The Performance of Compression-absorption Heat Pump System Using Low-temperature Geothermal Tail Water

Abstract

In china the resources of low-temperature geothermal water between 20 to 40 ℃ are very rich, and there are also a lot of geothermal tail water and waste heat water, which are discharged with the similar temperature. In order to reduce the energy consumption of building district heating, heat pump is often used to recover low-temperature geothermal tail water. Among the heat pump technologies, the compression-absorption heat pump (CAHP) has been recognized for a long time. Comparing with the compression heat pump, CAHP can get a high heat sink temperature with a lower compression ratio, and the temperature glide of the generator and absorber in CAHP can be fitted to the heat source and heat sink, which lead to a higher COP. The performance of a CAHP system using the ammonia-water mixture is analyzed in this paper. A model based on mass and energy balances in all components is developed, and a model of the vertical out-tube falling film generator is conducted especially. The results show that there is an optimum concentration around 65% for the system. The maximum of overall heat transfer coefficient can be obtained with the optimum spray density of around 0.16 kg•m-1•s-1. Based on a high heat sink temperature of 65℃ and a low heat source temperature from 30 to 40℃, the COP of the CAHP system is above 4.