Moisture Transfer Effects On Building Wall And Indoor Environment

The north of China is hot in summer and cold in winter,so the energy demand is large.The accurate calculation of the cooling load and the improvement of the energy multipurpose utilization ratey has become one of the urgent problems to be solved.The research on the heat transfer process of building envelop is the basis of building heating and air conditioning system design and also the foundation of building energy consumption analysis.Due to the porous,the building can effectively adjust the indoor temperature and humidity and reduce the energy consumption of air-conditioning in summer.The accurate analysis of the heat and moisture transfer in the building wall will help to understand the changes of the temperature and humidity inner the wall and its influence on the indoor parameters,and improve the building energy efficiency.In this paper,theoretical analysis,numerical simulation and experimental study are used to explore the effect of moisture transfer on the building wall and indoor environment.Through the analysis of the coupled heat and moisture transfer process inner the building wall,the paper established the heat,moisture and air coupled transfer equations relative humidity and temperature being the driving force.The lumped parameter method is used to build the indoor thermal and moisture balance equation.Regarding the building wall as a bridge,the building wall model and the indoor environment model is integrated to establish the heat and moisture coupled equation of the whole building model(HAM model).Based on the HAM model established,the finite element method is used to simulate the heat and moisture transfer process of the building wall and indoor environment.Firstly,the heat and moistre transfer process of Ji'nan typical building wall in summer was studied and this paper discussed the heat,moisture and air coupled transfer process within the common building walls and the building walls containing humidity-controlling layer.The results show that when the outdoor temperature is higher than the building wall temperature,when considering the moisture transfer,the temperature within the wall within the wall rise lower and rise rate less than that without considering moisture transfer,the latent heat of phase change accounted for a large proportion of the total heat transfer.Under the same initial condition,the moisture density value at the surface of the building wall within humidity-controlling layer value is 1.12 times than another.Moisture absorbing in the humidity-controlling layer is larger than the ordinary layer.During the 3 kinds of humidity-controlling layer that are choosed for the calculation,the moisture flow density at the inner surface of the diatomite is the biggest with the best performance.Then the effect that absorption and desorption characteristics of the building wall containing humidity-controlling layer on indoor environment are analyzed.The results show that when the temperature and humidity of the indoor environment fluctuate due to internal heat and moisture source,the absorbing of humidity-controlling materials can reduce the indoor temperature and humidity change.Variation of indoor parameters and properties of humidity-controlling materials are closely related.With the increase of thickness,the controlling capability of the humidity-controlling materials enhance,the temperature and humidity fluctuation of the indoor environment due to external disturbance is weakened.During 24 hours,when affected by the same external conditions,the indoor temperature and relative humidity increases,the indoor relative humidity value is 0.05 lower considering the humidity migration between the building wall and the indoor environment.And the temperature value is about 0.02 higher.The moisture transfer effect on the temperature and humidity of the indoor environment cannot be ignored.Finally,a temperature and humidity chamber sized 1.6m*1.6m*2m is is established to achieve precise control of indoor temperature and humidity.And temperature and humidity sensors with high precision are used within the wall at different depth and the interior space of the chamber.Temperature and humidity changes of the buildings wall and indoor environment are experimented,supporting for the corresponding basis of numerical simulation.