Thermodynamic analysis of the refrigeration cycle of a domestic freezer with an electronic expansion valve

• EEV behaviour in domestic refrigeration cycles under varying conditions. • Discussion of operating domestic EEV systems near thermodynamic optimum. • Thermodynamic optimum requires HX outlet near refrigerant phase boundary. • EEV enables efficient operation at 32 °C and 16 °C ambient temperature. Electronic expansion valves (EEVs) can improve the energy efficiency of domestic refrigerators by allowing the refrigeration cycle to operate closer to its thermodynamic optimum across a wide range of operating points — unlike traditional capillary tubes, which are optimized to a single design point. However, the component interactions under such varying conditions are highly complex, and understanding them is crucial for efficient operation. A 0D–1D in-house simulation model, validated against experimental data, was used to investigate the refrigeration cycle behaviour of a domestic freezer with an EEV. In this model, outlet conditions of evaporator and high-pressure side heat exchangers are not fixed but emerge from the cycle calculation. A total of 39 operating points were simulated with varying operating parameters, including compressor speed, fan speeds, EEV opening ratio and refrigerant charge. Energy consumption was evaluated, followed by an in-depth analysis of internal cycle behaviour. The results show that efficient operation is achieved when the heat exchangers operate near the refrigerant phase boundaries: saturated vapour at the evaporator outlet (vapour quality ≈ 1) and saturated liquid at the high-pressure side outlet after the heat loop (vapour quality ≈ 0). Deviation too far into the two-phase region significantly increases energy consumption, while superheating or subcooling has a smaller effect. For both 950 and 1250 rpm compressor speeds, as well as ambient temperatures of 16 and 32 °C, the EEV enabled efficient operation of the refrigeration cycle. These results may be useful for implementing EEVs in domestic refrigerators and developing EEV control strategies.