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Liquid chiller using carbon dioxide in a transcritical process.

Author(s) : REKSTAD H., SKIPLE T., SKAUGEN G., et al.

Summary

A 40 kW cooling capacity liquid chiller using carbon dioxide (CO2) has been designed, built and tested experimentally. The prototype had the possibility to reject heat both to air and water. Both the water chiller and the gas coolers are new designs adapted for CO2. The water cooled gas cooler was a compact multi tube-in-tube counter flow concept, whereas the air cooled gas cooler was a conventional round tube in fin. The liquid chiller/evaporator was based on a tube-in-shell concept. The compressor was a semi-hermetic piston type. Experiments were conducted with varying cooling water temperatures and at steady state conditions. Measured cooling capacity at steady state conditions showed a cooling capacity of 16 to 34 kW, depending of high pressure and cooling water temperature and flow. The COP varied with high pressure, cooling water temperature and flow. Optimum high side pressure was 70 bars for cooling water temperatures below 18°C, whereas 80 bar above. The heat rejector worked well as a gas cooler and relatively good as a condenser with sufficient cooling water flow. Measured evaporator overall heat transfer coefficient (U-value) was lower than expected due too lower refrigerant charge than optimum. Additional experiments to find optimum evaporator refrigerant charge showed that increasing the refrigerant liquid height from 37 to 55% of full, increased the evaporator U-value from 800 to 1500 W/m2.K. Preliminary tests also show that an additional option is to combine chilling with up to 80°C hot water production. This initial study shows that the CO2 liquid chiller technology is promising. However, there is still room for performance improvements.

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Pages: 2008-2

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Details

  • Original title: Liquid chiller using carbon dioxide in a transcritical process.
  • Record ID : 2009-0136
  • Languages: English
  • Source: 8th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2008)
  • Publication date: 2008/09/07

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