Fang C. Chen

CFD SOLUTION AND EXPERIMENTAL TESTING OF BUOYANCY-DRIVEN CONVECTION CAUSED BY CONDENSERS IMMERSED IN A WATER TANK OF HPWH

Heat pump water heaters can cut electricity consumption, comparing with the conventional electric resistant water heating tanks by half. A conventional heat pump water heater (HPWH) requires a water circulating pump to sample water temperature every 15 minutes in the tank and to draw water to a condenser-water heat exchanger outside the tank, if water temperature is below the set point. The pump would be on at least once every 15 minutes, 24 hours a day. The novel design presented in this study was to insert the condenser coil through the opening on the top of the water tank. This design eliminated the need of the water circulating pumps, and thus greatly improved the reliability of the HPWH systems. Two types of condenser coil designs were considered; one was a bayonet tube (tube-in-tube) and one was the “U” tube. Previous test data indicated that “U” tube design performed better than the bayonet tube condenser coil, and thus only “U” tube condenser coil was considered in the study. With straight “U” tubes inserted into the tank, it was found that the convective heat transfer was not strong enough to break water temperature stratification in the tank, which resulted in a temperature differential of 16°C (30°F) from top to bottom. However, when the coil was built in “L” shape, the water stratification disappeared. A computational fluid dynamics code, CFD, was used to study the straight and L shaped condenser coils. Results from CFD simulation were compared with the experimental data and found they were close to each other.Copyright

Investigation of R417A as a Drop-In Alternative for R22 in a Residential Heat Pump

Heat pumps are efficient units for providing heating and cooling in both residential and commercial buildings. R22, however, is still being widely used in most heat pumps produced in the United States, which has been scheduled to phase-out by the end of the year 2020. At present, the majority alternatives of R22 consist of hydrofluorocarbon (HFC) refrigerants only. Unfortunately, these HFC replacements require synthetic oil and expensive modification. Recently, R417a, a new alternative of R22, is presented and does not require synthetic oil because R417a contains 3.4 % of R600 (butane). R600 is an excellent oil carrier. The emphasis of this paper is an attempt to document the findings of thermodynamic cycle, heat transfer, and experimental study on R417a serving as a drop-in working fluid in a two-ton split heat pump system.