A study on the performance of multi-stage condensation heat pumps

Abstract

In this study, computer simulation programs were developed for multi-stage condensation heat pumps and their performance was examined for CFC11, HCFC123, HCFC141b under the same condition. The results showed that the coefficient of performance (COP) of an optimized ‘non-split type’ three-stage condensation heat pump was 25–42% higher than that of a conventional single-stage heat pump. The increase in COP differed among the fluids examined. The improvement in COP was due largely to the decrease in average temperature difference between the refrigerant and water in the condensers, which resulted in a decrease in thermodynamic irreversibility. For the three-stage heat pump, the highest COP was achieved when the total condenser area was evenly distributed to the three condensers. For the two-stage heat pump, however, the optimum distribution of total condenser area varied with working fluids. For the three-stage system, splitting the condenser cooling water for the use of intermediate and high pressure subcoolers helped increase the COP further. When the individual cooling water for the intermediate and high pressure subcoolers was roughly 10% of the total condenser cooling water, the optimum COP was achieved showing an additional 11% increase in COP as compared to that of the ‘non-split type’ for the three-stage heat pump system.