Feasibility and performance analysis of a hybrid GAX-based absorption-compression heat pump system for space heating in extremely cold climate conditions

Abstract

Absorption heat pumps (AHPs) can be thermally activated by low-grade heat sources for space heating. The efficiency can be greatly improved by adopting GAX-based internal heat recovery, which lifts the heat source temperature demand and deteriorates the cold climate condition adaptability, and thus immensely limits the widespread application. In this paper, a hybrid GAX-based absorption-compression heat pump (ACHP) system is proposed to expand the geographical scope of application in extremely cold climate conditions, to lift the heat supply temperature, and more importantly to utilize heat sources of lower temperatures. A mathematical model was developed and validated in comparison with experimental and theoretical results from the literature. Feasible generation-evaporation temperature (Tg-Te) conditions to enable GAX were presented in detail. Coefficient of performance (COP), primary energy ratio (PER), heat supply temperature, heating capacity, and heat duty of main components were investigated concerning different working conditions. The possible sensible and latent heat recovery ratio of the GAX was explored. The results show that when Pr increases, the feasible Tg-Te area moves towards the lower Tg and Te sides. The system can be utilized for building floor heating with PER above 1.116, COP higher than 1.614, temperature lift (ΔTlift) up to 81.85 °C even when ambient air temperature (Tamb) is down to −40.6 °C, and for fan coil heating when Tamb is above −40.0 °C with PER above 1.074, COP over 1.615 and ΔTlift up to 85.92 °C. The system can utilize heat sources down to 80 °C by adjusting the working pressure ratio (Pr), highlighting the possibility of integration with solar collectors for heating purposes.