R410A/R134a双级耦合热泵系统最优中间水温实验研究

Experimental Investigation on the Optimal Intermediate Water Temperature in a R410A/R134a Cascade Heat Pump System

在低温工况下,双级耦合热泵系统可克服常规空气源热泵系统运行时制热量下降、系统性能系数(COP)降低等系统性能恶化的问题。当系统的其他参数不变时,耦合系统性能受中间水箱水温的影响。基于双级耦合热泵系统的简单分析,以R410A和R134a的双级耦合热泵机组为实验平台,在高温级冷凝温度50～75℃、低温级蒸发温度-30～-10℃及中间水温15～35℃的各种工况下,对影响最优中间水温的主要因素进行了实验研究。实验结果表明:当其他参数不变、中间水温发生变化时,系统COP呈现先增大后减小的趋势,系统最大COP值对应的最优中间水温始终是存在的。结合实验数据,可以发现:最优中间水温随低温级蒸发温度、高温级冷凝温度的上升而升高,其中低温级蒸发温度对最优中间水温的影响更大。在改变外部因素环境温度和供水温度的工况下,通过大量实验数据,拟合得到以蒸发温度和冷凝温度为自变量的最优中间水温的函数关联式,对优化R410A/R134a双级耦合热泵系统的实际运行具有一定指导作用。

The cascade heat pump system can overcome such problems as the deteriorated heating capacity and low coefficient of performance（COP）in conventional air source heat pump system under low temperature conditions.However,when other parameters of the cascade system are constant,its performance will be affected by the intermediate water temperature.Based on the simple operation analysis of the cascade heat pump system,an R410 A/R134 acascade heat pump platform was designed and tested under various conditions when the condensing temperature,evaporating temperature and intermediate water temperature were ranged within 50-75℃,^-30--10℃ and 15^-35℃,respectively,in order to reveal the main factors influencing the optimal intermediate water temperature. The experimental results show that when keeping other parameters constant,the coefficient of performance increases firstly and then drops with theintermediate water temperature,and that there always exists an optimal intermediate water temperature corresponding to the maximum COP value.According to the experimental data,it can be found that the optimal intermediate water temperature increases with the evaporating temperature in low-temperature cycle,and the condensing temperature in high-temperature cycle and is more affected by the evaporating temperature.By changing external factors such as the ambient temperature and water temperature,a function correlation of the optimal intermediate water temperature with evaporating temperature and condensing temperature as the independent variables is obtained by fitting a large number of experimental data,which could provide a guidance to the optimization on actual operation of the R410 A/R134 acascade heat pump system.