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.