1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of KES International.doi: 10.1016/j.egypro.2017.03.029

Energy Procedia 111 ( 2017 ) 277 – 286

ScienceDirect

8th International Conference on Sustainability in Energy and Buildings, SEB-16, 11-13 September 2016, Turin, ITALY

Exploring Energy Conservation in Office Buildings with Thermal Comfort Criterion towards Sustainable New Developments in Warm

and Humid Climate

Pradeep Kinia*, Naresh Kumar Gargb, Kiran Kamathc aFaculty of Architecture, Manipal University, Madhav Nagar, Manipal 576104, India

bSchool of Architecture and Design, Manipal University, Jaipur 303007, India cDepartment of Civil Engineering, Manipal University, Madhav Nagar, Manipal 576104, India

Abstract

India is experiencing rapid urbanization and there is tremendous growth in the building construction sector since the last decade. India has proposed 100 smart cities and the offices/commercial built space is expected to increase fourfold between 2015 and 2030. Building sector consumes 40% of the world’s energy and is the single leading contributor to anthropogenic climate change. The office buildings in the warm and humid region in India are mostly installed with air-conditioning to maintain indoor thermal comfort. This system consumes the most energy of all building services representing 55% of the total energy consumption in office buildings and has the largest potential in energy savings. As a case study, a six storey office building in Manipal in Coastal Karnataka, India is documented and simulated for indoor thermal comfort analysis. Various building envelope design strategies are examined in order to improve indoor temperatures and conserve energy towards sustainable new developments in warm and humid climate.

© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of [KES International.]. Keywords: Building Envelope; Warm and Humid Climate; Building Energy Simulation; Thermal Comfort; Natural Ventilation

* Corresponding author. Tel.: +91-9019695055

E-mail address: pradeep.kini@manipal.edu

Available online at www.sciencedirect.com

© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of KES International.

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1. Introduction

In recent years, facing the risk of climate change and depletion of fossil fuels, reduction in energy consumption is an environmental sustainability goal for many countries, including India. With a population of 1.1 billion people and one of the fastest-growing economies in the world, India is experiencing a rising demand for energy. According to International Energy Agency, India’s CO2 emissions are expected to nearly triple between 2015 and 2030 [1].

One driver for this increase in energy use and carbon generation is the growth in building stock expected over the coming decades. Based on forecasts of building construction, it is estimated that about 70% of the commercial floor space that will exist in India in 2030 is yet to be built [2]. According to India’s Central Electricity Authority the current energy installed capacity in the country is 160,000 MW and the projected energy load for 2030 is 800,000MW. India’s demand for commercial energy is surging and there is an urgent need by the building sector to adopt non-energy intensive systems with a low carbon foot print. Challenge before India is to plan and implement energy efficiency measures during the early stages of growth in the building sector, so research to reduce energy consumption in the building sector through passive design strategies without compromising human comfort is essential. There is tremendous amount of construction activity in the warm and humid region of coastal Karnataka and most of the office buildings are designed for space cooling using air conditioning systems. The Heating, Ventilation and Air-conditioning (HVAC) systems in office buildings contribute substantially to the energy consumption and there is now a pressing need to address cooling needs. The National Building Code of India (NBC) specifies two narrow ranges of indoor comfort temperatures (23-26°C) irrespective of the type of building or its climatic location [3]. NBC follow the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard-55 and designers overdesign HVAC as per Predicted Mean Vote (PMV) comfort model resulting in unnecessary wastage of energy. The recent trend in India is to design air-conditioned office buildings that often operate at 22.5 ± 1°C all year round to meet the stringent comfort specifications articulated in documents such as the International Standardization Organization’s comfort standard (ISO, 2005). Air-conditioning systems consumes the most energy of all building services, which comprises 55% of the total energy consumption in commercial buildings and has the largest potential in energy savings [2]. Recent studies have found that the comfort temperatures to the tune of 31.45°C with or without the use of fan were achieved in indoor environments, as against the stipulated standard comfort zone of (23-26°C) [4]. Providing a comfortable environment for occupants in office buildings should be a high priority without which the building will have decreased worker productivity. Thermal comfort is an effective criterion to integrate the various impacts of facade components on indoor thermal environment. An important factor that affects thermal comfort in buildings is the thermal performance of the building envelope and for this reason building design in warm humid climates needs to get more attention to building orientations, shading devices, material selections and window design [5, 6].

With the increase of air velocity the indoor temperature of thermal comfort can be increased [7, 8]. As the benefits of natural ventilation, including reducing operation costs, improving indoor air quality and providing satisfactory thermal comfort in certain climates are recognized, passive cooling of offices using natural ventilation has become an attractive option to design low energy buildings which are environmentally sustainable. There are many research studies related to the energy consumption due to the impacts of building facade components in sealed air conditioned buildings and mechanically ventilated buildings [9, 10]. Research related to building envelope designs towards energy savings and thermal comfort is deficient especially for office buildings in warm and humid climate. The research objectives are to use simulation tools to analyze the role of building envelope design and natural ventilation in achieving adaptive thermal comfort in office buildings in warm and humid climate.

2. Methodology

Several office buildings in the warm and humid region along the west coast of India were surveyed in 2012-13 to understand the generic architectural design principles, current construction practices adopted and energy consumption scenarios. The study reveals that the most of the office buildings surveyed were designed without any climatic considerations and mainly used reinforced cement concrete for roof slabs and concrete block for masonry walls with cement plastering. The indoor temperatures remains very high during the day because of heat gain through the building envelope and most of the office buildings use air conditioning systems due to occupant thermal discomfort. To

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accomplish the research objectives, a six storey office building in Manipal in coastal Karnataka, India is taken for detailed analysis and demonstration. The Bureau of Indian Standards (B.I.S, 1978, reconfirmed in 1999) classification on climatic regions is found to be an ideal one for Indian climate. Accordingly, the study area falls under identified warm and humid region and fits well with the description and climatic data. The study is limited to warm and humid climate of coastal Karnataka in south India and the location of the case study is a broad representative sample of this region. The reference building consists of a heterogeneous mix of naturally ventilated and air conditioned office spaces. The offices are functional with the same operational schedule throughout the year. The building has a narrow floor plate and the natural cross ventilation may be well understood in such a layout.

The longer west facade of the building is upwind along the predominant wind direction from SW to NE, but solar radiation exposure is high, the longer axis being along N-S direction. This exposes most part of the building to the east and west sun with heat gains not suitable for the region's climate. This condition will help in understanding building envelope design in peak heat gain conditions. The baseline case model was created as per the existing specifications and on site documentation of the reference building. The model was simulated for thermal comfort and natural ventilation analysis using DesignBuilder software [11]. A thermal comfort survey was conducted in the reference building. As per the survey, the occupants of the fifth floor office space were found to have the maximum thermal discomfort and that office space was chosen as the baseline case. The simulated baseline case was further investigated with varying building envelope components and natural ventilation options including night ventilation to identify actions that could reduce indoor operative temperatures. DesignBuilder software has been chosen for analysis because it uses the latest EnergyPlus simulation engine which is validated to calculate a range of building performances [12]. Climatic analysis of warm and humid climate along coastal Karnataka revealed that March, April, and May to be warmest months. May being the most critical month in terms of percentage of office hours outside the thermal comfort zone, detailed simulations were carried on the peak summer day of that month. A typical day in the coolest month of August was also simulated to understand the impacts of varying building envelope components and natural ventilation. The results of field studies and simulation results have been analyzed to study the impacts of building envelope and natural ventilation on indoor thermal environment.

3. Simulation and Data Analysis

3.1. Climatic Data and Analysis

As climate is one of the main parameters affecting the energy behavior of a building, the effectiveness of a retrofitting intervention is strongly dependent on the climatic region of reference. As per the Bureaus of Indian Standards (IS 7896:2001) the weather data from the nearest weather station of Mangalore in coastal Karnataka as classified for the reference building location by Indian Metrological department (IMD) and Indian Society of Heating Refrigerating and Air Conditioning( ISHRAE) was taken for the study and simulation purposes (Fig 1).

Fig. 1. Site Climatic data at the reference building location

Coastal Karnataka has warm and humid climate with intense radiation on clear days. In summer, temperatures can reach as high as 30-35oC during the day and 25-30oC at night. In winter, the maximum temperature is between 25oC to 30oC during the day and 20oC to 25oC at night. The relative humidity is generally very high, about 70-90% throughout the year. Precipitation is also high, being about 1200 mm per year. The wind is generally along southwest to northeast direction with speeds ranging from extremely low to very high. Wind is desirable in the climate as it can

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cause sensible cooling of the body. As per ASHRAE Standard 55 adaptive thermal comfort, for the site location the upper bound indoor comfort temperature was found to be 29.4°C at 0.2 m/s, 31.6°C at 0.6 m/s and 32.6°C at 1.2 m/s. The environmental thermal comfort parameters are air temperature, mean radiant temperature, air speed and relative humidity.

Climatic Analysis indicates that the indoor temperatures in office buildings in the warm and humid climatic region of coastal Karnataka remain high during the summer months. The percentage of comfort hours during office hours for the month of May was plotted on the psychometric chart. The results showed that only 7.3% of the office hours to be in the adaptive comfort zone (Fig. 2) [13].

Fig. 2. Psychometric chart showing the percentage of comfort hours during office hours in the month of May.

3.2. Building envelope details and simulation of reference building

The reference building location and area details are listed as per Table 1. The building is free standing without obstructions from adjacent buildings (Fig. 3). The building envelope details are listed as per Table 2.

Table 1. Details of the reference building

Building Information Details

Location 13°20'58.5"N 74°47'14.8"E

Total area of the land 1178 m2

Total built up area 3130 m2

Ground floor plinth area 423 m2

Fifth floor area 423 m2

Building size G + 5

Building facing East

Operating Schedule 9.00am to 6.00pm (6 days/week)

Occupancy 1 person per 8 m2

Lighting power density 10 w/m2

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Fig. 3. View of the reference building showing the longer east facade and south facade.

Table 2. Building envelope details

Building Element Material Details

Wall Concrete Block + Cement plaster 200mm thick masonry wall + 15mm cement plaster on the internal and external surfaces

Roof RCC flat slab 150mm thick reinforced concrete slab

Floor RCC flat slab 150mm thick reinforced concrete slab

Surface Paint Cream color interior paint, light brown color exterior paint

Window type Glazing Clear Glass with 4 mm thickness

Window Frames Steel 100 mm

Fig 4. (a) Thermal imagery of the reference building on the peak summer day in the month of May; (b) Reference Building

The reference building receives a lot of heat throughout the daytime. The thermal imagery of the facade of the building was recorded using Testo instrument 870-2 for the peak summer day of May and the average surface temperature was found to be 41oC (Fig. 4). On site surface temperatures were recorded using Testo instrument 830-T1 and the derived indoor temperatures were found consistent with the simulation model.

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The office space on the fifth floor with both naturally ventilated and air conditioned spaces, was simulated with

DesignBuilder Software (Fig.5). The physical dimensions of the office space are 10m x 10m. The open office on the east side is 7m wide. Individual office cabins with window air conditioning systems occupy the western side of the office and are 3m wide. The open office has not been provided with window air conditioning. The height of the office space is 3.1m. The baseline office space has 40% window wall ratio on the east side, 20% window wall ratio on the west side and 30% on the south side. The north side is blocked due to adjacent office space.

Fig. 5. (a) Baseline case – Plan; (b) View of office space

The baseline case with existing information as documented during site study was simulated for thermal comfort analysis for the warmest day of the Typical Meteorological Year (TMY) on 1st of May. As per the onsite documentation, the masonry wall construction for the baseline case used 200mm concrete block with 15mm cement plaster on either side and with a combined U-value of 0.816 W/m2K. The roof is made of 150mm RCC slab and with

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a U-value of 2.483 W/m2K. A series of building model simulations were carried for 1st of May. The average indoor operative temperature of the non AC office space during occupied hours was found to be 35.96oC with maximum indoor temperature of 38.78oC at 6 PM (Fig.6). The indoor temperatures during the occupied office hours were much higher than the maximum adaptive thermal comfort of 32.6oC. August is the coolest month in the region and for the baseline construction the average indoor temperature was 35.79oC for 1st of August.

The existing office space has individual office cabins with partitions made of aluminum frame and 4mm glazing. When the partitions on the west side of the office space were removed and cross ventilation was facilitated between west and east window openings the average indoor temperature improved to 35.55oC (Fig. 7). When the cross ventilated office model was simulated after replacing the existing concrete block masonry wall with 200mm Autoclaved Aerated Concrete (AAC) block masonry with 40mm rock wool insulation and a combined U-value of 0.364 W/m2K the indoor temperature was 35.21 o C. When the RCC roof slab was also replaced with 200mm thick aerated concrete slab with a U-value of 0.658 W/m2K, the average indoor temperature was found to be 33.50oC (Fig

8). By providing a layer of rubber insulation of 75mm width on the roof slab with a combined U-value of 0.510 W/m2K the average indoor temperature improved to 33.37oC. The baseline case was simulated as per the operational schedule of the reference building and the windows were open only during the occupied hours between 8 am and 6pm. By allowing night ventilation to the above model the average indoor temperature further reduced to 32.8oC during the office hours (Fig 9). The model was also simulated for various shading options for the window openings. By providing 0.5 m overhang for windows, the average indoor temperature was 32.73oC. Increasing the width of the window overhang to 1m the average indoor temperature was 32.59oC and with 1.5m overhang the indoor temperature was 32.5oC. By providing the window openings with 0.5m overhangs and 0.5m side fins, the average indoor temperature was 32.73oC and with 1m overhang and 1m side fins it was 32.5oC (Fig. 10). For August 1st the model with 1m wide side fins and overhangs for the windows the average temperature was 32.12o C for the office hours.

Fig. 6. Baseline case simulation results for 1st of May

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Fig. 7. By removing the office partitions and promoting cross ventilation the average indoor temperature was found to be 35.55oC

Fig. 8. Use of autoclaved aerated concrete block wall with aerated concrete slab the average indoor temperature lowered to 33.5oC

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Fig. 9. By adopting night ventilation to the previous model the average indoor temperature improved to 32.88oC

Fig. 10: Providing window shading with 1m overhangs and 1m side fins, the average indoor temperature improved further to 32.5oC

3.3. Discussions on simulation results

The simulation results show very high indoor temperatures in the summer months, the maximum indoor operative temperature was 38.5oC at 4 pm on the peak summer day of 1st of May. At 8 am on 1st of May the indoor temperature was 31.65oC and the indoor temperature continuously rise during the office hours causing thermal discomfort in office spaces without mechanical cooling using air conditioning. The results also show that open office plans with natural cross ventilation reduced indoor temperature by 0.4oC from the baseline case. By using autoclaved aerated concrete blocks with insulation for masonry wall construction the indoor temperature improved by 0.75oC. By providing aerated concrete slab roof, the indoor temperature significantly reduced by 2.46oC from the baseline case. By providing insulation to the roof the indoor temperature further reduced by 0.13oC. This shows that control of heat gains through the building envelope is very important in this region.

When night ventilation was used, it was able to cool the thermal mass at night and the average indoor temperature during office hours was 32.88oC, with an improvement of 0.57oC from the previous model and 3.08oC lesser than the baseline case. The results prove the effectiveness of night ventilation as a strategy to improve indoor thermal environment. The most acceptable indoor thermal environment was achieved when the above improvisation strategies were used with 1m over hang and 1m side fins when the indoor temperature reduced to 32.5oC an improvement of 3.46oC. Window shading devices and side fins allowed natural ventilation but partially blocked direct solar heat gain entering office spaces. As per the climatic analysis, August is the coolest month in the region and on 1st of August with the above modifications to the building envelope design and promoting natural ventilation during the day and also at night, the average indoor temperature was found to be acceptable at 32.12oC and 3.22oC lower than the baseline average indoor temperature of 35.34oC for that day.

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The results can be summarized as follows, • Narrow floor plate and open office planning can be used to promote cross ventilation to improve indoor thermal

environment in the region. • Efficient construction of roof slab and masonry wall was found to be very beneficial in reducing indoor

temperatures. Use of insulation materials to the roof slab and masonry wall further improved indoor temperatures.

• Night ventilation is found to be very effective in cooling the thermal mass resulting in improved indoor temperatures during the daytime office hours. The office windows can also be kept open at night to allow natural ventilation. Windows can be provided with grilles for security and screens to protect from insects.

• Solar shading of window openings with overhangs and side fins improved indoor thermal environment by allowing natural ventilation and partially preventing direct solar heat gains.

4. Conclusions

India has proposed 100 new smart cities with several of them proposed in the warm and humid region. The current construction practices widely followed in the office buildings in warm and humid region of India causes thermal discomfort to its occupants and makes air conditioning cooling systems necessary resulting in high energy use and costs. This also increases the emissions of greenhouse gases contributing to climate change. This paper investigated the indoor temperature improvement potential in office buildings by simulating a typical office building in coastal Karnataka, India by modifications in masonry wall and roof slab construction and also by providing insulation. The model was further simulated for daytime and night natural ventilation, shading of windows by overhangs and side fins. The research reveals that careful attention to building envelope design, efficient use of materials and promoting natural ventilation can improve indoor thermal environment thus reducing the use and dependence of energy intensive air conditioning systems towards energy conservation and sustainable new developments in warm and humid climate.

Acknowledgements

We thank Manipal University for all the support towards this research. We also thank Prof. Raviraja Adhikari, Prof. Satish Shenoy, Prof. Nandineni Rama Devi, Prof. Udayashankar H.N, Prof. Naseer M.A and Prof. Lekha Hegde for providing insights and expertise that greatly assisted the research.

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