Thermal Performance Evaluation And Optimal Design Of Internal Envelopes For Passive Rooms

In recent years, more and more attention has been focused on renewable energyuse for heating in buildings. Passive buildings using the direct solar radiations forheating have become more popular, especially in areas of China where fossil energysources are scarce and solar radiation plentiful, for example in the northwest part ofthe country.However, as solar energy is by nature an inconstant source of energy, passivebuildings need appliances able to stock heat in order to dampen the temperaturevariations. There are many sorts of envelope materials with heat storage properties,including constant properties ones for which thermal properties don’t vary withtemperature, and phase change materials (PCMs) which can stock large heat duringphase change range. Numerous numerical and experimental studies have been doneon the application of such materials. But most of them are based on the cases studies,whose results concern example cases and lack in generality.The main research content and results in this thesis are the following:The point model of heat storage material is built, and the thermal storagebehavior is analyzed: the temperature control behavior rule of materials is obtained,according to which, the controlling temperature perfectness is put forword to evaluatethe thermal performance of the material. To make the controlling temperatureperfectness highest, the nonlinear specific heat of the material is optimized. And theresults show that the optimal specific heat is a Dirac distribution in function oftemperature, with the characteristic temperature equal to the lower limit of thethermal comfort range and that the material’s total enthalpy must be equal to theproduct of the dissatisfaction integrated degree of equivalent outside environmentwith the area and convective heat transfer coefficient of the material point.Based on a simplified model of a passive building, we analyze and optimize thetemperature control performance of internal envelope. The optimal non-linear specificheat of internal envelope material is obtained as a function of temperature that can be approximated by a Dirac distribution. This proves that the thermal properties ofPCMs are close to the ideal thermal properties of building envelope materials, whichis helpful to use PCMs in buildings.Through this analysis of the temperature control capacity of PCMs in passivebuildings, we obtained a set of rules for an optimal design of the thermal properties ofPCMs. The rule can be used conveniently in different regions to direct the design ofPCMs. And the results show that in different regions, the optimal phase changetemperatures are close to each other.A method to estimate the advantages of using PCMs compared to using normalmaterials is put forword. It can be applied in different regions to estimate whether it isnecessary to use PCMs replace normal materials as internal envelope materials. Andit is found that, in Beijing, Shanghai, and Lhasa the advantages of using PCMs areprominent.