30 May 2005

REVIEW OF AIR-SOURCE HEAT PUMPS FOR LOW TEMPERATURE CLIMATES


Air source heat pumps are widely used for heating because of the relatively low installation costs. A
major disadvantage is that the heat output and COP decrease for low outdoor temperatures, when most
heat is needed. This paper presents the results of an extended literature and patent review of air source
heat pump concepts for low temperature climates as experienced in the northern parts of the United States
(excluding Alaska) and the southern parts of Canada. The heat pump concepts can be characterized by
cycle improvements to lower the discharge temperature of the compressor and increase the COP and heat
output at low outdoor temperatures. The advantages and disadvantages of several concepts shown in
different papers are presented and the thermodynamic performances are compared by simulation. In
addition, results of an investigation of refrigerants suitable for low temperature climates are shown.