Experimental optimization of defrosting duration for enhanced energy efficiency in large-scale ammonia-based tube ice-making systems

Abstract

This study experimentally investigates the impact of defrosting duration on the operational performance and energy efficiency of an industrial-scale 80-ton-per-day ammonia (NH3)-based tube ice-making system with a tube diameter of 38 mm. Experiments were performed under controlled ambient conditions (28 °C dry bulb temperature and 80% relative humidity) with defrosting times of 5, 6, and 7 min. Key performance indicators, including suction and discharge pressures, temperatures, power consumption, cooling capacity, freezing time, ice weight per cycle, and the coefficient of performance (COP), were systematically monitored. Each experiment was repeated three times (n = 3), and the results are reported as mean ± standard deviation. Results indicate that extending defrosting time beyond 5 min increases discharge pressure by up to 9% and discharge temperature by up to 12 °C, leading to a 3.14–9.52% rise in compressor energy consumption. At the same time, cooling capacity decreased by 2.8% (6 min) and 7.1% (7 min), lengthening freezing cycles and reducing daily ice production by 4–10% compared with the 5-minute baseline. Although slightly more ice mass per cycle was achieved with longer defrosts, this advantage was offset by higher energy demand and lower cooling efficiency. The findings underscore the importance of optimizing defrosting duration to achieve an effective balance between energy consumption and production efficiency in industrial ice-making systems. Furthermore, thermo-hydraulic evaluation using SEC confirms that a 5-minute defrost duration optimally balances energy efficiency and production capacity, providing a validated experimental benchmark for defrost optimization in large-scale ammonia-based tube ice systems.