Development of a novel unbalanced ammonia-water absorption-resorption heat pump cycle for space heating

Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology for promoting efficient utilization of low-temperature thermal for space heating. This paper proposes a novel unbalanced ARHP cycle by replacing the condenser and evaporator in the conventional absorption heat pump (AHP) cycle with a high-pressure absorber and a low-pressure generator, respectively. The proposed cycle can work just depending on the concentration difference of ammonia-water solution under different pressure levels. A numerical model has been developed to investigate the feasible high-pressure/low-pressure (PH/PL) values to effect the thermodynamic cycle. The cycle's coefficient of performance (COP) under different PH/PL pair values and other given working conditions are studied. The maximum COP is 1.550 and the corresponding optimum PH/PL pair to effect the cycle is 1.40 MPa/0.38 MPa at a heat source temperature of 95 °C. When PH/PL pair value is 1.40/0.38 MPa, heat supply temperature of 44.5 °C and COP value of 1.331 can be obtained, which can basically meet the temperature demand of building floor heating. In addition, effects of different PH/PL pair values on solution circulation ratios and vapor discharge scopes of generators are discussed. It is concluded that the ideal PH/PL candidates yield large concentration difference between the inlet and outlet of generators and absorbers. Meanwhile, the solution circulation ratios of the two generators at ideal PH/PL pairs are acceptable values between 2.0 and 12.0. The cycle can work when the ambient temperature is above −7.5 °C and the driving heat source temperature is larger than 85 °C, which is potential in efficient utilization of commonly used stationary solar collectors for winter heating. •An unbalanced absorption-resorption heat pump cycle was developed.•Mathematical model was developed to explore feasible inner operation pressures.•Effects of different operation parameters on the cycle's COP were analyzed.•Performance was compared with that of conventional absorption heat pumps.•COP of the whole solar driven space heating system was investigated.