Advances in vapor compression air source heat pump system in cold regions: A review

Vapor compression air source heat pump (VCASHP) system has been widely applied due to its simple structure and low initial cost. However, there are a series of problems when the system is operated for space or water heating in cold regions, and a number of research groups have done much work to improve VCASHP systems for solving these problems over the last two decades. This review presents an update on the recent advances in VCASHP systems applied in cold regions. In this paper, the advanced systems are classified into three major types: single-stage, dual-stage and multi-stage compression systems. In addition, the dual-stage compression system is divided according to the number of compressors and separate loops into quasi-two-stage, two-stage and cascade compression systems. The heating performances and characteristics of each type of compression systems with different working fluids and intermediate configurations have been analyzed and summarized. Meanwhile, several issues of these advanced systems that impede their widespread applications in cold regions are proposed. It is hoped that both the reviewed contents and proposed issues may be useful to the research fellows working in this field.