Evaluation of heat recovery performance in a CO2 ice rink.

Ice rinks have a high coinciding cooling and heating demand which turns them into ideal heat recovery applications. Using carbon dioxide (CO2) as a refrigerant in a trans-critical refrigeration system allows the ice rink to be self-sufficient in terms of heat. High temperatures can be supplied which in combination with a suitable heating system design can result in very high heat recovery performance. This study is based on the system solution used in the Gimo ice rink, first of its kind in Europe, using a 100% CO2 trans-critical system, with direct expansion. This system is designed with a temperature cascade on the heat recovery side to fit the CO2 properties. This implies a low return temperature from the heating system to increase the sub-cooling and thus the system efficiency. To further improve efficiency and the return from the heat recovery system a geothermal storage equips the installation as well. A numerical model has been created using real data from the field which allows to compare actual operating parameters with the desired optimal values. The aim is to find the optimum control of the head pressure and the sub-cooling to reach the maximum overall efficiency at all conditions. The results suggests that the heat recovery coefficient of performance is in the range 3.5-4, which is in line with or exceeds most conventional heat pumps considering the relatively high supply temperature of 60°C. An advantage is that this system solution does not need supplementary heat or heating equipment – one system covers the complete refrigeration and heating function.