30 May 2005
The COP of a heat pump depends on compressor efficiency and the condensing and evaporating
temperatures. The COP of a heat pump system also depends on the drive powers to pumps and fans. For a
given situation, there will be an optimum balance between heat transfer and drive power. The optimum
can be found by considering flow related changes in drive power to the compressor, pumps, and fans.
This necessitates individual optimization of flows in the heat pump and heating system. Minimizing
pressure drops and selecting efficient pumps, fans and motors can improve the optimum. Motors must be
suitable for variable speed drive in applications where such control is appropriate.
A case study of a residential heat pump installation underlines the importance of load-matching,
optimized flow rates and efficient pumps, fans, motors and drives. Improvements in these aspects may
reduce total drive energy by 20-40 % in small systems. Also, variable speed drives for pumps can render
superfluous control valves and hence further contribute to reductions in pressure drop and pumping