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Investigation on the use of subcooling control in reversible residential air-conditioning systems.

Number: 0401

Author(s) : CARVALHO B.Y. K. de, HRNJAK P. S.

Summary

Subcooling control using an electronic expansion valve (EXV) is a promising alternative to evaporator superheat-based refrigerant throttling to improve performance without increasing system complexity. The implementation involves using an EXV to control subcooling and maximize performance while the accumulator acts as a low-pressure receiver storing the excess refrigerant and keeping excess liquid from reaching the compressor. Two off-the-shelf R410A 7kW reversible systems were modified to allow subcooling control in both A/C and H/P. The high-efficiency system used a variable speed compressor, thermostatic valve for cooling and EXV for heating. While the low-efficiency system used a single speed compressor, orifice-piston tubes, and heat exchangers with 1/5 the surface area of the high-efficiency system. Experimental results showed improvements in COP of up to 4.7% and cooling capacity of up to 6.3%. In heat pump operation the HPF also increased by up to 6.2% and heating capacity by up to 9.0%. The low-efficiency system showed greater improvements in A/C while the high-efficiency system showed better results in H/P. The load followed by condenser geometry have the strongest influence on subcooling control performance improvement. A control curve for the COP-maximizing subcooling based on the temperature difference between condenser saturation and air inlet showed good agreement with both systems. On the other hand, due to heat exchanger size differences the control scheme must be defined separately between cooling and heating modes. The accumulator’s ability to hold saturated liquid was evaluated by visualization and modelling. The experimental results indicated liquid entrainment as the liquid level on the accumulator increased when subcooling was lowered. The accumulator must be properly designed as a low-pressure charge receiver to allow stable and reliable operation with subcooling control.

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Details

  • Original title: Investigation on the use of subcooling control in reversible residential air-conditioning systems.
  • Record ID : 30031508
  • Languages: English
  • Subject: Technology
  • Source: Proceedings of the 26th IIR International Congress of Refrigeration: Paris , France, August 21-25, 2023.
  • Publication date: 2023/08/21
  • DOI: http://dx.doi.org/10.18462/iir.icr.2023.0401

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