An absorption-resorption heat pump cycle with internal heat recovery for space heating

Ammonia-water absorption-resorption heat pump (ARHP) technology is promising for development of efficient utilization of low-temperature thermal for space heating. This paper proposes a single-stage ARHP cycle by replacing the condenser and evaporator in a conventional absorption heat pump (AHP) cycle with a high-pressure absorber and a low-pressure generator, respectively. The proposed cycle can work depending on inner ammonia-water solution concentration difference under different pressure levels. A mathematical model was developed to investigate the feasible high-pressure/low-pressure (PH/PL) to effect the thermodynamic cycle. The cycle’s coefficient of performance (COP) can be optimized by the coupling adjustment of inner operation pressure difference and solution concentration difference. The cycle’s COP values under different PH/PL values are studied. Under given working conditions, the maximum COP can reach 1.55 and the corresponding optimum PH/PL value to effect the cycle is 1.40 MPa/0.38 MPa when the driving heat source temperature is 95°C. Heat supply temperature of 41.9°C and a corresponding COP value of 1.54 can be achieved When PH/PL value is 1.40/0.40 MPa and ambient air temperature is 5°C, which can basically meet the temperature demand of building floor heating. Furthermore, effects of ambient air temperature and driving heat source temperature on COP values are investigated. It is concluded that the proposed cycle can work when ambient temperature is above -7.5°C and the driving heat source temperature is over 85°C. Compared to the conventional AHP cycle, the driving heat source temperature range to effect the proposed cycle is much wider, indicating potential of integrating the proposed cycle with commonly used stationary solar collectors for winter space heating purpose.