Experimental investigation on a GAX based absorption heat pump driven by hybrid liquefied petroleum gas and solar energy

In this study, we presented a detailed experimental investigation of an air source liquefied petroleum gas (LPG)-solar driven absorption heat pump (LSAHP) using Generator Absorber heat eXchanger (GAX). The GAX absorption heat pump with a nominal heating capacity of 55 kW uses ammonia-water as working pairs and is powered by hybrid energy sources: a 45 m2 parabolic trough solar collector (PTC) and a direct-fired liquefied petrol gas (LPG) burner. The thermal performance of the PTC was characterized with selected on-sun conditions. Results showed that solar thermal efficiency can reach up to 53.55% with direct normal insolation of 450 W/m2 and inlet thermal oil temperature of 191 °C. Three operation modes were identified based on the driven energy sources: (i) LPG-Solar hybrid mode, (ii) Solar only mode, and (iii) LPG only mode. Under the average ambient temperature of 17.52 °C, 20.0 °C, 8.77 °C the averaged COPs of three modes are 1.54 (mode i), 1.63 (mode ii) and 1.20 (mode iii) respectively. Solar energy contributions reached 40.2% and 55.10% in mode i and mode ii separately which demonstrated the feasibility of the coupling of PTC and GAX heat pump to reduce the dependence on fossil fuel. The impact of operation conditions (ambient temperature, inlet hot water temperature, and LP gas flow rate) on the heating capacity and system performance were investigated under steady-state conditions. Results indicated that higher ambient temperature, higher gas flow rate, and lower inlet hot water temperature benefit the heat pump performance, among which the influence of ambient temperature is the greatest. COP reaches 1.47 with 19 °C ambient temperature and 35 °C inlet hot water temperature. It's worth noting that COP' achieves 1.82 under the same condition if we exclude the heat loss of flue gas.