In retrofit unit, the COP increased by 32.2% with R600a, while energy use dropped 4.5%.
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Since the 1990s, when NGO Greenpeace introduced its GreenFreeze concept, isobutane (R600a) has been widely used in domestic refrigerators in many countries around the world, with a maximum charge of 150g (5.3oz).
In the U.S., progress has been slower, because the Environmental Protection Agency (EPA) didn’t increase the change limit for R600a in domestic refrigerators from 57g (2oz) to 150g until September 2018. But beginning last year, U.S. retailers began showing a range of full-size R600a refrigerator/freezers.
The wisdom of using R600a instead of a high-GWP HFC refrigerant has been recently demonstrated by Nigerian researchers in a study published in the Journal of Physics: Conference Series. The lead researcher was Solomon Banjo, engineer in the Mechanical Engineering Department, Covenant University, Ota, Nigeria.
The study, “Experimental analysis of the performance characteristic of an eco-friendly HC600a as a retrofitting refrigerant in a thermal system,” investigated the performance characteristics of a domestic refrigerator using 46g (1.6oz) of R600a as an alternative to 70g (2.5oz) of R134a.
Notably, the researchers used the same system to test both refrigerants, first R134a, and then, with some retrofitting, R600a, at an ambient temperature of 28°C (82°F). “Some components of the system were altered such as the compressor, mineral oil, capillary tube and dryer so as [to] accommodate the new configuration,” the study said.
The results of the study showed that the coefficient of performance (COP) of the system increased by 32.2% with R600a, including an energy reduction of 4.5%. In addition, the system with R600a attained an evaporating temperature of -21°C (-5.8°F) in 60 minutes (pull-down time), vs. 2 hours and 15 minutes with R134a.
During a five-hour test, the COP of the R600a system ranged from 7 to 8, while the COP of the R134a system varied from 5 to 6.5. During the last 150 minutes of the test, the power of the R600a system was 85W while the R134a system was 89W.
The study also found that the heat rejection of the condenser was 12.8% greater with R600a than with R134a.
“The energy conservation rate was improved with isobutane refrigerant (HC600a) and this serves as one of the parameters to justify isobutane as the best alternative refrigerant to [conven- tional] refrigerant (HFC134a),” the study concluded.