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Experimental Evaluation of a Water Source CO2 Heat Pump Incorporating Novel Gas-Cooler Configuration

[+] Author Affiliations
Portia Murray, Stephen Harrison, Gary Johnson

Queen’s University, Kingston, ON, Canada

Ben Stinson

QSBR Innovations Inc., Kingston, ON, Canada

Paper No. ES2014-6668, pp. V002T12A004; 10 pages
  • ASME 2014 8th International Conference on Energy Sustainability collocated with the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology
  • Volume 2: Economic, Environmental, and Policy Aspects of Alternate Energy; Fuels and Infrastructure, Biofuels and Energy Storage; High Performance Buildings; Solar Buildings, Including Solar Climate Control/Heating/Cooling; Sustainable Cities and Communities, Including Transportation; Thermofluid Analysis of Energy Systems, Including Exergy and Thermoeconomics
  • Boston, Massachusetts, USA, June 30–July 2, 2014
  • Conference Sponsors: Advanced Energy Systems Division
  • ISBN: 978-0-7918-4587-5
  • Copyright © 2014 by ASME


Carbon dioxide’s use as an alternative refrigerant has been increasing in popularity due to its low global warming and ozone depletion potentials. In recent years, a number of companies and researchers have investigated applications of CO2 heat pumps for water heating.

This study investigates the experimental testing of a CO2 heat pump water heater (HPWH) at Queen’s University. For the tests, the conventional factory gas-cooler on an Eco-cute unit and air-source evaporator was replaced with a specially designed brazed-plate gas-cooler. It rejected heat to a 273 litre hot water and the evaporator sourced heat from a warm water supply.

Experiments were conducted using both forced and natural convection (i.e., thermosyphon) flow between the gas-cooler and hot water tank. Thermosyphon flow was studied to evaluate its effects on storage tank stratification and heat pump operation (i.e., coefficient of performance). Results were compared to forced circulation cases run over a range of flow rates.

In the forced convection flow test, it was observed that a decrease in gas-cooler average water temperature increased the coefficient of performance (COP) non-linearly and an increase in the water-side flow rate increased the COP and the effectiveness of the gas-cooler.

The thermosyphon had an average flow rate of 0.75 L/min and an average COP of 3.1. Thermosyphon flow kept the hot water tank fully stratified until fully charged. Water was delivered at an average of 70°C. It was also observed that thermosyphon flow rate depended on the state of charge (i.e., temperature distribution) in the storage tank.

In order to increase the performance, a gas-cooler with a lower pressure drop should be used to increase the thermosyphon flow rate.

Copyright © 2014 by ASME



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