Development of a compression-absorption heat pump system for utilizing low-temperature geothermal water

Abstract

Heat pump is an effective way to use the low temperature geothermal water with temperature lower than 50℃ for building heating. Compared to the conventional vapour compression heat pump, the compression-absorption heat pump (CAHP) can obtain higher heat sink temperature with lower compression ratio. Besides, the temperature glide in the generator and absorber of CAHP can be fitted to the heat source and heat sink, which achieves better coefficient of performance. Two models, respectively, for the generator and whole system using ammonia-water (NH3-water) as the working fluid are proposed, and the effects of different concentration of strong solution, cycle ratios, heat source temperature and spray density on the generator are investigated. The objective is to analyse the performance of CAHP system driven by low temperature geothermal water. The results show that the maximum of overall heat transfer coefficient of the vertical out-tube falling film generator can be obtained with the optimum spray density of around 0.16 kg/ms and there is an optimum concentration of around 65% for the CAHP system. When the low heat source temperature between 30℃ and 40℃, the high heat sink temperature can reach to 65-70℃.