Optimum utilization of recovered heat of a gas engine heat pump used for water heating at low air temperature

• Engine waste heat recovery represents one of the main advantages of gas engine heat pump.
• Recovered engine heat is used either to evaporate the working fluid or to heat the supplied water.
• Higher primary energy ratio has been obtained when recovered engine heat is transferred to water.
• Outlet water temperature between 34 °C and 50 °C is obtained during the considered modes.
• Engine speed should be optimized to get the required capacity with highest primary energy ratio.

Engine waste heat recovery represents one of the main advantages of gas engine heat pump (GEHP) as compared to conventional heat pump. At lower air ambient temperature, engine waste heat can be used either to evaporate the refrigerant in the refrigerant circuit (mode-I) or to heat the supply water (mode-II). In this paper, the performance of a gas engine heat pump integrated with heat recovery subsystem for both modes are experimentally investigated. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of engine speed (1300:2200 rpm), ambient air temperature (−3.3:22 °C) and condenser water inlet temperature (27:48 °C). Performance characteristics of the gas engine heat pump were characterized by outlet water temperature, heating capacity and primary energy ratio. The results showed that the effect of condenser water inlet temperature on the system performance is more significant than the effects of ambient air temperature and engine speed. Maximum primary energy ratio has been estimated with a value of 1.83 when the recovered engine heat is transferred to water while it is limited to 1.25 as the recovered engine heat is transferred to refrigerant circuit.