| The building walls are subject to the hot-humid climate with high temperature and humidity in hot summer and cold winter zone of China. The heat, air and moisture transfer within walls may severely influence the thermal performance of building envelopes, energy consumption, indoor hygrothermal environment and indoor air quality. In this dissertation, the characteristics of the coupled heat, air and moisture transfer within building walls are investigated systematically from the aspects of modeling, solution, validation and application based on the state of the art knowledge of heat and mass transfer theory in porous media in hot summer and cold winter zone of China.Firstly, a coupled heat, air and moisture transfer model which takes the heat transfer, moisture transfer, air convection and their coupled effects into consideration is developed. The relative humidity is selected as the driving potential which avoids the discontinuity problem of moisture content at the interface between two different materials and the interface between the wall surface and ambient air. Therefore, the adsorption/desorption process of wall surfaces is linked with the heat and mass transfer process within building walls which makes the analysis process easier.Secondly, a finite element based commercial software called COMSOL Multiphysics is used to solve the coupled heat, air and moisture transfer model. The air convection equation is solved independently by using Poission’s Equation model to calculate the pressure distribution which can be used to calculate the air flow through porous wall material. The known air flow will then be used in heat and moisture governing equations which should be solved simultaneously. The ―Coefficient Form PDE‖ model is selected to solve the coupled heat and moisture governing equations to obtain the temperature and moisture field across the wall.Thirdly, an experimental setup is built in Changsha to test the temperature and moisture distribution within an aerated concrete wall subjected to atmosphere condition. The measured data can be used to validate the hygrothermal model.Fourthly, the newly developed hygrothermal model is validated by comparing with the benchmark test of EN15026, HAMSTAD project and experimental data. The results show that the simulation results are in very good agreement with the results of the benchmark test of EN15026 and HAMSTAD project. The simulation results agree well with the experimental data as well. The average deviation s of relative humidity and temperature are 4.7% and 0.4oC, respectively at the interface between the lime cement plaster and aerated concrete brick(indoor side). At the interface between cement plaster and aerated concrete brick, the average deviation s of relative humidity and temperature are 3.7% and 0.93 oC, respectively(outdoor side).Finally, the effect of moisture transfer within building walls on the thermal performance of walls and energy consumption is investigated based on the newly developed hygrothermal model in hot summer and cold winter zone of China; The optimum wall insulation thickness is studied and the effect of moisture transfer within wall on optimum results is analysed; A mold control strategy and an index which estimates the risk of mold growth within walls are proposed.Hot summer and cold winter zone of China is divided into four subzones according to CDD26 and HDD18. One city is selected as the study city in each subzone. Four cities, viz. Chengdu, Shanghai, Changsha and Shaoguan, are selected. The typical exterior wall(cement plaster-red brick-lime cement plaster) commonly used in residential buildings in hot summer and cold winter zone of China is taken as the study wall. The effect of moisture transfer within building walls on the thermal performance of wall and energy consumption is investigated. The results indicate that the moisture transfer within the building envelopes in this region has a remarkable impact on building thermal and energy performance. The results are as following:(1) The peak cooling load and peak heating load are overestimated by 2.1~3.9% and 4.2~10.1%, respectively, when ignoring moisture transfer;(2) During the cooling season, the total sensible load is overestimated by 5.1~37.1% when ignoring moisture transfer;(3) The sum of the latent load accounts for 14.3~52.2% of the sum of the total load during the cooling season and the yearly latent load accounts for 4.9~6. 6% of the yearly total load when moisture transfer is taken into account;(4) The total cooling, heating and the yearly load are underestimated by 9.9~34.4%, 1.6~4.0% and 4.4~6.8%, respectively, when ignoring moisture transfer.The optimum insulation thickness of exterior wall is investigated a ccording to the lifecycle total cost analysis by considering the effect of moisture transfer within building wall on the cooling and heating energy costs. And the impact of moisture transfer within building walls on optimum results is studied. Take Chengdu, Shanghai, Changsha and Shaoguan for example, the optimum insulation thickness of commonly used brick wall using EPS as insulation material is determined. The results are as following:(1) The minimum lifecycle total cost and maximum lifecycle saving of e xterior wall using EPS as insulation are 103.10~120.87yuan/m2 and 43.12~113.74yuan/m2, respectively;(2) The optimum wall insulation thickness is 0.086~0.115m;(3) The minimum lifecycle total cost, maximum lifecycle saving and optimum insulation thickness of exterior wall using EPS as insulation are underestimated by 5.18~8.84%, 23.19~34.49% and 4.35~6.98%, respectively when ignoring moisture transfer within walls.A mold control strategy and an index which estimates the risk of mold growth within walls are proposed in order to control the growth of mold within walls. Take Chengdu, Shanghai, Changsha and Shaoguan for example, the risk of mold growth within commonly used brick walls is predicted. The results show that the risk of mold growth at the interface of different materials is the largest in Changsha, and then followed by Chengdu, Shanghai and Shaoguan. |
PDF Full Text Request