Averaged heat transfer resistance of the building envelope is the primary parameter that determines the energy saving characteristics of the building. At the phase of the building design it is usually taken into account that building must preserve heat effectively. It is mostly important in northern countries where cold seasons last for more than a half of year. Usually infrared methods are used to find mechanical defects of the building envelope. In this article an alternative way to describe the building envelope using infrared camera is presented. The method includes the determination of local heat engineering characteristics of the envelope using contact measurements and the determination of averaged heat transfer resistance of the buildings envelope using its infrared image.
A general solution of the inverse problem of nonstationary heat conductivity in multilayer objects based on Fourier expansion of time dependencies of the surface temperatures is considered. An example of a thermophysical properties determination in the case of a three-layer object is presented. An influence of the measuring equipment precision on the determined values of the characteristics is investigated. It is illustrated that the presented method provides a satisfactory precision in a wide range of amplitude values of measuring equipment noise.
Stephan's problem of a freezing front propagation inside a multilayer objects is discussed. For to solve this problem in practice numerical methods are used to integrate moisture and heat transfer equations while calculation of the current frost pane's coordinate inside external multilayer building envelopes whose surfaces' temperatures are measured over a while. When the Stephan's equation integration takes place, the phase transformation is taken into account by means of a sharp jump of the material's specific heat capacity at the point of the phase transformation. Examples of such calculation of the frost pane coordinate dependency of time inside multilayer constructions are presented. An algorithm of the current dew point coordinate determination inside multilayer objects is suggested.