Performance characteristics of a two-stage CO2 heat pump water heater adopting a sub-cooler vapor injection cycle at various operating conditions

• Published in: Energy (Oxford) 2014-12, Vol.77, p.570-578
• Main Authors: Baek, Changhyun, Heo, Jaehyeok, Jung, Jongho, Cho, Honghyun, Kim, Yongchan
• Format: Article
• Language: English
• Subjects: Applied sciences; CO2 heat pump water heater; Devices using thermal energy; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Heat pumps; Heat transfer; Hot water temperature; Injection ratio; Theoretical studies. Data and constants. Metering; Vapor injection; Water heating performance
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2014.09.038

The objective of this study is to investigate the performance characteristics of an injection CO2 (carbon dioxide) HPWH (heat pump water heater) at various operating conditions. In the standard and standby heat loss test conditions, the performance of a two-stage CO2 HPWH adopting a SCVI (sub-cooler vapor injection HPWH) cycle was measured and analyzed by varying the compressor frequency, the water flow rate, and the injection ratio at various outdoor temperatures. In the standard tests at the outdoor temperature of −15 °C, the COP (coefficient of performance) of the optimized SCVI HPWH was 7.6% higher than that of the non-injection HPWH. During the standby loss tests at the water flow rate of 200 kg h−1, the COP of the optimized SCVI HPWH was 7.1% higher than that of the non-injection HPWH. •A CO2 heat pump water heater adopting a vapor injection cycle is considered.•The performance of the SCVI HPWH is analyzed in standard and standby loss tests.•The optimum water flow rate and injection ratio are determined.•The performance comparison between the SCVI HPWH and air heating HP is conducted.