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Cost optimization of thermoelectric sub-cooling in air-cooled CO2 air conditioners.

Number: pap. 2140

Author(s) : YAZAWA K., LIU Y., KURTULUS O., et al.

Summary

This paper presents a cost-effective enhancement of a trans-critical carbon dioxide (CO2) cycle in air-conditioning mode by utilizing a thermoelectric (TE) sub-cooler. It is well-documented that the cooling COP of the transcritical CO2 cycle decreases as the ambient air temperature significantly increases above the critical temperature of the refrigerant. A high gas cooler outlet temperature limits the enthalpy of evaporation so that the air-conditioning cooling performance is reduced. Sub-cooling is known as a mitigation method to this problem. However, adding a small-scale heat pump to a residential or light commercial air conditioner can be quite costly. Therefore, a TE solid-state sub-cooler is proposed. The TE cooling devices utilized in small temperature differences ranging from 5 to 15°C can be quite efficient since the intrinsic heat loss of the TE by heat conduction in reverse direction of pumping heat is minimal. Based on the prior work, the optimum design for cost-per-performance shows that the cost for sub-cooling is dominated by the heat exchangers and it is not by the TE material itself. The TE modules are compact and have a low thickness, which is in the range of a few mm. Hence the TE modules can be integrated into the form factor of a plate heat exchanger. In this study, the cooling COP of the CO2 air conditioner is enhanced by approximately 12% using an optimally designed TE sub-cooler at an ambient temperature of 30°C. This potential improvement is based on a figure-of-merit (ZT) of currently available TE materials (ZT~1). The seasonal COP is evaluated and shows a significant climate dependency of enhancement with TE subcooling assist. The analysis of the material mass based cost against performance shows a contradictive trend between the cost and the COP, hence the optimum cost effective design must exist depending on the practical conditions.

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Pages: 9

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Details

  • Original title: Cost optimization of thermoelectric sub-cooling in air-cooled CO2 air conditioners.
  • Record ID : 30018970
  • Languages: English
  • Source: 2016 Purdue Conferences. 16th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2016/07/11

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