Shifting costs and availability of different energy resources and design the improved of heat pumps have led to their almost exponential increase in use. Within the Unit7d States, 82,000 units were shipped in 1971, increasing to 300,000 in 1977 and 547,694 in 1979 (according to ARI 1979 statistics).

The rating Coefficient of Performance (COP) values for heat pumps are at fixed rating conditions (ASHRAE Standard 37-69), which up to now have only considered steady state conditions. (Standards for cyclic testing are being drafted through ASHRAE Standard Project Committee 103.1 and most probably willbe based on NBS-DOE proposed rulings.

The work now reported is based on the master theses of Hart (1978), Sanchez (1975), white (1975), and Murphy (1977). The work of these four led to an acceptable model for heat losses in the home. An hour-by-hour, steady state model receives, as an input, the outside weather conditions and gives, asan output, the hourly heating load.