Thermal storage in building mass (TSBM), which stores thermal energy in building components such as floor slabs or structural beams by AHUs, discharges the stored thermal energy mainly in the morning and seems to be suitable to reduce large thermal load which emerges in the stand-up period of HVAC operation for heating. A field study in winter conducted in an office building located in Sapporo, Japan, shows the temperature descent of floor slabs in weekend and the cause was supposed to be the cooling by outdoor climate. It leads to the increase of stored thermal load on Monday morning, which was verified also by the increase of electrical consumption of HVAC heat source. The thermal energy supplied by AHUs in storage period was larger than that in normal operation in the field study and the AHU capacity for TSBM will be minimized when the minimum hourly thermal load of the storage period is equal to that of the normal operation period. A simulation study was conducted to show the method to minimize the AHU capacity. The study also shows that the minimum capacity brings the minimum increase of the thermal energy supplied by HVAC system.
