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IIR document

Gascooler optimal pressure revisited.

Number: 0170

Author(s) : HEERUP C.

Summary

The quest for finding the optimal relation between the power consumed by the compressor and the performance of the heat exchanger rejecting the heat, either to the ambient or utilised for heating purposes has been the subject for many studies not least when CO2 is used as the working fluid.
The practical embodiment in commercially available control systems is usually incorporating a curve to minimise the compressor load for a given set of operating conditions approximating the optimal relation between the pressure and the temperature at the outlet of the heat exchanger regardless of if it is cooling or condensing CO2 gas.
However, this curve comes short of optimising heat pump or heat recovery operation when a given temperature is needed for supply to, and under varying temperatures returned from, a heating system. This is analysed as an first approach by a simple model for off-design operation conditions for a given heat exchanger. As a second approach a manufacturer calculation software for plate heat exchangers is used.
For a large range of operating conditions, we found that the optimal pressure seems to be considerably higher than the pressure resulting from the commercial controls systems. This is also the case for an air-cooled heat exchanger rejecting the heat to the ambient modelled in a freeware from NIST and this was a surprise as it was believed that the controls were developed for these applications.
Results are presented that indicate the potential improvement in both efficiency and capacity ranging from app. 5% to 20% for subcritical to trans critical operating conditions. For the air-cooled gascooler the highest potential for improvement seems to be for operation in vicinity to the critical point.

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Pages: 9 p.

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Details

  • Original title: Gascooler optimal pressure revisited.
  • Record ID : 30029762
  • Languages: English
  • Subject: Technology
  • Source: 15th IIR-Gustav Lorentzen Conference on Natural Refrigerants (GL2022). Proceedings. Trondheim, Norway, June 13-15th 2022.
  • Publication date: 2022/06/13
  • DOI: http://dx.doi.org/10.18462/iir.gl2022.0170
  • Document available for consultation in the library of the IIR headquarters only.

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