Study on utilization of cold energy from natural ice—Ice-making efficiency of small ice containers stacked in a cold room

Recently, the efficient use of cold energy, a type of natural energy derived from snow and ice, has been studied as an energy-saving measure to cut emissions of carbon dioxide. For example, the Ice Shelter, which is constructed with natural ice, was developed to create an environment with low ambient temperature and high humidity using latent heat absorbed or released during the phase change of water throughout the year. Because the low temperatures and high humidity maintained by the Ice Shelter is suitable for long-term storage of farm products, it is expected to be put to practical use as a new energy-saving storage technique for farm products. However, there are some technical problems that must be solved first. One of these is the establishment of an ice-making technique that uses naturally cold air of winter efficiently and freezes the water consistently in the ice containers. In this study, we used stacked ice containers to model the actual conditions of an Ice Shelter. We found that the freezing process was completed sequentially from the lowest to the highest containers and that the ice-making efficiency calculated from outside temperature was lower at the upper steps. However, when the calculation was made from ambient temperature between the containers, we found that there was little difference in the ice-making efficiency of each container. For this reason, we assumed that the ice-making efficiency of all the containers was substantially the same and modeled the process to account for the effect of latent heat produced by the freezing process in the lower containers on the process in the upper containers. Like the observed values, the estimated values of air temperature between the containers decreased as the freezing process terminated sequentially from the lowest to the highest containers because the influence of latent heat became small as ice making proceeded from the lowest to the highest containers. Thus, the model successfully approximated the influence of latent heat on the freezing process in stacked ice containers.