The air-to-air heat pump is recognized as a potentially efficient way to heat and cool residences. Many of the applications in the past have been in climates where cooling loads predominate. As a consequence, the customary method of sizing heat pumps has been on the basis of a design condition cooling load. Auxiliary heat has been added as necessary to make up any heating deficiencies during the heating season.

Recently there has been growing interest in using heat pumps in climates where heating loads predominate, traditional work and also in combining heat pumps with solar energy systems. Concurrently, there has been an increasing need for evaluations of the thermal and economic performance of these heat pump systems. A simplified and accurate method for predicting the thermal perfor- mance of air-to-air heat pumps in residential applications forms the subject of- this paper.