Thermodynamic analysis and optimization of a balanced-type single-stage NH3-H2O absorption-resorption heat pump cycle for residential heating application

Abstract

Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology in efficient utilization of low-temperature heat for residential heating application. This paper proposes a balanced-type single-stage ARHP cycle based on the unbalanced ARHP cycle by eliminating the rectifier and depending on only one solution circulation pump. The proposed cycle can achieve internal mass and species conservation by changing the ammonia-water solution concentration difference at different pressure levels. A mathematical model is developed to obtain feasible high pressure/low pressure (PH/PL) pairs to enable the cycle. The cycle's coefficient of performance (COP) at different PH/PL pair values is investigated. The maximum COP is 1.51 and the corresponding heat supply temperature reaches 43.4 °C when PH/PL pair value is 1.50/0.48 MPa and heat source temperature is 95 °C. The maximum heat supply temperature can reach 53.4 °C and the minimum ambient air temperature to effect the cycle is −5.8 °C. Other parameters like heat output/inputs, solution circulation ratios, and absorption and desorption concentration gradients in the absorbers and generators are studied. Inner pressure (difference), COP and heat source temperature demand have been compared with those of the conventional absorption heat pump (AHP) cycle and the unbalanced ARHP cycle. The results revealed that the proposed cycle could work at lower heat source temperature (above 82 °C) and within wider heat source temperature range than the conventional AHP cycle, indicating that the proposed cycle is potential in efficient utilization of commonly used solar collectors for space heating. In addition, the proposed cycle could be operated at higher COP values and lower inner pressure differences than the unbalanced ARHP cycle.