Effect of thermal mass and insulation on energy consumption of an exterior insulated passive solar dwelling

Abstract

The key building design factors that affect the energy flow in domestic buildings are: thermal mass, thermal insulation, solar aperture and orientation. This thesis investigates the effect of thermal mass and insulation on the energy consumption for space heating of a domestic building using a computer simulation package (CHENATH).

This study involves the comparison of the simulated energy consumption of two side-by-side test buildings, identical as near as possible except for the level of thermal mass in the walls. One is a passive solar test building (PSTB1), with exterior insulated concrete walls as heavy thermal mass. The other passive solar test building (PSTB2), has exterior insulated timber framed walls. It has been shown that in a continuous heating regime the monthly auxiliary heating energy consumption for PSTB2 is 1-16% greater than PSTB1 (3.9% for one typical year). In an intermittent heating regime it was shown that the monthly energy consumption for PSTB2 is 7.5-19% greater than PSTB1 (11.2% for one typical year). Moreover, it was shown that for the same wall R-value, as the wall thermal mass increases the energy usage decreases and approaches a constant value.

These test buildings were constructed and hourly temperatures and energy consumptions were measured to investigate the reliability of the computer simulation results. It was observed that CHENATH tended to under-predict the maximum daily internal air temperatures by 5-7°C on sunny days. In turn, CHENATH significantly over-predicted the heating energy requirement. The reasons for such disparities between the predicted and measured results, and what could cause the simulated heating energy to be consistently higher than the measured ones, are discussed. Even though CHENATH has not produced correct results for these test buildings, it demonstrates the relative performance of the effect of thermal mass and insulation.