Feb. 05, 2007 – Twelve variable-speed capacity controlled air-to-air heat pumps have been evaluated by laboratory measurements and the results have been compared to similar investigations made in 2001 (variable-speed capacity control) and 1991 (single-speed compressors). The heat pumps were evaluated in terms of efficiency, performance of defrost system and ability to operate in a cold climate.
The results show that heat pumps have become more efficient since 1991 and 2001. On average, the coefficient of performance (COP) has increased by 7-24 % since 1991. The defrost systems have also improved, although there are still systems that in practice operate under simple time control, and thus perform unnecessarily many defrost cycles, which reduces performance and probably also equipment life.