Cold climate air source heat pumps: Industry progress and thermodynamic analysis of market-available residential units

Air source heat pumps are an excellent electric alternative to fossil fuel based heating systems for reducing residential greenhouse gas emissions, but common mild climate systems suffer significant performance losses at the low outdoor air temperatures experienced in regions with cold climates. Improved heat pumps for cold climates are available on the market, but they are more expensive and their adoption to date has been relatively low, suggesting that there is work yet to be done in this field. This paper presents an analysis of market-available air source heat pumps identifying and discussing the cold climate technologies found in residential centrally-ducted cold climate systems. It shows that all of these heat pumps use rotary or scroll type variable-speed compressors, accumulators, and reverse cycle defrosting, and that a small number also include refrigerant injection and/or specialized refrigerant charge management devices. Available performance data for these heat pumps reveal that most of these systems still exhibit a significant loss of heating capacity at cold temperatures and are unlikely to meet the entire heating needs of a home in regions where temperatures drop below −15°C, necessitating the use of auxiliary heating systems. A review of the literature on cold climate heat pumps is also included to highlight additional design concepts and innovations that have not yet been implemented by the industry, but might further improve the performance and uptake of heat pumps in cold climates.