Foster-Miller conducted this project to investigate the use of HFC refrigerants in low temperature supermarket refrigeration systems to accelerate the replacement of CFC refrigerants and increase the peak demand savings. In cooperation with the Electric Power Research Institute (EPRI), two low temperature display case circuits at a Safeway in Menlo Park, CA were first converted from R-22 to R-502. The systems were then converted to the HFC refrigerants including removal and flushing of the conventional compressor oil. Two compressor configurations consisting of stand-alone and multiple parallel compressors were considered. Two liquid sub-cooling methods were also examined, consisting of mechanical sub-cooling and external liquid-suction heat exchangers. These two methods were used alternately with both compressor configurations. The testing at the site consisted of alternating between these system configurations while testing over a saturated discharge temperature range of 70 to 105ºF. This procedure produced data that allowed each of the HFC refrigerants, R-404a and R-507, to be compared to R-502, and provided a complete characterization of each compressor and system configuration. A comparison of the energy consumption and demand was then made.

Two sets of tests were conducted with the R-404a and R-507 to determine the importance of expansion valve and control adjustment on refrigerant conversions. In the first set, no adjustment was made to the expansion valves at the display cases, and in the second set of tests, the expansion valves were adjusted to produce 5ºF of superheat at the evaporator outlet. The discharge air temperature at the display cases was also adjusted by the system controller to the desired value.

The test results showed that refrigerant R-404A used slightly more energy and had slightly lower EER than R-502. This difference was decreased after the expansion valves at the display cases and the system controller were checked and adjusted. The importance of sub-cooling was also demonstrated, particularly the use of liquid-suction heat exchangers.  Performance could be further improved by maintaining the head pressure as low as possible. This had two effects: 1) maximize EER whenever low head pressure is maintained and 2) minimize the liquid temperature at the inlet of liquid-suction heat exchangers, which will produce the lowest liquid temperature at the exchanger outlet.

Test results for R-507 showed that this refrigerant had slightly better performance than R-502. Energy consumption and EER for R-507 were both improved when adjustments were made to the expansion valves and the system controls. The use of low head pressure was verified for this refrigerant as for R-404A.

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