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Theoretical investigation on the combined and cascade CO2/R134a heat pump systems for space heating


Song, Y and Li, D and Cao, F and Wang, X, Theoretical investigation on the combined and cascade CO2/R134a heat pump systems for space heating, Applied Thermal Engineering, 124 pp. 1457-1470. ISSN 1359-4311 (2017) [Refereed Article]

Copyright Statement

Copyright 2017 Elsevier Ltd.

DOI: doi:10.1016/j.applthermaleng.2017.06.014


In this study, comparison between combined and cascade CO2/R134a heat pump systems were investigated theoretically. The characteristics of the R134a and CO2 cycles in both combined and cascade systems were studied under different working conditions. The evaporation temperature in the R134a cycle and the discharge pressure in the CO2 cycle were first evaluated in the combined and cascade systems. Results showed that the change of the R134a evaporation temperature in the cascade system was much larger than that in the combined system as the hot water supply temperature increased from 55 to 75 C. The CO2 discharge pressures in the cascade system were much lower than those in the combined system under all working conditions. The heating capacity in the two cycles was then examined in the two systems. The results showed that the CO2 cycle played the major role in the combined system while the R134a cycle played the major role in the cascade system. The system COP comparison showed that the cascade system performed better under relatively low ambient and hot water supply temperatures whilst the combined system performed better under high hot water supply temperatures. The compressor displacement ratio comparison results showed that the combined system would be much more environmentally friendly in comparison to the cascade system.

Item Details

Item Type:Refereed Article
Keywords:transcritical CO2 cycle, cascade heat pump, combined heat pump, space heating, performance
Research Division:Engineering
Research Group:Mechanical engineering
Research Field:Energy generation, conversion and storage (excl. chemical and electrical)
Objective Division:Energy
Objective Group:Energy efficiency
Objective Field:Residential energy efficiency
UTAS Author:Wang, X (Professor Xiaolin Wang)
ID Code:118725
Year Published:2017
Web of Science® Times Cited:25
Deposited By:Engineering
Deposited On:2017-07-18
Last Modified:2018-06-26

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