Feasibility of cool storage systems in refrigeration

In the present report the economic viability and technical feasibility of selected cool storage systems are considered. Cool storage has clear potential for several applications: in connection with air-conditioning systems, domestic refrigerating and freezing systems, commercially e.g., in the dairy and vegetable industries; and in deep freezing, as in the meat industry. Air-conditioning has limited significance in Finland. For this reason it was not investigated in this study. In domestic refrigeration and freezing two systems were investigated; a controlled cooling heating system and a simple built-in system in individual refrigerators and freezers. The central cooling/heating system in houses was found to be economically unattractive. It also has several technical drawbacks. The simple built-in system appeared to be promising. The amount of savings is rationally a function of the difference between day and night tariffs and the costs of installing an automatic switch and storage media. A problem with the application of cool storage in domestic refrigerators and freezers results from the absence of clear peak hours. In the vegetable and dairy industries cool storage also has considerable potential. Several systems were investigated in this respect and compared to the conventional system. The cool storage system using Cristopia balls, one of the most common commercial systems available in Europe, was not economical at a tariff difference of 10 p/kWh or more. The cost-effectiveness of the system, however, improved considerably when an outdoor heat exchanger was added to make use of natural low ambient temperatures. Further improvement in the economic viability of the system was achieved when a sub-cooling system using outdoor temperatures was added. Still, the investment costs of the Cristopia system seem too high to justify the cool storage. A cheaper cool storage system could make the cool storage application more attractive. Cool storage for freezing in meat plants was also investigated. Again, in view of the relatively high costs of the Cristopia balls, the connection of such a cool storage system to existing plants was economically unattractive. Cheaper cool storage systems may be more attractive. On the other hand, even the cool storage system using Cristopia balls was found to be economically attractive when its size was optimised with the plant power in a new plant. When the net annual savings were about FIM 170 000 and the pay back period was about 6 years. More savings are expected from the cheaper cool storage system than from the Cristopia system.