Investigation of Two Performance Improvement Options For Household Refrigerators

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Due to environmental concerns, the refrigeration industry is facing the challenge of developing more efficient and environmental friendly refrigerators. Environmentally harmful refrigerants, CFC's and HCFC's, have already been shifted toward environmental friendly refrigerants such as HFC's and hydro carbons. However HFC's have a significant global warming potential. Accordingly, new policies have taken effect which are forcing the refrigerator industry to develop refrigerators that will reduce energy consumption and refrigerant emissions to reduce energy bills and the global warming effects of refrigerators.
This study presents the research conducted on the condenser improvement of one of the commercially available household refrigerators and designing and applying a so-called Alternating evaporator duty cycle (AED) with a two step capacity modulated compressor. In the condenser improvement study, a household refrigerator's condenser configuration was changed from the cross-flow configuration to the counter-flow configuration without changing other components and cabinet structure. Ten experiments for different refrigerant charges were conducted and it was experimentally proved that the refrigerator with counter flow condenser consumes 1% less energy compared to the one with cross-flow condenser. To study the potential of the AED cycle, a side-by-side household refrigerator equipped with a conventional cycle was converted into the AED cycle. First of all, the performance of the refrigerator with the new cycle was simulated and then cycle components were designed. Two different kinds of evaporators were used for food (R) cabinet such as forced convection fin-and-tube type evaporator (FCE) and natural convection tube-and-plate type evaporator (NCE), to investigate the humidity control improvement.
Experimental results shows that, average humidity ratios of freezer (F) and R compartments during the cyclic operations are 0.5 gH2O/(kg of dry air) and 2.5 gH2O/(kg of dry air), respectively using the FCE and 0.6 gH2O/(kg of dry air) and 2.4 gH2O/(kg of dry air), respectively with NCE. Therefore, the humidity ratio of R compartment is maintained at 4-5 times higher level than that of F compartment for the AED cycle, and also 4 - 5 times higher than that R and F compartments for the base cycle. In addition to the better humidity control, AED cycle provides separate and more efficient cabinet temperature control.