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Preventing transcritical operation of CO2 refrigeration systems with ground coupling.

Number: pap. 187

Author(s) : LEIPER A., SKELTON J., RIVERS N., et al.

Summary

The comparatively low critical point (31.1°C) of CO2 (R744) when compared with more conventional refrigerants can make CO2 refrigeration systems inefficient. Above this point, the discharge CO2 refrigerant does not condense and the system operates transcritically. With no condensation and none of the latent heat associated with the phase change, systems must rely on sensible heat rejection. As such, systems operating transcritically have a lower capacity to reject heat and can be less efficient. In climates where ambient temperatures surpass 20-23°C, transcritical operation is often unavoidable and CO2 systems are not seeing the same successes as in colder climes. Maintaining subcritical operation when ambient temperatures are above the transcritical threshold requires an additional cooling medium other than air. One such alternative cooling medium can be provided by coupling the high pressure side of the CO2 refrigeration system to the ground with an aqueous loop. The fluid in this loop is circulated through a network of subsurface borehole heat exchangers and then to heat pumps to supply space heating and domestic hot water and subsequently a plate heat exchanger installed in the heat rejection side of the refrigeration cycle. Since ground temperatures are typically lower than ambient temperatures during the summer, subcritical cycle operation can be realised more often and vast improvements to coefficient of performance can be achieved. This paper presents data collected at two supermarkets, the first utilising ground coupling and the second using a typical air cooled refrigeration cycle. The paper describes the effect of the technology on the operation of a CO2 refrigeration system and results show that geo-coupling lowers condensing temperatures, providing a reduction in energy consumption of around 25% and helping to prevent transcritical operation. This improves pack reliability and opens up opportunities for CO2 in warmer climes.

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Pages: 8 p.

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Details

  • Original title: Preventing transcritical operation of CO2 refrigeration systems with ground coupling.
  • Record ID : 30012110
  • Languages: English
  • Source: 3rd IIR International Conference on Sustainability and the Cold Chain. Proceedings: London, UK, June 23-25, 2014
  • Publication date: 2014/06/23

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