Describes the use of a mathematical model of a heat pump to determine how the design of the outdoor air-coil (evaporator) affects the heating performance of an air-to-water heat pump, taking both compressor power and fan power into account. Shows that the optimum performance for frost free conditions is achieved using an evaporator of large face area, minimum depth, minimum fin spacing, low airflow rates, as high an evaporating temperature as possible and no superheat across the coil.

KEYWORDS: year 1996, Heat pumps, designing, calculating, performance, air conditioning, evaporators, air water heat pumps