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On the existence of optimal intermediate temperature in two-stage vapor compression systems

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  • Ma, Chi-Yuan
  • Kezier, Deliya
  • Zhang, Chun-Lu

Abstract

Vapor compression systems are widely used in air conditioning, refrigeration, and heating, with two-stage systems often used in applications where a large temperature lift is required to improve energy efficiency. Optimization of the intermediate temperature (Tint) is critical to maximize the system energy performance. This paper investigates the existence of optimal Tint in two-stage systems. A general thermodynamic model is developed using the cycle separation method, followed by theoretical derivation and numerical validation. The results reveal four different functional relations between the coefficient of performance (COP) and Tint, which are influenced by isentropic efficiencies, operating conditions, and thermodynamic properties of refrigerants. An optimal Tint exists only when the isentropic efficiencies of both stages are comparable and not excessively low. Conversely, significant differences in isentropic efficiencies or both low efficiencies result in the absence of optimal Tint. This paper introduces a general thermodynamic model for two-stage systems and identifies four unique Tint-COP relations, providing broader insights compared to previous studies that predominantly focused on specific configurations. Accordingly, some fundamental recommendations for the design and operation of two-stage systems are made.

Suggested Citation

  • Ma, Chi-Yuan & Kezier, Deliya & Zhang, Chun-Lu, 2025. "On the existence of optimal intermediate temperature in two-stage vapor compression systems," Energy, Elsevier, vol. 315(C).
    • Handle: RePEc:eee:energy:v:315:y:2025:i:c:s0360544225001239
    DOI: 10.1016/j.energy.2025.134481
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