A New Method of Regulating the Cooling Capacity of a Cooling System with CO 2

Artur Bieniek, Jan Kuchmacz, Karol Sztekler, Lukasz Mika and Ewelina Radomska
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Artur Bieniek: Department of Thermal and Fluid Flow Machines, Faculty of Energy and Fuels, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059 Cracow, Poland
Jan Kuchmacz: Division of Refrigeration and Air Conditioning, Institute of Thermal and Process Engineering, Faculty of Mechanical Engineering, Cracow University of Technology, Jana Pawla II 37 Av., 31-864 Cracow, Poland
Karol Sztekler: Department of Thermal and Fluid Flow Machines, Faculty of Energy and Fuels, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059 Cracow, Poland
Lukasz Mika: Department of Thermal and Fluid Flow Machines, Faculty of Energy and Fuels, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059 Cracow, Poland
Ewelina Radomska: Department of Thermal and Fluid Flow Machines, Faculty of Energy and Fuels, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059 Cracow, Poland

Energies, 2021, vol. 14, issue 7, 1-18

Abstract: New guidelines set by international organizations for refrigeration companies cause that natural working fluids such as carbon dioxide are increasingly used in new refrigeration systems. Carbon dioxide (R-744) is used in freezing, cooling, or air conditioning installations, in which the cooling load fluctuates hourly. To adapt the cooling capacity of the evaporator to the current cooling load of the cooled space, a number of control elements are used. The paper proposes a new method of regulating the cooling capacity for a one-stage refrigeration cycle with the R-744 refrigerant and an internal heat exchanger (IHX). The proposed method involves using an additional evaporator and combines the possibility of regulating the cooling capacity with the possibility of energy efficiency ratio (EER) improvement. The energy analysis of the proposed method of regulating the cooling capacity was performed and the results were compared with the control method. The control method was using the compressor hot gas bypass valve which allows the flow of hot vapor refrigerant to the suction side. The energy analysis was carried out for both subcritical and supercritical cycles using the energy equations. For each of the considered methods, the characteristics of the change in the EER as a function of the reduction of the cooling capacity in both supercritical and subcritical cycles were determined. It was found that when the cooling capacity decreased by 50%, the hot gas bypass regulating method was around 30% less efficient compared to the proposed additional evaporator regulating method.

Keywords: carbon dioxide; cooling capacity; energy efficiency ratio; hot gas bypass valve; R-744; transcritical cycle (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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