We have developed a heat pipe type artificial permafrost storage system by utilizing cold energy at winter time. At first, basic tests of forming frozen soil using a 8 m length corrugated heat pipe were carried out. Thereby, it was found that the temperatures of the heat pipe became uniform and the surrounding soil could be frozen uniformly.
In December 1987, an experimental plant for proof tests was constructed in Hokkaido. Around the storage facility, heat pipes were installed into the ground at the intervals of 0.5 meter and the condensing sections were installed in atmosphere. In winter of the year, frozen soil was smoothly formed. At the end of January, 2 m thick frozen soil layer was completed. Even in July, the soil temperature was kept about -1°C and the storeroom temperature was also kept about 3 to 4°C. The similar result was also obtained in the winter of 1988 to 1989 (freezing index: Approx. 550°C-day). Moreover, it was found that the cold storage which uses heat pipes is sufficiently applicable since the temperature and humidity inside the storage can maintain the conditions necessary for storage of agricultural products.