A critical approach to the determination of optimal heat rejection pressure in transcritical systems

Luca Cecchinato (1) , Marco Corradi (1) , Silvia Minetto (1)

1 Dipartimento di Fisica Tecnica

In this paper the optimal energy efficiency and high cycle pressure problem in single stage refrigerating carbon dioxide vapour compressor units operating in transcritical conditions is addressed. Literature approximated solutions to the optimisation problem are analysed and critically discussed. A numerical model for CO heat exchangers and refrigerant systems is developed. Different gas coolers are simulated in order to investigate the effect of literature simplifying assumptions on the optimal pressure determination: the analysis showed a strong sensitivity of the gas cooler outlet temperature from the secondary fluid temperature, from its capacity rate and from the heat exchanger geometry. Nevertheless it resulted that approximated solutions obtained considering the carbon dioxide gas cooler outlet temperature as an independent variable behaved better than solutions correlating it to secondary fluid inlet temperature.

Mots clés: CO; Transcritical cycle; Optimisation; Refrigeration; Heat pump; Gas cooler

Luca Cecchinato, Marco Corradi, Silvia Minetto. A critical approach to the determination of optimal heat rejection pressure in transcritical systems. Applied Thermal Engineering, 2010, 30 (13), pp.1812. ⟨10.1016/j.applthermaleng.2010.04.015⟩. ⟨hal-00649893⟩