TY - JOUR
T1 - Subcooling effect on the optimal performance for a transcritical CO2 heat pump with cold thermal energy storage
AU - Wang, Ji
AU - Evans, Michael
AU - Belusko, Martin
AU - Zhao, Chunrong
AU - Liu, Ming
AU - Bruno, Frank
N1 - Funding Information:
The authors would like to acknowledge the Australian Government for the Research Training Program (RTP) scholarship. The author: Ji Wang, would also like to thank Dr Ming Liu from the University of South Australia for giving the explanations on selecting intermittent heat transfer fluid and phase change material (PCM) for cold thermal energy storage (CTES).
Funding Information:
The author would like to acknowledge the Australian Government for the Research Training Program (RTP) scholarship. The author declares that no other funds, grants, or other support were received during the preparation of this manuscript.
PY - 2023/7
Y1 - 2023/7
N2 - This paper studies the combined heating and cooling thermal performance of a CO2 heat pump system considering the subcooling effect. For such a system without cold thermal energy storage (CTES), the gas cooler outlet temperature normally needs to be controlled to match the cooling load required. However, the integration of CTES would enable the system to be operated under its optimal conditions depending on the ambient temperatures, i.e. a considerable amount of cooling capacity can be generated and stored for later use. A configuration of a CO2 heat pump integrated with CTES is described in this paper. A thermodynamic cycle and a simulation model considering the subcooling effect have been developed. The mathematical model for the pinch point analysis has been newly validated against published experimental data with acceptable agreements. In the case study, the impacts of the subcooling temperature on the optimal combined performance under four ambient temperatures (5 °C, 15 °C, 25 °C, and 32 °C) have been studied. The highest optimal combined COP of 5.38 can be achieved when the ambient temperature is 5 °C. The detailed profiles of CO2 temperatures, heating and cooling loads, and the COPs when the CTES is in operation have been revealed for the first time. It is found when the ambient temperature is higher than the water inlet temperature (plus the pinch point temperature), the optimal cooling COPs can even have a surge without the subcooling effect, due to a lower sCO2 temperature leaving the heat exchanger compared to the ambient temperature. Additionally, performance analysis for the CO2 heat pump system with or without CTES is compared, and it is concluded that all optimal heating, cooling, and combined COPs integrated with CTES surpass those without CTES.
AB - This paper studies the combined heating and cooling thermal performance of a CO2 heat pump system considering the subcooling effect. For such a system without cold thermal energy storage (CTES), the gas cooler outlet temperature normally needs to be controlled to match the cooling load required. However, the integration of CTES would enable the system to be operated under its optimal conditions depending on the ambient temperatures, i.e. a considerable amount of cooling capacity can be generated and stored for later use. A configuration of a CO2 heat pump integrated with CTES is described in this paper. A thermodynamic cycle and a simulation model considering the subcooling effect have been developed. The mathematical model for the pinch point analysis has been newly validated against published experimental data with acceptable agreements. In the case study, the impacts of the subcooling temperature on the optimal combined performance under four ambient temperatures (5 °C, 15 °C, 25 °C, and 32 °C) have been studied. The highest optimal combined COP of 5.38 can be achieved when the ambient temperature is 5 °C. The detailed profiles of CO2 temperatures, heating and cooling loads, and the COPs when the CTES is in operation have been revealed for the first time. It is found when the ambient temperature is higher than the water inlet temperature (plus the pinch point temperature), the optimal cooling COPs can even have a surge without the subcooling effect, due to a lower sCO2 temperature leaving the heat exchanger compared to the ambient temperature. Additionally, performance analysis for the CO2 heat pump system with or without CTES is compared, and it is concluded that all optimal heating, cooling, and combined COPs integrated with CTES surpass those without CTES.
KW - Cold thermal energy storage
KW - Simultaneous heating and cooling
KW - Subcooling effect
KW - Transcritical CO heat pump
U2 - 10.1007/s00231-022-03333-9
DO - 10.1007/s00231-022-03333-9
M3 - Journal article
AN - SCOPUS:85144211225
SN - 0947-7411
VL - 59
SP - 1257
EP - 1275
JO - Heat and Mass Transfer
JF - Heat and Mass Transfer
IS - 7
ER -