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We are assessing high-efficiency electric heat pump water heating systems that use supercritical carbon dioxide as a refrigerant. CO2 heat pump water heaters (HPWHs) were first commercialized in Japan in 2001. Among heat pump water heaters, systems using a CO2 (or R744) refrigerant achieve a coefficient of performance (COP) greater than 3.2 compared to 2-2.5 for standard refrigerants. CO2 HPWHs have a broader range of operating temperatures, allowing the to maintain capacity at low temperatures, with a COP of around 2.0 at 17 degrees F. R744 also has a global warming potential of 1 compared to about 2,000 for typically used refrigerants (like R410).

Current Stage: Emerging Technology Assessment
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