Experimental analysis of a transcritical heat pump system with CO2 refrigerant

Abstract

Today, it is seen that increasing environmental pollution is getting ahead of the increasing energy need. Therefore, more environmentally friendly and more economical refrigerants are needed. In this context, carbon dioxide appears as a natural refrigerant in cooling systems and heat pump (HP) systems, and it has been widely used in recent years. In this study, a single-stage heat pump system with a CO2 refrigerant, with a transcritical cycle, has been experimentally studied. The system is designed as a water-to-water heat pump. The performance of the system has been determined experimentally. In the system, capillary pipes with a diameter of 2.00 mm and two different lengths are used. It is aimed to create different evaporation pressures with two capillary tubes. The first capillary tube is 2.40 m long and the second is 1.20 m long. Gas cooler pressures, gas cooler and evaporator cooling water mass flow rates were kept the same for both cases. A certain gas charge was made and measurements were made for both cases. Thermodynamic analysis and comparison of the system were made. In the short capillary tube system, it was observed that the COPHP value was 7.2% higher, the CO2 mass flow rate increased by 9.1% to achieve the same gas refrigerant pressure value, and the power consumption in the compressor decreased by 1.8%. In addition, the gas cooler outlet temperature, the evaporator outlet temperature and the change in ambient temperatures, as well as the exergetic destruction and exergetic efficiencies in the system and system components are presented in figures with EES.