Study on effect of operating time for thermal storage based on building envelope

Most buildings are constructed with concrete. The thermal capacity of such elements in buildings provides the possibility to store thermal energy. In this study, the character of cold storage based on building envelope was explored. The TRNSYS model was set up based on an actual office building with a floor radiant cooling system, which normally opens during 8:00-18:00 on workdays. The local peak period for electricity is 16:00-22:00, the valley tariff period is 2:00-8:00, and the parity period is 8:00-16:00 during cooling. Based on the peak-valley electricity price, four operating strategies of cold storage were proposed, namely, condition 1 (2:00-8:00), condition 2 (2:00-10:00), condition 3 (2:00-12:00), and condition 4(2:00-14:00). The simulation showed that under the cold thermal storage conditions, the indoor air temperature was lower in the morning and kept increasing during working time, which led to temperature drift in the office room. For condition 1 and 2, the indoor thermal comfort cannot be assured as indoor temperature can be higher than the comfort level in later afternoon. For condition 3 and 4, the thermal comfort was better, and the PMV index can be kept in the range of -1 to 1 all the time. Results of thermal balance showed that the cold can be stored both in the cooling floor and internal walls by reduced the structure temperature, and the cooling loss during night was less than 10%. The running cost of both condition 3 and 4 were lower than the normal condition. Condition 3 (with same running time of the normal condition) had better economic effect, in which running cost was reduced by 16.2%. The results provided information for the cost saving operation of radiant cooling systems based on building envelope cold storage.