Development of a sustainable energy rating system for residential buildings in Sri Lanka

Abstract

Energy rating system can be considered as a key policy instrument that will assist the government to reduce energy consumption. Energy rating includes the direct bene ts such as, energy requirement and carbon dioxide emission reduction, cost reduction for the users, increase the public awareness regarding energy issues, and improve the availability of information regarding the building. The government of Sri Lanka also has identi ed the importance of energy performance of buildings and considers it as a strategy for the sustainable energy development of the country. Existing rating systems in the world only considered limited factors related to energy consumption and to provide more accurate rating system it is proposed that a more sustainable energy rating system should be developed considering all the criteria. This research is aimed at identifying the existing rating systems, investigate the existing systems, to identify the parameters required for determining the energy performance of residential buildings, to develop and equation for calculating the energy score and to develop a scale for comparing the energy performance of residential buildings in hot and humid climate in Sri Lanka. To achieve the above mentioned objectives, this research followed the concept of sustainable energy which comprises of both energy e ciency and renewable energy. The energy e ciency of a residential building needs to consider the energy e ciency due to building properties and energy e ciency of the occupants. To evaluate the energy e ciency of the building properties, the asset rating method was used where the building is modeled and the energy consumption for thermal comfort and lighting is calculated. Using 4569 di erent models (varying window to wall ratio, orientation, zone size, zone location, building shape and oor area), a parametric analysis was conducted to develop an optimum model which was then used as the reference value for the rst sub rating (Building consumption rate). A questionnaire survey was conducted to identify the factors a ecting the energy consumption of the Sri Lankan residential buildings and in total 336 lled questionnaires were used for parametric analysis. The questionnaire revealed that the number of bedrooms is not signi cant for energy consumption and the occupant characteristics and the equipment usage are highly signi cant factors. Therefore, when developing the occupancy behaviour rate, the average domestic energy consumption in Sri Lanka was used as reference, without normalising. To consider the renewable energy usage, another sub rating named energy source rate was developed and to decide whether to o set the energy consumption with renewable energy use or to use a separate index, another questionnaire survey was conducted with rooftop solar PV consumers. The results of the survey indicated ii that there is a strong rebound e ect due to the solar PV adoption and there are some other social and technical impacts as well. Therefore, when developing the energy source rate, a sustainability index was used and based on the percentage of contribution of the energy sources to the nal energy use the nal energy source rate was determined. These three sub ratings were normalised and brought to a common scale of 0 to 100. The sub ratings were integrated using weightages which were obtained using a perception survey of engineers, architects, quantity surveyors and facility managers in the industry. The application of the rating method is explained using two actual examples. Further, a sensitivity analysis was done to re ect the e ect of the changes in the parameters used in the score calculation equation using the rst sample house. The rating methodology proposed in this thesis can be used over any country or any building by changing the reference values and weightages. Keywords: Energy rating; energy e ciency; buildings; thermal comfort; renewable energy; energy labels; consumer behaviour