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Progress in Ground-source Heat Pumps Using Natural Refrigerants
Wei Wu1, Harrison M Skye1, Lingnan Lin1
1National Institute of Standards and Technology, Engineering Laboratory, Energy and Environment Division, HVAC&R Equipment Performance Group, USA.
Abstract:
Natural refrigerants are attractive candidates for replacing the high Global-Warming- Potential fluorinated refrigerants used in ground-source heat pumps (GSHPs). This paper presents a comprehensive survey on GSHPs using CO2, NH3, water, and hydrocarbons. We compared the refrigerants' thermodynamic properties, analyzed their performance in brine-to-air and brine-to-water GSHPs, and discussed recent progress in their use in GSHPs. Studies of CO2 were the most common due to its favorable properties, covering advanced cycles, direct-expansion, secondary fluid, and hybrid GSHPs. Though with toxicity concerns, NH3 was the second most studied, including vapor-compression GSHPs for heating, absorption-type GSHPs to eliminate ground imbalance, and hybrid compression-absorption GSHPs to widen the operating temperature range. A few studies evaluated water as a refrigerant for absorption-type GSHPs, including applications for solar cooling, ground imbalance, and district heating. Propane was the only hydrocarbon considered for GSHPs, including analyses on refrigerant charge, performance analysis, and propane as a secondary fluid.
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