The effect of variations in convection coefficients on thermal energy storage in buildings Part II — Exterior massive walls and simulations

A theoretical study has been performed to determine the effect of variations in convection coefficients on the storage of thermal energy in structural materials in the exterior envelope of buildings. Detailed analytical and numerical analyses have been performed to study the fundamental aspects of the problem for simple geometries. Based on the detailed analyses, a thermal energy storage effectiveness parameter has been defined in terms of the changes in heating and cooling energy requirements of a single-zone building in response to the introduction of mass in its exterior walls. Calculations of the exterior wall effectiveness have been made to investigate the effect of variations in convection coefficients at the interior surface of external envelope materials, as well as the influence of additional building parameters, such as internal loads, interior air temperature control strategy, and internal mass.

To extent the results of the detailed analysis and to study the effects of variable convection coefficients on heating and cooling energy requirements in real buildings, simulations of two prototype residential buildings (in Mexico and the United States) have been performed using the building energy analysis computer program BLAST. Results indicate that the energy consumption of a typical uninsulated Mexican residence is quite sensitive to the variations in convection coefficients commonly occurring in buildings (a difference up to a factor of three over the range 0.5 ⩽ h ⩽ 10.0 W/m²K). Buildings energy consumption of a typical well-insulated U.S. residence is less sensitive to variations in convection coefficients, although for some climates the effects are still significant (up to a 40% increase over the range 0.5 ⩽ h ⩽ 10.0 W/m²K). Since the convection coefficients at interior building surfaces vary quite widely within this range, this work suggests that for some climates and building constructions, improved characterization of convection coefficients is needed to permit reliable calculation of the energy requirements of buildings incorporating large amounts of thermal mass.