«CSAAR (7: 2010: Amman) Sustainable Architecture and Urban Development \ Edited by Steffen Lehmann, Husam Al Waer, Jamal AI-Qawasmi. Amman: The Center ...»
1 Introdnction Bangladesh with an area of 55,598 square miles is a small but one of the most densely populated eountries in the world. The population of Bangladesh was estimated at 129,194,224 in July of 2000 (Eneyclopaedia of the Nations, 201O).The climate of Dhaka ean be categorized as tropieal monsoon type with high temperatures, high humidity most of the year, and distinetly marked seasonal variations in preeipitation, The energy infrastructure of Bangladesh is quite smalI, insuffieient and poorly managed (Temple in Mozumder and Marathe, 2007). 82% of the eountry's eleetrieity is generated from natural gas, 9% from oil, 4% from hydro and 5% from coal (Tuhin, 2008). According to Tuhin (2008), only 42% of the population i5 served with eleetrieity and per eapita electrieity use is about 160 kWh. The demand for eleetrieity is growing at a rate of 10% per year (USAID in Mozumder and Marathe, 2007) without any well-designed plan to meet the demand. Aecording to the report of Dhaka Mirror (2009), the eountry has been experieneing a shortfall of about 1200 MW of eleetricity against the demand of 4500 MW. Dhaka alone i5 being provided with 1185 MWs against a demand for about 1800 MWs.
Worldwide, 30% to 40% of all primary energy is used in buildings (UNEP, 2007). Energy efficieney in residential buildings is erueial, espeeially for a eountry like Bangladesh where the demand for eleetrieity, as already stated, is growing at a rate of 10% per year. Aceording to BBS (2008), the eleetrieity used by the industrial, residential, eommereial and other seetors in the year 2006-2007 was about 21181 GWh. Out ofthis, 42% was used by the residential see tor alone (BBS, 2008). Mueh of the inereased demand for eleetrieity is due to the inereased standard of living (People's Report 2004-2005, 2006) among the wealthier ineome groups. One of the major faetors in the inereased use of electricity by the high er income group is the use of air eonditioning units, whieh has only recently become quite popular (Haneoek, 2006). To make matters worse, a study of the regulations in the national building code of Bangladesh shows that the govemment of Bangladesh has not adopted building energy codes in any form for building eonstruetion. In addition, simple observation of most of the residential buildings in Dhaka shows that developers, architeets and interior designers are still not aware of the role they ean play in designing energy effieient buildings.
The aim of this study is to identify passive energy efficient features for residential buildings in the eontext of tropieal climates such as Dhaka to make a eontribution in the field of arehitecture, by developing and designing energy efficient residential buildings. Given the speeifie problems in the preceding section, it ean therefore be attributed that there are probably large potentials for improvements in the energy seetor and built environment. However, this Sustainable Architecture and Urban Development 185 research focuses on those attributes that can be attained through changes in the practices of architects. This study, based on a case study residential building in Dhaka, is thus expected to answer the following research questions in order to
achieve the goals ofthis study:
I. What is the present electric energy use for cooling and lighting typical residential buildings inhabited by upper middle income households in Dhaka?
2. What are the passive design features that can be incorporated in residential buildings of Dhaka to make them energy-efficient?
3. What are the possible energy savings in the case study residential building by adopting these energy eft1cient features?
In terms of the various categories of buildings that are there in Dhaka, this research was delimited to a case study on multi-unit residential buildings and not on a statistical sampie. This study confined itselfin considering energy use at the operational phase of the building. The study was oriented towards the residential buildings inhabited by upper middle-income groups in Dhaka. This study is delimited to the upper middle-income group, since they use more and more energy as they have increased their standard of living and are becoming increasingly accustomed to the use of air conditioners. The study is restricted to making new residential buildings energy-efficient and does not consider the existing housing stock. Reza (2008) notes that Dhaka city, with an annual growth rate of about 4%, adds half a million people to its population each year. He also states that to accommodate the growing population, the city would need at least 10 million new units/flats by the year 2015 and thus, Dhaka would not be able to cater the energy needs ofthese new units.
2 Methodology 2.1 Research Methodology This research is based on a single case study and through literature review to explore the problems specified and seek answers to the research questions. A literature review consisting of books, journal papers, researches and documents defined the theoretical framework for this study by identifying energy efficient design principles that could be used for the context of Dhaka. In addition, it identified the methodology of analysis and issues that were investigated in the case study. The case study is a multi-unit residential building that is representative of inefficient energy buildings in Dhaka city. A fieldwork in Dhaka consisted of visits to the case study building and interviews with the residents. Quantitative and qualitative data were collected from the case study building. The data on energy use of different flats/units in the building were analyzed quantitatively and the design features of the apartment were analyzed both quantitatively and qualitatively. Energy efficient principles that were identified through literature review were summarized and analyzed quantitatively Tahmina Ahsana & Svaneb to determine the energy savings of all the features that eould be applied in the eontext of Dhaka. Calculations were then made to see how mueh energy the flats surveyed in the ease study building eould save, by adopting the energy effident design prindples.
2.2 Selection of case study
The seleetion of the ease study building was based on the following eriteria:
• It is representative of typieal multi-unit residential building design in Dhaka • The arehitectural drawings of the apartments were available • It was aecessible • The households were eooperative.
2.3 Issues Investigated Apart from the design aspects that were identified in the theoretical framework,
the following issues in the case study apartment have also been investigated:
• energy use praetices of households (appliances used, energy used by those applianees) • energy use for cooling and lighing in typical multi-unit residential buildings of Dhaka • general living pattern of the households
2.4 Data gathering strategies
Data gathering strategies were divided into a mixture of qualitative and quantitative approaches. The following different combinations of data gathering
strategies were adopted:
• qualitative and quantitative physical survey ofthe case study building • qualitative and quantitative semi-structured interviews that have open and c10sed questions • quantitative calcuJation of energy use • qualitative and quantitative arehitectural drawings of the case • archival records of computerized quantitative statistics on the climate of Bangladesh • quantitative statistics from newspaper c1ippings.
• photographs (qualitative and quantitative) Sustainable Architecture and Urban
3 Theoretical Framework3.1 Energy efficient residential buildings
Well-designed energy efficient buildings maintain the best environment for human habitation while minimizing the cost of energy. According to the Development and Land Use Policy Manual for Australia (2000), the objective of energy efficient buildings is are to improve the comfort levels of the occupants by reducing energy use for heating, cooling and lighting. United Nations (1991) defines energy efficient buildings to have minimum levels of energy inputs.
3.2 Basic principles in energy efficient building design
lt is evident frOl;n the above section that energy efficiency in buildings is vital for many reasons. Having justified the needs for energy efficiency it is now important to focus on the basic principles that can bring about energy efficiency in residential buildings of Dhaka. An extensive literature review consisting of different journals, books, researches and related websites was undertaken to establish the basic passive principles for designing energy efficient residential buildings. lt must also be stressed that as this study focuses on those passive that quantify the energy savings. Below is the list of aspeets for energy efficient residential buildings that show a pereentage reduetion in energy use and that has
been arrived at from the literature review and is based on the eontext of Dhaka:
• External wall
• Shading deviee
3.3 Building Envelope
3.3.1 External wall The field measurements and eomputational energy simulations to examine the effeetiveness of passive climate control methods such as facade eonstruction in a typical 14 storey residential building ofSingapore by Wong and Li (2007) reveal that the use ofthicker eonstruction on east and west external walls can reduce the solar radiation heat gain. It was [ound that the cooling load ean be reduced by 7%-10 % when the thiekness of external wall is doubied (229 mm eoncrete hollow block instead of 114 mm concrete hollow block).
Residential buildings in Dhaka have 125 mm thick external walls made of brick to make most of the floor area and to reduce construetion eosts. It should be noted that oider buildings had thicker walls ranging from 250 mm to 500mm.
With the advent of multi-unit residential buildings due to increasing pressure on building land and structural system, these thick walls were replaeed with 125 mm walls. The design option put forward by Wong and Li uses eonerete for external walls, but concrete is expensive in Dhaka. The loeal building material Svaneb Tahmina Ahsana & for external walls in Dhaka is burnt brick and it is much cheaper when compared to the cost of concrete. According to Gut and Ackerknecht (1993), the transmittance value or U value (measurement of heat transfer through a given building material) of 250 mm hollow concrete block whitewashed externally is
1.7 W1m2 • The U value of a 280 mm brick wall (115 mm brick + 50 mm air gap + 115 mm brick) induding an air cavity of 50 mm and whitewashed externally is also 1.7 W1m2 • These U values suggest that energy savings from using brick instead ofusing concrete should be roughly the same as calculated by Wong and Li. Hence, for Dhaka's context 280 mm brick walls including an air cavity of 50 mm can be used instead of hollow concrete blocks on east and west facades to reduce energy use.
3.3.2 Roof The roof is an important element of design when it comes to conserving energy because this part of the building receives most of the solar radiation and its shading is not easy. Nahar and Sharma in Tang and Etzion (2004), Vijaykumar et aL (2007) and Alvarado and Martinez (2008) conclude that the heat entering into the building structure through roof is the major cause for discomfort in case of non air-conditioned building or the major load for the air-conditioned building.
Vijaykumar and Srinivasan in Vijaykumar et al. (2007) have advised the use of hollow day tiles (HCT) in place of weathering course for roofs. They have claimed that the use of such a system can save 18% - 30% of energy used in an air conditioned building. Application of hollow day tiles as suggested by Vijaykumar and Srinivasan is easily feasible in the residential buildings of Dhaka as the cost ofhollow day tiles is not significantly higher compared to the cost ofthe weathering course for roofs.
3.3.3 Windows 18.104.22.168 Shading device Ossen et al. (2005) carried out a study using computer simulation to explore the effect of six different alternatives on incident solar radiation, transmitted solar heat gain, natural light penetration and energy use.