Research progress of heat pumps in China from perspective of literature clustering

Based on the analysis of more than 15 000 citation information using the bibliometric method, this paper clusters the research directions of heat pumps in China from 1994 to 2020, describes the main areas and overall development trends in a macroscopic view, and reviews the four most active areas at present: ground-source heat pump, air-source heat pump (ASHP)-frosting and defrosting, ASHP-heating and solar-assisted heat pump. Ground-source heat pumps focus on the study of heat exchangers and thermal imbalances. The ASHP is the most popular research direction in recent years. The research on frosting and defrosting has undergone a transition from frosting/defrosting mechanism, defrosting methods and heat storage defrosting to frost-free ASHP. Cascade vapor compression ASHP and refrigerant injection technology are the main efforts to improve the applicability of ASHP in cold and severe cold zones. It also points out that industrial heat pumps may be the focus of future heat pump research, and the industrialization of electric vehicle heat pumps and heat pump water heaters is in strong demand.