A Dynamic Prediction Model For The Effective Thermal Capacity Of Buildings And Its Application Analysis In Typical Thermal Processes

Indoor thermal environment and air conditioning energy consumption can be significantly influenced by thermal mass.Thermal mass can be used to improve the indoor thermal environment and reduce the energy consumption of air conditioning.The necessary condition for reducing the energy consumption is to predict how much of the building thermal mass is involved in heat transfer process（i.e.,effective thermal capacity（ETC））and to understand the relationship between the ETC and the indoor thermal environment.The lack of methods to predict the ETC of building quickly and accurately has resulted in few applications of ETC,although the ETC of building plays an important role in selecting envelope types,determining heating patterns,and analyzing natural ventilation characteristics.A quick and accurate prediction of the ETC would facilitate the implementation and application of building thermal standards for ETC.In this paper,the function of thermal mass is systematically analyzed,a theoretical model for predicting the building ETC is developed by using a combination of mathematical theory derivation,Energy Plus software and experimental testing.A dynamic prediction model for the building ETC is extended and applied to study of several typical thermal processes,i.e.,natural ventilation and intermittent heating.This model can provide thermal designer with a theoretical basis for the design of natural ventilation system,intermittent heating strategy and the optimization design of building envelope structure.The prediction of the building ETC is the key parameter to use of the thermal mass.So,the temperature elasticity coefficient（TEC）is adopted to describe the relationship between the inner surface temperature of the external wall and the indoor air temperature.The ETC is then introduced to quantify the thermal mass of the building.A dynamic ETC prediction model was developed by integrating the ETC and TEC.Then the effects of various factors on the ETC and TEC were investigated.The ETC and TEC in the dynamic ETC prediction model are found to be independent of outdoor air temperature,solar radiation,and indoor heat source intensity.The ETC is mainly related to the insulation location,the wall thermal resistance,air change rate and window-wall ratio.The TEC is mainly determined by insulation location and wall thermal resistance.A simple and effective way to reduce the energy consumption of air conditioning is to increase the thermal comfort hours of the natural ventilation.The thermal comfort hours are related to the building ETC.However,the existing studies ignore the ETC of the exterior walls,which assumes that there are no windows on the exterior walls and the exterior walls are adiabatic or the room are involved only indoor ETC.These assumptions lead to the overestimation of the decrement factor of indoor air temperature and the underestimation of the time lag.In this paper,the dynamic ETC prediction model is applied to predict the heat transfer process of naturally ventilated,and the relationship between ETC and indoor air temperature is further obtained when the outdoor air temperature fluctuates periodically.The error caused by the existing natural ventilation model ignoring the ETC of external walls and heat transfer through windows are compensated.When there are no windows in the exterior walls and the walls are insulated or only the interior ETC is considered,the dynamic building ETC prediction model in this paper can obtain similar results to existing studies.The influencing factors of ETC and TEC are analyzed and a database model of ETC and TEC is established by using mathematical statistical methods.An effective approach to reduce the heat loss through the external wall is to optimize the thermal performance of external wall.One of the simplest and most effective ways to achieve energy savings in buildings is to increase the time lag and damping factor of walls by optimizing the location and distribution of insulation layer.Time lag and damping factor are the key parameters for assessing the thermal performance of exterior walls and an important input parameter for modeling in this paper,is greatly influenced by the wall insulation and affected the energy efficiency of the building.To optimize the location and distribution of insulation layers,a combinatorial algorithm is adopted to determine all wall structures,and transient heat conduction equation is solved by using the thermal quadrupole method.The multi-objective algorithm is then adopted to determine the best wall configuration with consideration of maximum time lag and damping factor.Time lag and damping factor of the wall structure with evenly distributed insulation layers are larger than that with unevenly distributed layers.When the insulation layer is split into one,two and three layers,time lag and damping factor of the best wall structures decrease with decreasing the number of insulation layer.The higher the number of insulation splits,the larger the time lag and damping factor.The part-time-part-space heating operation model（i.e.,intermittent heating）is commonly used in the Hot Summer and Cold Winter（HSCW）zone of China.The ETC of the building（thermal storage and release process）has a great influence on energy consumption.Therefore,by comparing the heating loads of intermittent heating and continuous heating,the possibility of a critical heating time ratio was found to exist.However,due to the complex calculation of critical heating time,the critical heating time ratio is not used to standardize the heating strategies of actual buildings.To reduce building energy consumption in HSCW areas,this paper applies the dynamic ETC prediction model to study the critical heating problem under intermittent heating mode and provides a critical heating time ratio model to predict the critical heating time ratios of different buildings.The results show that the critical heating time ratio is mainly related to the ETC,the TEC of the inner wall surface of the envelope structure.The critical heating time ratio of external wall insulation method is larger than that of internal insulation.The critical heating time ratio decreases with the increase of thermal resistance and air changes rate.The theoretical expression of ETC is not clear,which will seriously prevent the provisions of building energy efficiency standards on heat capacity of exterior wall in projects.Therefore,a theoretical analysis of the bidirectional heat transfer in the wall is conducted,and the general solution of the ETC of the single-layer wall is obtained by introducing the auxiliary equation.The potential influencing factors of the ETC are obtained through a rigorous theoretical analysis,and it is found that the ETC is strongly related to the thermal storage coefficient.The thermal storage coefficient is influenced by the initial phase difference,the decrement factor,and the ratio of indoor and outdoor convective heat transfer coefficients.When the initial phase difference is ?/2or ?,the initial phase difference was found to interfere with the heat transfer between the exterior thermal mass and the indoor air.