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Energies 2017, 10(6), 810;

Experimental Study on the Performance of Water Source Trans-Critical CO2 Heat Pump Water Heater

State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China
Xi’an Jiaotong University Suzhou Academy, Suzhou 215123, China
Author to whom correspondence should be addressed.
Academic Editor: Tapas Mallick
Received: 12 March 2017 / Revised: 2 May 2017 / Accepted: 3 June 2017 / Published: 14 June 2017
(This article belongs to the Section Energy Fundamentals and Conversion)
Full-Text   |   PDF [2572 KB, uploaded 15 June 2017]   |  


The effect of the discharge pressure on the performance of the trans-critical CO2 heat pump with a low gas-cooler outlet temperature is experimentally investigated on a test rig of water source heat-pump water heater. The optimal discharge pressure of the trans-critical CO2 heat pump is investigated under different external operation conditions. When the tap-water temperature is low, the characteristic of the S-shape isotherm at the supercritical region has little effect on the occurrence of the optimal discharge pressure; while the mass flow rate of CO2, the suction pressure and the gas-cooler outlet temperature play a significant role in determining the emergence of the optimal discharge pressure. At the optimal discharge pressure, the COP reaches the peak; however, the corresponding heating capacity is still lower than its maximum, which is reached as the discharge pressure is slightly above the optimal discharge pressure. Reducing the tap-water flowrate or increasing the water-source temperature can increase the optimal discharge pressure. The COP is positively dependent on both the tap-water flowrate and the water-source temperature. In addition, the tap-water flowrate has a negligible influence on the maximum heating capacity while increasing the water-source temperature can greatly enhance the heating capacity. View Full-Text
Keywords: trans-critical CO2 cycle; heat pump; optimal discharge pressure; COP trans-critical CO2 cycle; heat pump; optimal discharge pressure; COP

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Liu, X.; Liu, C.; Zhang, Z.; Chen, L.; Hou, Y. Experimental Study on the Performance of Water Source Trans-Critical CO2 Heat Pump Water Heater. Energies 2017, 10, 810.

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