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Effect of heat exchanger size on subcooling control in residential air conditioning systems.

Number: 2282

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

Summary

With the increasing pressure on reducing the environmental impact of air conditioning and heat pump systems alternative solutions are required to maintain or increase energy efficiency while also decreasing the overall carbon footprint of such systems. This paper will focus on experimental and model evaluation of heat exchanger (HX) size effect on the control of subcooling in residential air conditioning systems.
Two separate systems are investigated: a high-efficiency system with large heat exchangers, variable-capacity compressor, and thermostatic valve; and a lower efficiency system with smaller heat exchangers, fixed speed compressor, and piston-orifice tube. Experimental results showed that both systems improved with subcooling control with relative increases in COP from +4.7% to +8.9% for the large-HX system and from +4.3 to +14.2% in the small-HX system. Subcooling control also increased capacity for both systems ranging from +5.3% to +15.6%. With a more significant overall improvement in performance for the small-HX system because its baseline used a fixed-expansion device which suffers a decrease in efficiency when operating outside of the rating condition. A system model was developed and predicted for a system using the same variable capacity compressor that the COP-maximizing subcooling is a function of both heat exchanger size and capacity, with the latter having a more pronounced effect on it. The system with heat exchangers 5 times smaller showed an increase in COP-maximizing subcooling of only 1-2 K for residential applications at the A rating condition. When the capacity was increased from 3 kW to 7 kW COP-maximizing subcooling rose from 2-3 K to 6-8 K for both small and large heat exchanger systems.
The control strategy proposed based on a linear function of the difference between condenser saturation temperature and condenser air inlet temperature agrees well with the experimental results for both systems. A simple control scheme was used to control subcooling by regulating the refrigerant flow with an electronic expansion valve and maximize the COP.

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Details

  • Original title: Effect of heat exchanger size on subcooling control in residential air conditioning systems.
  • Record ID : 30030644
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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