Optimum level of insulation for energy efficient envelope of office buildings

Building envelope plays an important role in energy efficiency of the buildings as it is the only permanent source of energy efficiency. A well-designed building envelope reduces the demand of HVAC and lighting load. When insulation is provided in the building envelope, it further enhances the energy efficiency. Therefore, it is important to create thermal resistant building envelope considering both the energy consumption and the associated costs. Thermal insulation has a considerable positive effect on reducing the heating and cooling energy demand. It is seen from the tests conducted by Nasrollahi and Nooraei (2013) for design of energy efficient and cost-effective office buildings that initial increase in insulation reduces the heating/cooling load but beyond a certain limit, there is no substantial effect of reduction in heating/cooling load with increase in insulation indicating that there is an optimum value beyond which insulation has no substantial effect on reduction in heating/cooling load. Therefore, the paper attempts to find out this optimum level of insulation so that the building envelope is cost-effective and energy efficient. Three case studies of energy efficient LEED (Leadership in Energy and Environmental Design)/GRIHA (Green Rating for Integrated Habitat Assessment) certified buildings have been considered to determine the optimum level of insulation. In the analysis, comparison has been made between U-values of various components of the building envelopes of three case studies with the U-values prescribed by Energy Conservation Building Code (ECBC)-2007 for various components of the building envelopes based on daytime or 24-h usage, and location of the buildings in composite/warm and humid climate zones. Thereafter, results obtained from the analysis have been compared with the optimum U-values derived from the tests conducted by Nasrollahi and Nooraei (2013) to arrive at the optimum level of insulation. The optimum level of insulation has been found to be 30% above U-values prescribed by Energy Conservation Building Code.