The Effects of a Selective Heat Exchange Circuit on Ice Accumulation in Cold Climate Heat Pumps

When heat pumps operate for extended periods in cold climates, ice tends to accumulate at the bottom of the outdoor heat exchanger, leading to degradation in system performance and reliability. To address this issue, various studies have been conducted; however, the complexity of the system architecture and control strategies has remained a significant challenge. In this study, we propose a passive refrigerant flow control method based on a selective heat exchange circuit (SHEC) that integrates a check valve, capillary tube, and a modified tube circuit. The proposed method automatically switches the refrigerant flow path according to the operating mode, thereby suppressing frost accumulation without the need for additional controllers or sensors. Owing to its simple structure, the method demonstrates high potential for practical and commercial application. Its effectiveness was verified through laboratory and field tests conducted in Fairbanks, Alaska. In the lab-scale experiments, ice accumulation was restricted at the bottom of the outdoor heat exchanger during the operation for 400 min at -15 °C, with a relative humidity of 85%. The heating efficiency increased by up to 8.3% under partial-load conditions across various outdoor temperatures, primarily due to the improved refrigerant mass flow distribution in the outdoor heat exchanger achieved through the installation of the proposed circuit. In field tests conducted from January to April 2024, the system performance was maintained as designed and evaluated under similar outdoor weather conditions on different days. A passive selective heat exchange circuit (SHEC) was proposed to automatically control refrigerant flow in heat pumps, effectively suppressing frost accumulation on outdoor heat exchangers and improving heating efficiency by up to 8.3% under cold-climate conditions without additional sensors or controllers.