A finite-difference model is used to simulate the effects of thermal mass on thermal load. A sinusoidal function is used to simulate the exterior air temperature. The interior air temperature set point remains constant. The mechanism by which thermal mass affects thermal load is described. Equations are given to calculate thermal load as a function of the exterior air temperature amplitude, the temperature above and below the mean temperature. Equations are given to calculate the minimum thermal load resulting from thermal mass and therefore the maximum thermal load reduction with thermal mass.

Equations and methods are given to calculate the minimum thermal load resulting from thermal mass from weather data files, TMY or TMY2 files. A design equation is given as a guideline to determine the amount of thermal mass required to reduce the thermal load with given weather conditions.