Ideal thermophysical properties of building wall: Method based on impedance and interpretation mechanism

摘要

Thermal resistance is commonly defined as the ratio of the temperature difference to the heat flow, and it is only valid for one-dimensional, steady heat conduction without an internal source. This work extends the application scope of the thermal resistance to the multi-dimensional, unsteady conditions based on the entransy dissipation rate, which is called impedance. It provides an approach to optimize the heat transfer process of complex problems. For example, it can be used to analyse the unsteady heat transfer of building envelope: when the indoor and outdoor temperature difference is given, the extremum of building envelope thermal resistance is corresponding to the extremum of heat input to the interior from envelope, which is determined by the ideal volumetric specific heat distribution versus temperature of building envelope. Based on this, the relationship between thermal resistance and volumetric specific heat of building envelope is developed, and according to the extremum of thermal resistance, the ideal volumetric specific heat can be obtained. In this paper, applications are presented for active and passive conditions. The results show that, for active or passive condition, the ideal volumetric specific heat of the external wall should be a function in summer or winter.