Experimental investigation on a semi-open air cycle heat pump system equipped with booster turbo-expander.

• The prototype varies within 15 % in ambient temperature range of −30 ∼ 7℃. • The frosting has no impact on the overall efficiency of system. • It has the potential for application in the field of high temperature heating. • Utilizing high-efficiency compressors could improve the system's coefficient of performance by 13.47 ∼ 31.50 %. Different from conventional vapor compression heat pump system, this investigation presented a semi-open air cycle heat pump system, whose performance was experimentally assessed across diverse conditions. The prototype showcased stable heating performance with coefficient of performance surpassing 1.0 at ambient temperatures above −7°C and maintaining its variation within 15 % in the ambient temperature range of (−30 ∼ 7) °C. According to the analysis of the experimental results, although frosting has an impact on some parameters, the overall efficiency of the system remains stable over time. These special designs of high-pressure ratio and oil cooling of compressor could make the system temperature reaching 132 °C, indicating that the system has the potential for application in the field of high temperature heating. Heat exchanger analysis revealed an imbalance in heat exchange ratios between oil–water heat exchanger and air–water heat exchanger. The prototype achieved 58 ∼ 72 % of a significant conversion efficiency of electric energy to oil internal energy, proposing that utilizing high compression efficiency compressors could enhance system coefficient of performance by (13.47 ∼ 31.50)%. The isentropic efficiency and expansion work recovery efficiency of booster turbo-expander were calculated as (59 ∼ 65)% and (33 ∼ 40)% respectively. Additionally, it was found that frosting could optimize the recovery rate of expansion work under specific conditions. [ABSTRACT FROM AUTHOR]