cooled centrally, and further cooling provided within the room spaces by a large number of Fan Coil Units (FCUs).


• This Briefing Note focuses on large systems where central plant air conditioning units are defined as systems, or components of systems, that deliver heating, cooling and ventilation services to a building from a central unit and accompanying distribution system. However, this briefing note is only concerned with the cooling demand provided by Central Plant Air Conditioning.

Chillers

• Chillers are an integral component of air-conditioning and comfort cooling systems. There are three principle types:

Absorption chillers

• Absorption chillers use a heat source to produce chilled water. The cooling effect occurs when refrigerant evaporates thereby removing heat. The resulting gas is regenerated into liquid by applied heat, completing the cycle. These systems use either lithium bromide/water or ammonia/water solutions; water is the refrigerant in the former and ammonia in the latter.

• Absorption chillers are an alternative to regular compressor chillers where: electricity is unreliable, costly or unavailable; noise from the compressor is problematic; or excess or waste heat can be cost-effectively utilised (e.g. from CHP plant or industrial processes).

• Absorption chillers are generally classified as ‘direct-fired’ or ‘indirect-fired’. In direct-fired units, the heat source can be gas or some other fuel that is burned in the unit. As a rule, these devices produce cooling with a higher energy-related carbon output than a mains-driven electrical chiller. Indirect-fired units use steam or some other transfer fluid that brings in heat from a separate source, such as a boiler or heat recovered from combined heat and power (CHP) or an industrial process. Hybrid systems are relatively common and combine absorption chillers with electric systems for load optimisation and flexibility.

• Capital cost is the primary constraint on the widespread adoption of absorption chiller systems, although as their most effective application is using waste heat in association with CHP systems, the market is also limited.

• As a result, of all chiller types purchased in 2007 only 2% were of the absorption variety. Absorption chillers are available in a wide range of sizes from 17kW to MW size. The largest market sector for absorption chillers is between 17.6-50 kW, representing 76% of all absorption chiller sales in 2007.

Air-cooled chillers

• Air-cooled chillers utilise air to cool heat rejection coils. Ambient air is fan-forced over the chiller’s condenser coil to expel heat into the atmosphere. Compared to water-


cooled chillers, air-cooled chillers are easier to locate and maintain; require more space, and do not require a dedicated water supply. They are, however, generally less energy efficient than water-cooled units.

• A range of commercial and industrial applications are available, sized from a few kW to a few MW. In 2007 21% of air-cooled chiller sales were sized 201 – 350 kW, 12% were less than 17.5 kW, and 5% were over 901 kW. Of all chillers purchased in 2007 88% were of the air-cooled variety.

Water-cooled chillers

• Water-cooled chillers are used where a high cooling demand exists, such as large commercial and industrial buildings. The improved cooling provided by this type of chiller results in higher system energy efficiency; therefore they will be considered when optimum efficiency is a priority. They can also be considered when a cooling tower is already in place, or where the space available is insufficient to accommodate an air-cooled chiller.

• The heat rejection water is distributed with a cooling tower by means of a fine spray or splash bars, to create a greater surface area. Ambient air travels through the cooling tower either by natural convection, or forced by a fan when required, and heat is transferred from the water to the air. The resulting exhaust air can be saturated with water vapour resulting in a plume of visible discharge air, if not carefully controlled.

• 10% of all chillers purchased in 2007 were of the water-cooled variety. The largest market sector was between 100kW to 350kW, comprising 43% of total water-cooled chiller sales in 2007.

Air Handling Units ● Air handling units (AHUs) manage the distribution of air within a building or space.

This is achieved through a combination of exhaust and supply fans, air filters, sound attenuators and heating/cooling coils. The unit is typically connected to ductwork running the span of the space to be conditioned. Cooling and heating coils are fed independently either from a chiller or other refrigeration unit and a boiler. AHUs may also incorporate heat recovery, either through re-circulating exhaust air (known as direct heat recovery) or by extracting only heat from the exhaust stream via a heat exchanger.

● Almost all of the energy consumption in an AHU is attributable to the fans, which

can be fitted with variable speed drives to regulate their frequency of operation enabling them to ‘throttle down’ when large-volume ventilation is not required.

• In this evaluation, the AHU market has been simplified to model only the fan and electric drive system. This is because the cooling/heating elements will derive their


thermal energy from outside of the AHU and will be accounted for in the respective models for chillers or other cooling systems and boilers. Also, other electrical demands inside the AHU are very small compared to that required by the fan.

Schematic of an air handling unit (AHU)

Obtained from http://www.automatedbuildings.com/news/aug08/reviews/080725081501computrol.htm

Fan Coil Units

• A fan coil unit (FCU) is a simple device consisting of a cooling and/or heating coil and fan. It is part of an HVAC system found in residential, commercial, and industrial buildings. Typically a fan coil unit is used to control the temperature in the space where it is installed, or serve multiple spaces. It is controlled either by a manual on/off switch, a thermostat or by a building management system.

• In this evaluation, the FCU market has been simplified to model only the fan and electric drive system. This is because the cooling/heating elements will derive their thermal energy from outside of the FCU and will be accounted for in their respective models. Also, other electrical demands inside the FCU are very small compared to that required by the fan.


2 Ownership & stock

2.1 Summary

Figure 1 Central Air Conditioning Plant stock

Table 1 Summary figures – stock (model output)

Stock 2008 - 2030

Year

TOTAL Absorption

Chiller

Air-cooled Chiller

Water cooled chillers AHU FCUs

2010 1,363,440 917 32,133 5,669 224,445 1,100,276

2020 1,296,688 1,389 39,299 7,364 247,209 1,001,427

2030 1,461,116 2,448 46,217 10,593 235,958 1,165,900

2.2 Data sources – stock

No direct data available – derived from sales data – see below.


2.3 Methodology & key assumptions - stock

2.3.1 Historic data

Table 2 Interpolation & background calculations – stock data

Year Product type

Methodology & assumptions

All The modelling adopted is sales-based. It calculates stock automatically using a sales projection, the product lifetime and a sales churn calculation which accounts for products purchased in previous years gradually being taken out of commission at the end of their lifetime. Real stock data are put in as a check only, to help evaluate the output sales from the model. This data series is usually incomplete.

1981 - 2001

All chillers, AHUs

Stock data obtained from sales data of MTP model 2008.

2002 All Stock data calculated in MTP model from earliest obtainable recorded sales data from BSRIA (2007) report.

2003 - 2008

All Stock data calculated in MTP model from recorded sales data from BSRIA (2009) report.

1960 - 1985

FCUs Assumption that in year of product’s introduction to the market, 460 units were sold. Thereafter, sales increased linearly by 1,490 units each year. Consistent with expert opinion and anecdotal evidence, although precise rate of growth may vary.

1986 - 2001

FCUs Stock data obtained from sales data of MTP model 2008.

2.3.2 Future analysis

Table 3 Extrapolation & background calculations – stock data

Year Product type


All The modelling adopted is sales-based. It calculates stock automatically using a sales projection, the product lifetime and a sales churn calculation which accounts for products purchased in previous years gradually leaving stock. For sales assumptions, see Section 3.

2.4 Data issues – stock

Table 4 Data issues – stock

Issue/risk Approach taken/rationale All stock estimates have been derived from sales data.

Obtained best available sales and lifetime data from approved industry research body BSRIA. Correlation with any available stock data may be required.

Projected absorption & air-cooled chiller and AHU stock data may be inaccurate.

Stock data obtained from projected sales data, based on latest extrapolation from BSRIA (out to 2012) and then on expected market factors.

2.5 Confidence level

• The confidence level indicated below is due to limited sales data (5 years).


Figure 2 Confidence indicator for stock data

Da

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LOW

LOW HIGH Source integrity / robustness of data

3 Sales

3.1 Summary

Absorption chillers

• In the medium to long-term (beyond 2012), the key factors envisaged to affect absorption chiller sales include technological improvements and changing climatic conditions (e.g. excessively warm summers and higher average temperatures).

Air-cooled chillers

• BSRIA reports that currently, air-cooled chillers account for 88% of the chiller market, and further expansion of this market share over the years to 2030 is unlikely. Current, recession-related stagnation is expected to be followed by modest growth related to the 2012 Olympics. Although overall sales may grow in the long term due to new construction, lack of alternative technologies for large chillers, and an additional demand for cooling, the rate of growth may be 1% pa, as is modelled from 2017.

Water cooled chillers

• For water-cooled chillers, BSRIA notes that 100-300kW units dominate the market and that there is a general trend of growth in this product sector due to perceived energy efficiency. Continued growth is expected from 2008 – 2014. From 2014 - 2022 the sales are modelled to fluctuate as the technology seeks to assert itself as an alternative to small air-cooled chillers, given the trend away from high Specific Fan Powers (SFPs) and large volumes of air for cooling. From 2022, sales are modelled to grow at a rate of 7% pa, at a time when air-cooled units that were installed during the economic recovery and the Olympics reach the end of their economically serviceable lives and water-cooled systems are installed as more efficient alternatives.


Air handling units

• Sales are projected to decrease in line with the overall trend seen from recorded sales data. However, a temporary surge in sales is expected from 2015 to 2016 which demonstrates a degree of volatility in the market seen between 1990 and 1998. Thereafter, the AHU market trend is downward as competing technologies and natural ventilation strategies reduce market demand.

Fan Coil Units

• FCUs are present in medium sized systems and a large proportion of larger ones. As a consequence sales are very sensitive to the construction of air-conditioned buildings, and construction of a few large buildings can cause a significant and temporary increase in sales. Thus the market is very volatile.

• This volatility is reflected in the measured sales data from BSRIA. The projections before and after the period reported by BSRIA do not show such volatility due to smoothing. A gradual increase in market demand over the years leading up to the late 1990s is followed by higher sales as a result of a surge in construction of large, air conditioned buildings. After volatile demand early this century, growth in sales are expected to resume, and projections are based on a steadier rate of growth through to 2030.


Figure 3 Summary figures – sales

Table 5 Summary figures –sales

Sales

Year

TOTAL Absorption

chillers Air-cooled

chillers

Water cooled chillers AHUs FCUs

2010 70,330 75 1,981 337 12,083 55,854

2020 87,291 118 2,947 502 13,309 70,415

2030 105,960 222 3,255 904 11,442 90,137


3.2 Data sources - sales

Table 6 Sales data sources

Year Product type

Reference

Reference date

Author Justification Confidence in sources (High/Low)

1980 - 2001

All chillers, AHUs

Expert assumption

October 2008

MTP Technical Expert

Only data source available

Low

2002 All chillers BSRIA Report 19653/6A – Chillers (UK) Sept 2007

February 2009

BSRIA Recorded sales data from this leading trade body used to compile stock data in MTP model

High

2003 – 2008

All chillers BSRIA Report 50571/6A Ed2 – Chillers (UK) Jan 2009

February 2009

BSRIA

Recorded sales data from this leading trade body used to compile stock data in MTP model

High

2009 - 2012

All chillers BSRIA Report 50571/6A Ed2 – Chillers (UK) Jan 2009

February 2009

BSRIA

Sales data projected by this leading trade body used to compile stock data in MTP model

High

2013 – 2030

All chillers Expert assumption

February 2009


Expert judgment of sales data used to compile stock data in MTP model

Low

1960 – 1985

FCUs Expert assumption

March 2009 MTP Technical Expert


Low

1986 - 2001

FCUs Expert assumption

October 2008

BSRIA


Low

1960 - 1979

AHUs Expert assumption

March 2009 MTP Technical Expert


Low


Year Product type

Reference

Reference date

Author Justification Confidence in sources (High/Low)

2002 AHUs BSRIA Report 19653/6B– Airside Products (UK) Nov 2007

March 2009 BSRIA


High

2002 FCUs BSRIA Report 19653/6B – Airside Products (UK) Sept 2007

February 2009

BSRIA


High

2003 - 2008

AHUs, FCUs BSRIA Report 50571/6B Ed2 – Airside Products (UK) Jan 2009

February 2009

BSRIA


High

2009-2012

AHUs, FCUs BSRIA Report 50571/6B Ed2 – Airside Products (UK) Jan 2009

February 2009

BSRIA

Sales data projected by this leading trade body used to compile stock data in MTP model

High

2013 – 2030

AHUs, FCUs Expert assumption

February 2009


Expert judgment of sales data used to compile stock data in MTP model

Low


3.3 Methodology & key assumptions – sales

3.3.1 Historic data

Table 7 Interpolation & background calculations – sales data

Year Product type


1980 - 2001

All chillers Sales data obtained from 2008 MTP model.

2002 All Earliest obtainable recorded sales data from BSRIA (2007) report.

2003 – 2008

All Recorded sales data from BSRIA (2009) report.

1960 – 1979

AHUs Expert assumption on linear increase in sales of 370 units per year from starting value of 100 units sold in 1960.

1980 - 2001

AHUs Sales data obtained from 2008 MTP model.

1960 - 1985

FCUs Assumption that in year of product’s introduction to the market, 460 units were sold. Thereafter, sales increased uniformly by 1,490 units each year. Consistent with expert opinion and anecdotal evidence, although precise rate of growth may vary.

1986 - 2001

FCUs Sales data obtained from 2008 MTP model.


Table 8 extrapolation & background calculations – sales data

Year Product type


2009-2012

All Projection of sales made in BSRIA (2009) report.

2013-2015

Absorption chillers

2% pa growth rate due to weathering of economic downturn until 2012 by the product market and reflecting an expanding construction market (especially for development-sized projects) due to Olympics legacy projects.

2016-2019

Absorption chillers

5% pa growth in the market due to increased application of CHP systems, which are proving popular for large-scale public sector projects such as hospitals and new school buildings under the Building Schools for the Future (BSF) Programme.

2020-2023

Absorption chillers

6% pa growth to reflect increased popularity of the product in displacing air-cooled chillers in some applications, due to trend moving away from large volumes of air for cooling.

2023-2030

Absorption chillers

6.5% pa growth due to increased uptake by the market in light of applications using CHP systems and potentially solar absorption cooling towards the end of this time period. This is a conservative estimate, as BSRIA notes that a higher rate of uptake would only be achieved through Government incentives.

2013-2014

Air-cooled chillers

That sales will behave as described by the BSRIA (2009) report’s assertion that post-2012 will see recovery in the construction market and this market will be buoyed, in part, by new construction from Olympics legacy development. As such, a 4% growth rate is modelled to represent market recoil.

2015-2016

Air-cooled chillers

A 6% pa growth rate is assumed as a consequence of Olympic legacy development.


Year Product type


2017-2030

Air-cooled chillers

Conservative growth of 1% pa estimated due to stable market (albeit with a higher proportion of large-size chillers being sold).This is modelled to continue the general growth trend in the market seen since the product was introduced, but increased competition from water-cooled chillers is expected.

2013 Water cooled chillers

4% pa growth rate as a consequence of new construction instigated by development related to the Olympics legacy developments and the expected stability of the construction market by this time.

2014-2015


7% pa growth to reflect increased popularity of the product in displacing air-cooled chillers in some applications.

2016-2017


2% pa decline in market due to assumed volatility such as market prices etc. This is to reflect that water-cooled chiller products will initially struggle to displace the established market of air-cooled chiller equipment.

2018-2019


7% pa growth to reflect increased popularity of the product in displacing air-cooled chillers in some applications.

2020-2022


2% pa decline in market due to assumed volatility such as market prices etc. This is to reflect that water-cooled chiller products will initially struggle to displace the established market of air-cooled chiller products.

2023-2030


7% pa growth estimated as these units replace the air-cooled chillers installed during the (expected) 2012 construction period which reach the end of their serviceable lives.

2013 – 2014

AHUs Assumption that sales will behave as described by a 1% pa growth rate in sales after 2012. This is in line with recorded trends obtained from BSRIA (2009) report.

2015 – 2016

AHUs A short, sharp increase in sales resulting in 5% pa growth in the market is modelled as a response to a surge in replacement demand for units installed around 2000. As decentralised cooling and other technologies reach technological maturity in the market place, diversification into other technologies is not projected until uptake of other ventilation technologies is proven successful.

2017 - 2030

AHUs A steady decline in the market of 1.5% pa is modelled to reflect the replacement of the product by other technologies and natural ventilation strategies.

2013 - 2015

FCUs A general trend of 1% pa growth is assumed due to prevailing opinion in engineering industry that decentralised air conditioning constitutes good practice design. This is commensurate with improvements in the technology that have seen the trend to move away from AC units to DC (electronically commutated) units that are more efficient and require less maintenance.

2016 - 2030

FCUs A general trend of 2.5% pa growth is assumed due to prevailing opinion in engineering industry that decentralised air conditioning constitutes good practice design. This is commensurate with improvements in the technology that have seen the trend away from AC units to DC (electronically commutated) units that are more efficient and require less maintenance.

3.4 Data issues - sales

Table 9 Data issues – sales

Issue/risk Approach taken/rationale Small sample of chiller sales data. Best available sales data has been sourced from

leading trade research body BSRIA.


3.5 Confidence level

• Confidence level rationale based on sales data for only 5 years and related uncertainties.

Figure 4 Confidence indicator for sales data

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LOW

LOW HIGH Source integrity / robustness of data

Usage & lifespan

3.6 Summary

• Average usage hours have been assumed in the following table, reflecting the variety of uses within the air-conditioning market.

• Whilst the usage values described portray a reasonable picture of product usage, they may not accurately convey the patterns of usage associated with the following:

o Specific weather events such as an especially warm week in summer o A general trend towards a warmer climate, as outlined by UKCIP02 o Expected improvements in the building stock such as passive design and

the associated reduced cooling requirement o Unit cost of electricity o The effect of intelligent building systems to accurately control provision of

cooling to meet with demand. Table 10 – Usage hours per unit in Reference, Policy and BAT Scenarios

Usage (hours/year)

Year

Absorption chillers

Air-cooled chillers


AHUs FCUs

2010 5,000 1,000 2,500 3,120 3,120 2020 5,000 1,000 2,500 3,120 3,120

2030 5,000 1,000 2,500 3,120 3,120


Table 11 – Average lifespan of unit in Reference, Policy and BAT Scenarios

Lifespan (years)

Year

Absorption chillers

Air-cooled chillers


AHUs FCUs

2010 17.5 15.5 18.5 18.5 15.5

2020 17.5 15.5 18.5 18.5 15.5 2030 17.5 15.5 18.5 18.5 15.5

3.7 Data sources – usage & lifespan

Table 12 Usage data sources

Year Product type

Reference

Reference date

Author Justification

Confidence in sources (High/Low)

1980 - 2030

Absorption & Air-cooled chillers, AHUs, FCUs

Expert assumption

October 2008



Low

1980 - 2030


Expert assumption

April 2009 MTP Technical Expert


Low

Table 13 Lifespan data sources

Year Product type

Reference

Reference date

Author Justification

Confidence in sources (High/Low)

1980 - 2030

All Expert assumption

October 2008



Low


3.8 Methodology & key assumptions – usage & lifespan

• Data has been sourced according to the methodology and assumptions as shown in Table 16.

3.8.1 Historic data

Table 14 Interpolation & background calculations – usage & lifespan data

Year Methodology & assumptions Usage

1980 - 2008 Assumption that usage remained constant during this time, and will not be significantly affected by environmental factors or quality/quantity of UK building stock.

Lifespan

1980 - 2008 Assumption that products have a constant lifespan.


Table 15 Extrapolation & background calculations – usage & lifespan data

Year Methodology & assumptions Lifespan

2009 - 2030 Assumption that lifespan will not be significantly affected due to technological or policy effects.

Usage

2009 - 2030 Absorption chillers; Absorption chillers have higher capital costs than electric alternatives. Because of this, they are more likely to be used in applications requiring longer running hours. Thus 5,000 hours of annual usage estimated is higher than those assumed for conventional air and water cooled chillers.

Air-cooled chillers: Some chillers, especially the smaller ones, will operate for quite short periods, essentially for cooling at peak times only. Others will have much longer running hours, throughout the summer season or all year. This is represented by an average operating time of 1000 hours per year.

Water cooled chillers: Some water cooled chillers will operate for very short periods, essentially cooling at peak times only. Other chillers will have much longer running hours throughout the summer season or all year. However, water cooled chillers will tend to be installed in locations with higher cooling demands. 2,500 hours of annual usage is chosen to represent the overall average of this varied market.

Air Handling Units (AHUs): Annual usage of 3,120 hours is chosen to represent a typical year of cooling requirements across the AHU market. The figure represents 12 hours for 5 days a week, reflecting the typical applications of AHUs in commercial buildings where ventilation and air conditioning may be required throughout operational periods.

Fan Coil Units: Air conditioning systems using fan-coil units are mostly installed in office buildings. These systems operate for slightly extended office hours, which equates to approximately 2,000 – 2,500 hours per year. Some FCUs operate continuously. 3,120 usage hours per year represents a weighted average equivalent to operation at 60 hours/week.


3.9 Data issues – usage & lifespan

Table 16 Data issues – usage & lifespan

Issue/risk Approach taken/rationale Usage

No change (either historic or projected) in usage data suggests it is independent of quality of building stock and prevailing climate.

Maintaining constant usage allows the reference line to act as a suitable control case. An investigation into probable degree days and penetration of efficient building envelopes in the market would be required to improve this significantly

Value of usage hours of chillers may be inaccurate.

Hours of usage deemed to be a reasonable annual average in non-domestic buildings for chillers, in the absence of data to the contrary

Constant usage implies lack of technology diversification for particular cooling requirements.

Projected usage does not show market capture of absorption chillers by any other technology.

Lifespan

The lifespan of the product does not change over the entire period 1980-2030 (1960-2030 for AHUs) as would be expected through a better use of materials, etc.

A changing lifespan would skew the stock model, and therefore energy consumption considerably, either reducing the impact of energy efficiency or exaggerating them. A constant lifespan as a single frame of reference has been used in the absence of reliable data.

3.10 Confidence level – usage & lifespan

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LOW HIGH

Source integrity / robustness of data

Figure 5 Confidence indicator for usage & lifespan data

Related MTP information

• BNCAC02: Central Plant Air Conditioning Units Government Standards

Evidence Base 2009: Reference Scenario


Evidence Base 2009: Policy Scenario


Evidence Base 2009: Best Available Technology Scenario


• BNCAC KO01: Central Plant Air Conditioning Units Government Standards

Evidence Base 2009: Key Outputs

Changes from previous version

• This is the second publication.

Consultation and further information

Stakeholders are encouraged to review this document and provide suggestions that may improve the quality of information provided, email [email protected] quoting the document reference, or call the MTP enquiry line on +44 (0) 845 600 8951. For further information on related issues visit http://efficient-products.defra.gov.uk

ND Central Plant AC GSBN Key Inputs v1.1

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