Current status and new developments on high temperature heat pumps.

Abstract

This review highlights the current status and new developments on high-­temperature heat pumps with heat supply temperatures above 90°C. Besides the vapor compression heat pumps, the focus of this work is on absorption heat pumps, absorption heat transformers and compression-­resorption heat pumps. Moreover, recent advancements in compressor technologies and working fluids for high-­temperature vapor compression heat pumps are also highlighted. A few manufacturers are available in the high-­temperature heat pump market segment that can supply single-­stage water/LiBr absorption heat transformer and ammonia/water compression-­resorption heat pump technologies. The heating capacity range of the commercial LiBr heat transformers is from 150 to 10,000 kW, while the thermal COP is between 0.45 and 0.50 at the temperature lift of up to 50 K. The commercially available compression-­resorption technology delivers heat up to 120°C, while the obtained electrical COPs are about 6.1 (at 22 K lift), 4.3 (at 65 K lift) and 2.4 (at 75 K lift). Many theoretical and experimental studies have been carried out in order to extend the limit of achievable temperature lift and COP of high-­temperature heat pumps.