Wide variety of CO2 heat pump applications presented at Gustav Lorentzen

By Janaina Topley Lira, Jul 10, 2012, 16:51 3 minute reading

CO2 heat pumps were widely discussed in a variety of applications at the 10th Gustav Lorentzen Conference on Natural Refrigerants, organised 25-27 June, in Delft. R744.com reports on a research into a transcritical heat pump for industrial waste heat recovery, an R744 reversible heating and cooling system for electric vehicles, and CO2 commercial heat pump water heater efficiencies.

Low grade industrial waste heat recovery with CO2 transcritical heat pumps in cold climates, V. Minea
 
The paper presented discusses a number of key operating parameters and energy performances achieved by a 7kW transcritical CO2 heat pump prototype. With the aim of recovering some of the low grade heat losses from the Canadian manufacturing industry, which represent 24% of total losses, the CO2 heat pump prototype was designed to recover heat from industrial low-grade effluents entering the system at the following temperatures:
 
  • Winter conditions: 7°C, 10°C, and 12°C
  • Summer conditions: 7°C and 15°C
 
The CO2 water to water transcritical heat pump includes a 7 kW, high-pressure, semi-hermetic, single stage, constant-speed compressor, three plate heat exchangers, a low pressure side receiver and an electronic expansion valve. In the winter hot water was produced at 67°C, 69°C, and 71°C from cold water entering the heat pump at 7°C and in the summer hot water was produced at 72°C and 77°C from cold water entering the heat pump at 17°C. However, relatively low thermal effectiveness of the internal heat exchanger was achieved (41.4% in the winter and 17.5% in summer “extreme” operating conditions), therefore further design improvements are required.
 
Investigation of a reversible cooling heating system for electric vehicles under frosting conditions using CO2 as working fluid, A. Steiner and R. Rieberer
 
In electric vehicles little waste heat is available to heat the car during the cold season, therefore a heat pump presents an attractive solution for heating the passenger compartment without reducing the cruising range, unlike PTC elements. Steiner and Rieberer’s paper looked a reversible heat pump for an electric car using CO2 under frosting conditions because frost formation on the exterior heat exchanger typically reduces performance and system efficiency.
 
The test revealed that at ambient temperatures around 0°C and 75% relative humidity, frost formation on the exterior heat exchanger (EXH) decreases COP from approximately 3 to 2 after 30 minutes, and the heating capacity changed from 1.7 to 1.2 kW, after which the EHX became partially blocked. To avoid this a fast and effective defrosting method is needed.
 
In addition to testing, frost formation was modelled in Modelica, giving good results when modified to take into account the rising air-side pressure drop.
 
Next generation commercial heat pump water heater using carbon dioxide using different improvement approaches, C. Bowers, M. Peterson, S. Elbel, P. Hrnjak
 
In this paper performance results from two R744 commercial heat pump water heater systems, a baseline system and one with an internal heat exchanger, both of approximately 35 kW and a baseline unit using R134a of the same capacity and footprint are compared. The study investigated the effect of water temperature lift on system performance by changing water flow rate and compared system efficiency for water outlet temperatures of 60°C and above.
 
According to results, as the water outlets temperature is increased to 80°C the R744 internal hear exchanger system has a higher COP than the R134a system. It is predicted that the baseline R744 systems would provide 2% savings n energy use, while the R744 system with the heat exchanger has the potential to save up to 10% in energy usage at the higher water temperatures needed for sanitary applications in restaurant kitchens and laundry facilities.

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By Janaina Topley Lira

Jul 10, 2012, 16:51




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