Improving heat pump performance via compressor capacity control : analysis and test

Prepared in association with Heat Transfer Laboratory, Dept. of Mechanical Engineering, Massachusetts Institute of TechnologyThe heat pump has long been of interest as a heating device because of its ability to deliver more heat energy than it consumes. The present work outlines past, present, and future developments in heat pump technology and indicates key areas of improvement. One method of improvement, the capacity controlled heat pump, has been studied in detail. An analysis of conventional and capacity controlled air-to-air heat pumps has been performed, using detailed computer simulations. New system sizing guidelines are outlined for capacity controlled units, resulting in as much as a 30% per year energy savings over conventional heat pumps in two of the six locations studied. Economic studies, comparing conventional and capacity controlled heat pumps to gas and electrical resistance heat, with and without air conditioning, indicate that capacity controlled heat pumps could soon be superior to gas heating in some locations, depending on energy prices. All of the economic studies have been done for a range of gas and electricity prices, and include amortization of capital costs as well as operating costs. Finally, preliminary development work on a new, potentially efficient and inexpensive, continuously variable compressor capacity control device is described. Test results on components of the early suction-valve cut-off control mechanism indicate that it is possible to design a controllable device to function in high speed (3600 RPM) compressors. However, more development work is needed