CALCULATION OF OPERATING PARAMETERS OF A TWO-STAGE CO₂ HEAT PUMP FOR BUILDING HEATING SYSTEMS

• Date: 2026
• Main Authors: Basok , B., Zurian , O., Dubovskyi , S., Krukovskyi , H., Skliarenko, D., Pastushenko , E., Imran , M.
• Format: Article
• Language: Ukrainian
• Published: Institute of Renewable Energy National Academy of Sciences of Ukraine 2026
• Subjects: Renewable energy; heat pump; cascade heat pump system; two-stage heat pump; building heating system; refrigerant; computer simulation; Flownex SE; coefficient of performance.
• Online Access: https://ve.org.ua/index.php/journal/article/view/642
• Journal Title: Vidnovluvana energetika

The paper investigates the operating parameters of a two-stage, dual-circuit air-to-water heat pump system intended for heating an administrative building. The first circuit of the system uses refrigerant R744 (CO₂), while the second circuit operates with refrigerant R513a. The aim of the study is to determine the key operating parameters of a heat pump unit with a thermal capacity of about 120 kW and to assess the feasibility of its application in building heating systems with conventional radiator heating devices. To analyze the system operation, a computational model of the heat pump was developed in the Flownex SE simulation environment, which allows modeling thermohydraulic processes in a dual-circuit system considering the characteristics of compressors, heat exchangers, and control elements. Based on numerical simulations, the dependencies of the heat pump thermal capacity, refrigerant mass flow rates, compressor rotational speed, and coefficient of performance on the outdoor air temperature in the range from –25 °C to +10 °C were determined. Thermohydraulic processes during the operation of the two-stage dual-circuit air-to-water heat pump were calculated, and validation of the developed model was performed by additional simulation of the Mitsubishi ESA30E-25 heat pump. The obtained results demonstrate the features of operating modes of the first and second circuits of the heat pump system under different temperature conditions and allow evaluation of the efficiency of a cascade configuration using refrigerants R744 and R513a for building heat supply systems. The practical novelty of the work lies in the application of the developed model for preliminary determination of component parameters and control strategies of the considered heat pump system used for building heating.