SIMULATION OF ELECTRICITY CONSUMPTION FOR NEWLY BUILT RESIDENTIAL BUILDINGS IN LAHORE
Fariha Saeed*
Syed Tauseef Ahmed**
Arif Qayyum Butt***
ABSTRACT
This paper assesses the electricity consumption trends in newly built residential buildings in Lahore, Pakistan. The aim is to establish guidelines for the construction of sustainable residential buildings in future. For this purpose thermal performance of a typical residential building in Lahore is evaluated with regard to electricity consumption while using a computer simulation programme. At next step a different set of specifications for the building envelop are applied as a typical residence to manage electricity more efficiently. Finally, a set of recommendations and guidelines are put forward to conserve electricity in residential buildings of Lahore.
Keywords: Sustainable architecture, Residential buildings, Energy efficiency, Cooling Loads, Comfort Level
1. INTRODUCTION
It is now clearly evident from the research studies that gradual rise in temperature and changes in climate in various parts of the world are due to the green house gase emission by the use of fossil fuels (Pachauri and Reisinger, 2007) for electricity generation. Therefore, it is necessary to device mitigation strategies in order to avoid dangerous consequences for future generations. One of the major strategies adopted all over the world is the design and construction of energy efficient buildings, particularly residential buildings (B.
Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer, 2007). Due to the rapid growth of population in Pakistan, housing sector is also expanding. In addition there is a severe electricity crisis from the last decade due to gap between supply and demand (WAPDA, 2009). There is a need to adopt electricity conservation strategies in all sectors of economy other than increasing the supply. However, the matter of energy efficiency in residential buildings has not
been given due consideration in their design as compared to other countries. In this paper it is suggested that energy efficient architecture is urgently needed in Pakistan. Architects in Pakistan should adopt climate responsive design techniques to minimize a buildings energy consumption. The current status of the building sector in Pakistan is discussed in the first section in terms of sustainability. Research methodology adopted is discussed next. Detailed description of the residential building, selected as a base case is provided.
Electricity consumption within the selected residence is then investigated. A number of modifications in the material specifications for the building envelop are then suggested and potential savings in electricity consumption are predicted using computer modeling. In order to increase energy efficiency in residential buildings in Pakistan recommendations are provided.
2. SUSTAINABILITY AND BUILDING SECTOR IN PAKISTAN
Generally the concept of sustainability encompasses environmental, economic and social responsibilities. In recent years sustainability issue in architecture have been recognized as very important due to ecological and energy considerations. Emphasis on climate responsive architecture is hall mark of sustainable buildings. It means an understanding of natural sources and systems and their interaction with the building environment is important to achieve comfort conditions within the buildings. For example, the placement of a window in a sustainable building is of the greatest importance as it could provide effective natural light, comfort cooling and ventilation (Kamyar Tolou Behbood1, Mohammad Taleghani and Shahin Heidari, 2010). It appears that such strategies are not adopted in residential buildings in Pakistan. As a result air conditioning is increasingly being used to achieve comfort conditions within the buildings. Approximately 60% of the electricity
* Fariha Saeed, Assistant Professor, Department of Product Design, University of Engineering & Technology Lahore
** Dr. Syed Tauseef Ahmed, Professor, Department of Architectural Engineering & Design, University of Engineering & Technology Lahore
*** Dr. Arif Qayyum Butt, Professor, Department of Product & Industrial Design, University of Engineering & Technology Lahore
consumed in residential buildings is used for this purpose.
In Pakistan, the residential sector is expanding rapidly due to population growth and increased urbanization. It also consumes more than 50 per cent of the countrys electricity produced (Energy Consumption in Pakistan, 2009). The present day residential buildings appear to be highly energy intensive as compared to vernacular buildings, which used local resources, and the use of passive strategies. The electricity generation in Pakistan is largely dependent on fossil fuels, (Energy Consumption by Source, 2006), irrespective of the fact that abundant renewable energy sources are available. However, the use of sustainable energy technologies is non-existent in Pakistan (GoP, 2006). Building Conservation Codes to conserve energy in buildings are in use in countries such as USA, Britain, India, Brazil and China. Though such codes have been proposed in Pakistan, however, they have not yet been legislated.
3. METHODOLOGY
An attempt is made in this paper to investigate the potential savings in electricity use in residential buildings in Lahore, Pakistan. A semi detached single family house was selected as a base case for this research. The electricity needed to maintain indoor comfortable conditions within the selected residential building was analyzed using Ecotect Analysis 2010 programme. It is an ideal tool for comprehensive energy simulation of buildings at an early stage of design.
Real hourly weather data for Lahore was used for the simulation. A model for the base case was in the computer software. The electricity needed within the building for maintaining comfortable indoor conditions was analyzed on yearly basis, based on heat gains through building fabric.
4. THE BASE CASE BUILDING
The residential building that is selected as base case is located in Lahore City, which is the capital of Punjab province and the second largest city in Pakistan (latitude 35_500N and longitude 74_300E. It has been built recently in a relatively new residential district, Wapda Town.
The climate in Lahore is composite, with four seasons.
Detailed information with regard to elements of climate in Lahore throughout the year is shown in Figure-1.
The base case residential building consists of two stories.
The total area of the plot is 2275 Sft. and it has covered area of 3040 Sft. Floor plans of the base case residential building are shown in (see Figure-2). The details of materials used in the building fabric are traditionally used in residential buildings in Lahore, Pakistan. These materials and their thermal properties are shown in Table-1.
Figure-1: Diurnal averages of temperature and solar radiation levels in Lahore on monthly basis
Figure-2: Plans of the Case Study residential building
Figure-2a: Temperatures of the case study residential building
5. ANALYZING THE BASE CASE BUILDING 5.1 Electricity Use
The electricity consumption in the base case building was analyzed with the help of simulation software Ecotect Analysis 2010.The simulation results for the electricity use on one of the typical summer days of the year in Lahore (i.e. 15 June) are plotted in Figure-3. This graph shows temperatures (in _C°) at the left side, with solar radiation scale (in W/m²) at the right side. The temperatures shown are the outside temperature, solar radiation and their impact on indoor temperature of the spaces within the buildings.
For instance, the graph shows the direct solar gains through the building envelop have highest impact on the interior spaces during the late afternoon due to time lag of the building components. Therefore, the inside temperature remains high even when outside temperature falls down.
The electricity use within the building was also examined throughout longer timeframes, e.g. weeks, months and year.
Next, the energy use within the building was simulated for a whole year, using actual climatic data.
The simulation results show that the annual electricity use for maintaining inside comfortable conditions within base case building is 39313 KWh per year, which appears to be
high when compared with standards as provided in the International Energy Conservation Codes for residential Buildings. In order to authenticate these results electricity bills for the base case building were obtained to compare the actual readings with simulation results. The simulation result appears to be in agreement with actual readings obtained from utility bills for the year 2011 which is 37114 KWh (Table-2).
Table-1: Building Components, Construction Materials and Their Thermal Properties
Table-2: Actual Readings of Electricity Consumption from electricity bills
It is clearly evident both from the simulation and actual readings that a large amount of electricity is being consumed in summer in residential buildings to maintain comfortable indoor temperature. Major reason for this high consumption appears to be inadequate insulation for the building envelop.
In other words a substantial amount of electricity used to maintain comfortable indoor climatic conditions in residential buildings can be saved by application of appropriate materials for the construction of building envelop.
6. IMPROVING THE ELECTRICITY CONSUMPTION IN THE BASE CASE BUILDING
6.1 Electricity Use
During the early stage of design, a number of passive strategies need to be considered to conserve electricity in residential buildings. Such strategies include improving the thermal mass or insulation of the external walls and roof, use of double-glazed windows and shading devices.
With such improvements in material specifications for building fabric, the simulation results showed much improvement with regard to electricity efficiency, as described later. The 9 thick external Brick masonry walls were replaced with 11 ½ thick cavity walls with 2 air cavity, resulting in a decrease in the Thermal Transmittance (U-value) for the external walls from 1.840 to 1.380 W/m2. An addition of a layer of polyurethane insulation 2thick to the top roof led to a reduction of thermal transmittance for the roof from 1.660 to 1.160 W/m2 K. In addition, single glazed windows
with aluminum frame were replaced with double glazed windows.
The building model of the base case residential building was again simulated with the changes mentioned above.
The indoor thermostat set points were the same as in the first simulation.
Table-3: Simulation Results of the case study with Modifications
Figure-3: Heat Gains for the whole year in the case study building
It is important to mention here that the reduction of the use of electricity appears to be due to the changes made in materials for the building envelop. These changes seem to be resulted in reduced heat gains as compared to the original base case building. The annual electricity use for the building was calculated to be around 21459 kWh. It means an approximate 45% reduction in electricity annually as compared to the base case buildings. It is a substantial improvement.
7. Guidelines for Energy efficient Residential Buildings in Pakistan
Based on the above analysis, with regard to electricity use in residential buildings, the following guidelines will help to achieve significant energy efficiency in residential buildings, particularly in areas with composite climate in Pakistan:
·
There is strong need to adopt passive strategies for energy efficient design of new residential buildings.·
It is also essential to use sufficient insulation in the buildings envelop. Building materials with good thermal insulation properties should be selected for building envelop.·
The appropriate external shading devices should be used to protect residential buildings from direct solar radiation. The proper design and location of shading devices is necessary to minimize the adverse impact of solar heat gains, and to utilize natural light for interiors. It will reduce the use of artificial lighting during the day time. Windows should be open able to facilitate ventilation during night in summer to create comfortable indoor conditions and lessen the use of air-conditioning.·
It is also suggested that energy-efficient appliances and lighting equipment should be used in new residential buildings in order to further reduce the electricity consumption.REFERENCES
B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds), Climate Change 2007; Mitigation of Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
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Kamyar Tolou Behbood1, Mohammad Taleghani2 and Shahin Heidari, Energy Efficient Design Statrategies in Hot dry Area of Iran: Kashan, Emirates Journal for Engineering Research, 15 (2), 85-91 (2010)
Pachauri, R.K. and Reisinger, A. (Eds.), Climate Change 2007: Synthesis Report, IPCC, Geneva, Switzerland. pp 104 Water and Power Development Authority (WAPDA), Power Wing, Projected Energy Demand vs Capability 2009-2030, Glossary of units
1. Watt (W)
The SI derived unit of power. Power is the rate at which work is done, or the rate at which energy is expended. One watt is equal to one per .
2. Watt hour (Wh)
A unit of work or energy, representing the energy delivered at a rate of one watt for a period of one hour.
3. Kilowatt hour (KWh)
A unit of work or energy, representing the energy delivered at a rate of one thousand watt for a period of one hour.