Solar and Internal Gain Adjustments in Calculation of Energy Conservation Savings

Heating degree days are often used as a climatic measure in building energy calculations. To account for the effects of solar and internal gains, degree days at a lower base temperature are sometimes used, or the number of degree days is adjusted downward by a degree-day correction factor. In this paper, we present a theoretical derivation which demonstrates that ASHRAE Cd factors are not theappropriate correction factors for calculation of energy savings from envelope conservation measures. The results of this derivation can be used to develop new correction factors appropriate for savings calculations.