Comparitive analysis of an automotive air conditioning systems operating with CO2 and R134a

J. Steven Brown, Samuel F. Yana-Motta, Piotr A. Domanski

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199 Scopus citations

Abstract

This paper evaluates performance merits of CO2 and R134a automotive air conditioning systems using semi-theoretical cycle models. The R134a system had a current-production configuration, which consisted of a compressor, condenser, expansion device, and evaporator. The CO2 system was additionally equipped with a liquid-line/suction-line heat exchanger. Using these two systems, an effort was made to derive an equitable comparison of performance; the components in both systems were equivalent and differences in thermodynamic and transport properties were accounted for in the simulations. The analysis showed R134a having a better COP than CO2 with the COP disparity being dependent on compressor speed (system capacity) and ambient temperature. For a compressor speed of 1000 RPM, the COP of CO2 was lower by 21% at 32.2°C and by 34% at 48.9°C. At higher speeds and ambient temperatures, the COP disparity was even greater. The entropy generation calculations indicated that the large entropy generation in the gas cooler was the primary cause for the lower performance of CO2.

Original languageEnglish
Pages (from-to)19-32
Number of pages14
JournalInternational Journal of Refrigeration
Volume25
Issue number1
DOIs
StatePublished - Jan 2002
Externally publishedYes

Funding

The National Institute of Standards and Technology sponsored the study with partial support received from the Catholic University of Rio de Janeiro (Brazil) for S.F.Y.M's post-doctoral stay at NIST. The authors thank V. Payne and D. Yashar of NIST and D. Zietlow of Bradley University for their comments on the draft manuscript. Appendix The coefficients that appear in Kransnoshchekov et al.'s [37] correlation in Eq. (6) are given by: (A1) n= −48.3865106 P P cr −184.4985 log 10 P P cr +48.5062915 P P cr 0.74 (A2) b= −9.0586 P P cr −27.27997 log 10 P P cr +9.670075 P P cr (A3) j=−9.4638845 x 10 −6 P P cr 15 + 0.24072314 P P cr 6 + 0.089613245 P P cr 15 where P is the pressure and P cr is the critical pressure. Note: there is no physical significance to the functional form of these equations; they simply were developed to fit Krasnoshchekov et al.'s data [37] .

Keywords

  • Air conditioning
  • Automobile
  • CO
  • Performance
  • R134a

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