An air conditioning system that actively utilizes the heat capacity of the building frame (building thermal mass storage system) has a history of almost 100 years. Until now, in Japan, models and research results have been primarily obtained by blowing cold and hot wind against a concrete structure using fans. In recent years, technologies capable of efficiently producing medium-temperature cold water have progressed, and the technology of humidity control has been enhanced by separating the sensible and latent heat components. Therefore, building thermal storage systems in which piping is embedded in the building structure and cold water is directly introduced into the embedded pipes are increasingly being adopted. Compared to the commonly used convection air conditioning system, the building thermal mass storage system is expected to improve the radiant thermal environment in the building and efficiency of the system by reducing the air transfer fan power. However, to the best of our knowledge, there are few studies that report comparisons on these points. Therefore, in this study, we first developed a model using the measured values of the building thermal mass storage system installed in an office building in Tokyo. The maximum error values for temperature and heat flow were 0.2 °C and 1.8 W/(m2·K), respectively, and the average error values were respectively 0.6 °C and 4.3 W/(m2·K). Next, by comparing the calculated result of this model with the results from the convection air conditioning system model, the differences in the thermal environment of the room and energy consumption were verified. In the case where the dry-bulb temperature was maintained at a constant value, the Predicted Mean Vote (PMV) of the convection air- conditioning system was higher by an average of about 0.3 compared with that of the building thermal mass storage system. In addition, when the PMV was maintained constant, it was confirmed that the difference between the mean radiant temperature and dry-bulb temperature was large in the convection system. Based on the heat load obtained using simulations, energy consumption was compared between the convection system and building thermal mass storage system. The system coefficient of performance (COP) ratio was calculated by changing the heat source COP and heat transfer efficiency. If the water transfer factor (WTF) at the time of thermal storage is not extremely low, the energy consumption of the building thermal mass storage system is lower than that of the convection system.
