Study on a Combination System of Heat Pumps with Hot & Cold Water Recovery


In order to improve the performance of heat pump systems and save energy, a combination system consisting of three heat pump units was retrofitted to recover cold and hot water to simultaneously meet the requirements of air conditioning as well as hygiene hot water for a Physical Therapy Center. The basic principle of this combination system was that when two units of the system operated for refrigeration with hot water recovery and the other one operated for producing hot water with cold water recovery, it could produce enough chilled water for air conditioning and hot water for bath at the same time, and it could take utmost advantage of heat pump and improve its overall efficiency. The typical performance of the combination system in summer was theoretically analyzed based on the properties of R407C and the characteristics of operation modes with various methods of heat recovery. It showed that the retrofitted system could obviously increase the outputs of cooling and heating. For example, the maximum outputs of cooling and heating would increase 84.5% and 288.4%, respectively, so that it could shorten the operation hour and save more energy than the original system without heat recovery. The results showed that the electricity-saving rate of the retrofitted combination system varied in the range of 26.7%∼41.9%. Meanwhile, a primary on-site measurement, which was carried out on the condition of that two of the three heat pumps operated as water chillers with hot water recovery, and the other one operated as water heater with cold water recovery, showed that the system could simultaneously produce 255.5kW cooling and 365kW heating, and its overall performance of coefficient (COP) reached 4.62. Furthermore, the thermal pollution to environment caused by the original system in summer could be efficiently reduced by heat recovery.

  • Abstract
  • Background
  • Introduction of the Combination System and Its Retrofit
  • Theoretical Analysis of the System Performance
  • 1. Operation modes
  • 2. Theoretical analysis of the cycles
  • On-Site Measurement and Analysis
  • Summary
  • Acknowledgments
  • Nomenclature
  • References

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