Life Cycle Energy Analysis of a Multifamily Residential House: A Case Study in Indian Context ()
1. Introduction
A large number of buildings are built for residential, commercial and office purposes every year all over the world. Building construction sector experiences fast paced growth in developing countries, like India, due to growth economy and rapid urbanization. Worldwide buildings consume 30% - 40% amount of primary energy in their construction, operation and maintenance and held responsible for emitting 40% of global warming gases [1]. In India, 24% of primary energy and 30% of electrical energy is consumed in buildings [2]. Since, buildings are consuming large amount of energy; they need to be analyzed in the lifecycle perspective to develop strategies for reduction of their energy use and associated environmental impacts, and make them sustainable. Life cycle assessment (LCA) is the state of art tool in assessing the sustainability of buildings. In order to assess the environmental impact, it is necessary to perform an inventory analysis of building materials and the process of construction, and demolition. But, building materials production processes are much less standardized because of the unique character of each building. There is limited quantitative information about the environmental impacts of the production and manufacturing of construction materials, and the actual process of construction and demolition particularly in developing countries like India.
Life cycle energy analysis (LCEA) of buildings can also give a useful indication of environmental impacts attributable to buildings, if energy use of the building is expressed in primary energy terms. The analysis also helps in identifying the phases of largest energy consumption and to develop strategies to make buildings sustainable. Life cycle energy analysis is an approach that accounts for all energy inputs to buildings in their life cycle. It includes direct energy inputs during construction, operation and demolition of building, and indirect energy inputs through the production of components, materials used in construction (embodied energy). LCEA has been applied to examine the relationship between embodied energy in construction materials and operational energy and also to analyze the influence of building characteristics like frame work, construction, thermal insulation, heat recovery etc., on life cycle energy use of residential houses in Sweden [3,4]. Winther and Hestnes [5] compared life cycle energy use of different versions of a residential building, containing varying active and passive energy saving measures, with that of conventional building in the Norwegian context. Citherlet and Defaux [6] analyzed and compared a family house by changing its insulation thickness and type, type of energy production system and use of renewable energy in Switzerland. Mitraratne and Vale [7] recommended provision of higher insulation to a timber framed house as energy saving strategy for low energy housing in New Zealand context. Treloar et al. [8] and Fay et al. [9] analyzed the life cycle energy of Australian residential buildings built in Melbourne. Utama and Gheewala [10] analyzed clay and cement based single landed houses in Indonesia. In Indian context Shukla et al. [11] evaluated embodied energy of an adobe house. Reddy and Jagadish [12] estimated the embodied energy of residential buildings using different construction techniques and materials. Debnath et al. [13] evaluated embodied energy of the load bearing single storey and multistory concrete structured buildings. It can be observed that studies limited to embodied energy analyses of buildings are reported in open literature in Indian context. However, in order to understand the total energy needs of the building, complete life cycle energy analysis covering all phases of its life cycle is required. Only recently, the authors have reported on life cycle energy analysis of single family residential houses [14,15].
In the present work an attempt is made to present life cycle energy profile of a multifamily residential building covering the embodied, operational and demolition energy aspects in the Indian context. Some energy saving measures have also been examined from life cycle energy perspective. A typical multifamily residential house (Figure 1) called as International House (I H), located in the campus of the Motilal Nehru National Institute of Technology (MNNIT), Allahabad, India is selected for the study to gain insight into the life cycle energy use of the residential house in Indian context. The study covered energy for construction, operation, maintenance and demolition phases of the building. India is a sub tropical
Figure 1. Case study building in Allahabad, India.
Figure 2. Climatic zones in India (Bansal, 2007).
country with 5 climatic zones viz: hot and dry, hot and humid, moderate, temperate and cold (includes cold and sunny and cold and cloudy climates) and composite (Figure 2). Allahabad falls in composite climate and is located at 25.45˚N latitude and 81.84˚E longitude. Allahabad experiences three seasons: hot dry summer, cool dry winter and warm humid monsoon. The summer season lasts from April to June with the maximum temperatures ranging from 40˚C to 45˚C.
Monsoon begins in early July and lasts till September. The winter season lasts from December to February. Temperatures rarely drop to the freezing point. Average maximum temperatures are around 22˚C and minimum around 10˚C.
2. Case Study
The selected building is a 4-storey concrete framed structured multifamily residential house comprising 44 apartments (Table 1). The material used for the building structure is reinforced cement concrete and envelope is made from brick masonry. Each flat consists of bed room, living room, kitchen and restroom in the floor area of 40 m2. The calculated U-values (includes outside air film for exterior surfaces) using e-Quest simulation software [16] for various elements of the building are listed below:
• Roof: 5.08 W/m2 K;
• Ceiling: 4.73 W/m2 K;
• Window: 10.85 W/m2 K;
• External wall: 2.15 W/m2 K;
• Ground floor: 5 W/m2 K.
The electricity from the national grid is the only oper-
Table 1. Basic parameters of the case study of residential building.
ating energy used by the building systems. Bed room of the building is air conditioned using window air conditioner. The indoor operating set point temperature is around 25˚C and all lighting controls of the building are manual. The life cycle energy of the selected building is evaluated based on an assumed service life of 75 years.
The system studied included the manufacture of building materials, construction, operation and maintenance, and demolition phases. The transportation for each life cycle stage is also included. All the materials are manufactured in India. Embodied energy coefficients of building materials are taken from Indian literature [11-13,17, 18], and are shown in Table 2. The main information on the types and quantities of materials as well as components of the building is obtained from the detailed estimates of the building, technical specifications and other relevant documents from the building consultant.
3. Life Cycle Energy (LCE)
Life cycle energy of the building is estimated by summing up the energy incurred for construction (initial embodied), operation, maintenance (recurring embodied) and finally demolition of the building at the end of its life.
3.1. Initial Embodied Energy
Embodied energy of the building materials are obtained by summing up the product of quantity of materials multiplied by their embodied energy coefficients (Table 2). Energy for construction included energy (electricity) used for lighting, water lifting and diesel fuel used by construction equipment at the site. These are subse-
Table 2. Quantity and embodied energy of materials used.
quently aggregated with energy consumption for the transportation of building material to the construction site. The main building elements are building frames (beams, columns), slabs, floors, staircases, foundation, walls, windows, and finishes. Items such as fitments, sanitary fixtures, appliances, electrical and external items are excluded from the study due to the difficulty associated with obtaining their embodied energy data. All data relevant to construction machines and equipment used on site and transportation distances of construction materials to the construction site are obtained from the available records.
3.2. Building Operation
Operating energy of the building includes electrical energy used for cooling, heating, ventilation, lighting (6 W/m2 for 100 lux), miscellaneous equipment operation and water supply. This is calculated by simulation through e-Quest energy simulation software [16].
Figure 3 shows 3D model of the building. The building is partially occupied during day time between 9.00 am to 5.00 pm and is fully occupied during night time and fully operated during weekend i.e., Saturday, Sunday and other public holidays. Comfort indoor air temperature is set as 25˚C for cooling and 18˚C for heating. Coefficient of performance (COP) of window air conditioner is taken as 3 for cooling and 0.9 (taken as a conservative value) for electrical resistance heating. Thus, calculated annual electrical energy demand of the building for its operation (Figure 4) is then converted to primary energy using primary energy conversion factor. In