Establishment and Theoretical Analysis of a Solar Driven NH3-H2O Resorption Heat Pump Cycle
Abstract
The instability and intermittency feature of solar thermal made it difficult to develop heat pumps driven by high-temperature solar thermal. To make full utilization of low-temperature solar thermal, a novel balanced-type absorption-resorption heat pump cycle with a simple construction is proposed in this paper. The cycle is based on concentration difference of ammonia-strong, ammonia-weak and ammonia vapor (in fact a very small amount of water vapor inside). In this cycle, the solution absorbs vapor flows generated from a low-pressure and high-pressure generator in a corresponding low-pressure and high-pressure absorber which are cooled by return water flowing through. The strong solution out from the low-pressure generator and the weak solution out from the low-pressure is mixed together and then pressurized by a solution pump before sent to the high-pressure generator and absorber. In order to achieve the optimal operating conditions, an analytical model is developed and the feasibility and performance were investigated by modelling and simulation when factors like high and low generating pressure, high and low generating temperature, high-temperature absorbing temperature vary. The new cycle has a smaller operating pressure differential compared to the conventional single-effect heat pump cycle and is more suitable for the temperature characteristics of solar thermal due to its exemption from a rectifier. After optimization of the proposed cycle, the maximum coefficient of performance (COP) value of 1.42 can be obtained under certain given conditions. COP increases with the increasing of the high-pressure generating temperature (or temperature of solar thermal).