Abstract: This investigation overviews the results of an experimental study pertaining to flammable refrigerant alternatives in water-to-water
heat pumps for buidling and home applications. The system studied here used a secondary heat transfer loop to communicate with the indoor space.
This isolates the flammable refrigerant in the outdoor section of the unit and demonstrates one configuration that could be accepted in the United States.
In contrast to the fluid survey of the intial study by Payne (1999), the present study emphasizes the performance of R32/290, R22, R290, and R22-REF
(direct expansion case) in the cooling and heating modes. The vapor compression cycle used an internal heat exchanger added between the liquid and vapor lines. Fluid
performance as a function of thermophysical properties and heat transfer characteristics are addressed for each cycle configuration.
The heat pump charged with R32/290 had the closest performance to the R22 direct expansion system in the cooling mode. Furthermore, the internal heat
exchanger system performance exceeded that of the basic vapor compression cycle configuration. In the heating mode, R290 in the basic configuration
had the closest approximation to the R22 direct expansion performance. The application of the internal heat exchanger degraded R290's performance.
Keywords: water to water heat pump, zeotropic mixture, flammable refrigerant, R-32, R-290, R-22
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