Impact of air infiltration rate on the thermal transmittance value of building envelope

Abstract

Building envelope plays a crucial role in limiting the heat gains and affects the energy requirement for space cooling directly. To this end, building codes specify overall thermal transmittance values of the building envelope to address the building energy efficiency. However, these values do not consider the heat gains due to infiltration, which is a characteristic of the building envelope. With this context, the objective of this research is to measure the infiltration rates in apartments and propose an infiltration factor to revise the existing equation of the residential envelope transmittance value (RETV), recommended by the building code in India. Herein, the Blower door method is employed to measure the infiltration rates for a total of 20 air-conditioned apartments. Such a study, with the blower door method, has not been reported in India. The measurements show that the infiltration rates vary from 0.53 ACH to 1.63 ACH and are correlated with the window construction characteristics. Simulations are also carried out for estimating the impact of infiltration on the RETV with a calibrated energy model. The sensitivity analysis showed that the heat gain from infiltration accounted for 10%–33% of the overall envelope heat gains. The infiltration factor is derived for different climate zones of India by carrying out a parametric study involving 3072 simulation cases. It was found that 1 ACH of infiltration contributes 5.46, 4.22, and 3.53 W/m2 of RETV in hot-dry, composite and warm-humid climate respectively. A relationship between revised RETV and energy consumption is also established.