Comparative Analysis of the Energy Efficiency of Refrigeration Systems with R744 (CO₂) and R717 (Ammonia) Refrigerants for Ice Rinks

Abstract

Ice rinks are highly energy-intensive facilities, and current trends in refrigeration engineering increasingly focus on the use of natural refrigerants to improve energy efficiency while complying with environmental and legal regulations. Among these solutions, ammonia (R717) and carbon dioxide (R744) are widely considered state-of-the-art options for large-scale ice rink applications. The aim of this study is to compare the energy efficiency of two refrigeration systems based on natural refrigerants: R717 and R744, designed to supply an ice rink compliant with International Ice Hockey Federation (IIHF) standards. The study sought to determine whether significant differences in energy performance and operating costs exist between the two systems under realistic operating conditions. The analysis included a detailed thermal load calculation of the ice rink, accounting for all major heat gains such as heat transfer from the hall to the ice slab, occupants, lighting, ventilation, and ice-resurfacing machinery. Heat gains were divided into loads affecting the air and those directly impacting the ice surface. Thermal balance calculations were performed for two operating scenarios: steady-state rink operation and the ice-freezing process. Variable operating conditions, including changes in user occupancy and different usage scenarios (weekdays, weekends, and sporting events), were also considered. Two refrigeration configurations were analyzed: a transcritical CO₂ system with Flash Gas Bypass and an ammonia system with a flooded evaporator. Energy performance was evaluated using EER and SEER indicators, along with annual electricity consumption. The results showed that the ammonia-based system achieved higher energy efficiency and lower annual electricity consumption compared to the CO₂-based system, resulting in reduced operating costs. Conversely, the CO₂ system offered superior operational safety due to the non-toxic and non-flammable nature of the refrigerant, which may be particularly advantageous in densely populated areas. The findings indicate that the selection of a refrigeration system for ice rinks should be based on investor priorities and site-specific conditions. Ammonia systems are preferable where high efficiency and low operating costs are critical, while CO₂ systems are more suitable where maximum safety is required. For the analyzed ice rink, located away from residential areas, the ammonia system proved to be the more economically favorable solution. The results may support future refrigeration system designs and suggest that further efficiency improvements could be achieved through multi-stage or cascade system configurations.