Study On Characteristics Of Coupled Heat And Moisture In Porous Building Materials

The thermal and moisture performance of the porous building materials are closely related to the building energy consumption and indoor thermal and moisture environment. In order to build low energy consumption building and achieve low carbon economy, it is really important to design adaptive envelope structure considering the thermal and moisture performance of the porous building materials. But, it is truly difficult to choose reasonable and energy saving envelope structure because the material property parameters, especially that of the new polymeric chemistry building materials is very short. In this paper, the method to determinate material property parameters is comprehensively studied financed by the national natural science funds project THE STUDY OF THERMAL PHYSICAL PROPERTIES AND PYROLOGY DESIGN CALCULATION OF NEW ENERGY-SAVING BUILDING STRUCTURE (50678163). The expression of vapor and liquid water diffusion coefficient were deduced and tested, and the thermal performance of epidermis climate layer envelope constructure is computed. The main work is as follows:1. The expression of water vapor diffusion coefficient and liquid water diffusion coefficient is derived based on the serial-parallel model and the analysis of electronic scanning images. The liquid water diffusion coefficient is expressed by water uptake coefficient, so the water vapor diffusion coefficient and liquid water diffusion coefficient are separated. The parameter identification is applied to calculate the both coefficients.2. The balanced moisture of porous material is researched. Based on the GAUSS model, the relationship between the material moisture content and air relative humidity, namely the moisture storage function, in the whole material moisture content is studied. The moisture storage function includes two parts, the hygroscopic and the overhygroscopic moisture range, which avoids the shortcomings of routine isothermal cure that contains only hygroscopic stage information. It provides a solid tool for calculating liquid water and water vapor transmission simultaneously and makes it possible to analyze the influence of climate such as rain and snow on the durability and energy consumption of buildings.3. The method of measuring material physical parameter is studied. The test method according to ISO is selected and developed. (1) The test methods and test conditions of water uptake coefficient and liquid water diffusion coefficient were studied and were applied to study the water vapor diffusion rate and the liquid water diffusion rate of cement mortar. (2) The subsection testing method of moisture contents and the approach of obtaining relative humidity artificially were studied. (3) A new method of testing conduction coefficient dynamically and its test procedure were obtained by developing the method of testing conduction coefficient using heat flow plan after considering the influence of environmental humidity on test. (4) The method to measure the material porosity is discussed. By analyzing the advantages and disadvantages of several methods including the directly measure volume method, statistics method, mercury injection method, density method and suck permeability method, the suction permeability method is chosen to measure the porosity.4. The basic property parameters of new thermal insulation mortar were tested. The moisture storage function, water vapor diffusion coefficient and liquid water diffusion coefficient were obtained by numerical calculation. These calculating results were verified with Delphin software, which proved the availability of the method of testing water vapor diffusion coefficient and liquid water diffusion coefficient put forward in this paper.5. The relative humidity and the heat flux of epidermis climate layer envelope constructure were studied under rain. The new thermal insulation mortar and new ceramsite concrete were chose as epidermal layer respectively.The influence of artificial rain spraying quantity, interval and temperature on relative humidity and the heat flux were researched. And the influence of the conductivity and porosity of material on energy consumption and moisture content were studied also. The results show that the effects of using passive evaporative technology of artificial rain to reduce the energy consumption are remarkable.