Experimental Study And Analysis On Mechanism Of Coupled Heat And Moisture Transfer In Hollow Concrete Block Wall Filled With Compressed Straw Bricks

Building humid environment is not only the evaluation index of building environment,but also the key factor influencing human health,comfort,building durability and building energy consumption.The migration and accumulation of moisture in building materials is beneficial to the growth of mold,which will lead to the decrease of the indoor air quality and have a great influence on indoor air humidity and air conditioning load especially the potential cooling load.The high humidity in building envelop can cause moisture condensation and condensate,which affect the thermal performance,life and beauty of building materials.So the research of the heat and moisture transfer process in building envelop is of great significance.In this paper,research on coupled heat and moisture transfer in hollow concrete block wall filled with compressed straw bricks was carried out.A series of tests were developed based on our designed controllable coupled heat and moisture test.The experiment were divided into 4 groups according to directions of heat and moisture transfer and the variations of boundary conditions.The temperature and humidity profiles within the wall thickness through two different directions are monitored during the test.The results show:(1)Concrete straw bricks hinder temperature transfer: The curves of temperature show that the greater changes with the points closed to the higher side and the temperature curves have an obvious fluctuation at point 4 beside which the slope of the curves varies significantly.(2)The temperature gradient influence RH and moisture distribution greatly and there is strong coupling effects in heat and moisture transfer in multilayer wall: The comparison of group 1 and 2 show there is a distinct difference of each RH curved shape in group 1 while the RH curved shape in group 2 is similar with each other,the range of RH in group 1 is greater than group 2 and the moisture ratio in group 2 is lower than group 1.(3)Filling compressed straw bricks into hollow concrete block can hinder the moisture transfer in the wall: The changes of temperature and RH of environment have greater influence on moisture ratio and RH of multilayer wall in the same direction of temperature and moisture gradient.The changes of environment play a role on the wall closed to the changed time.(4)There lies a strong coupling effect in heat and moisture transfer inside the wall: the bigger the temperature difference on either side of the wall is the longer of each point reached the balanced time,the RH of environment has small influence on the moisture distribution of the wall.Our research group developed a software for simulating the coupled heat and moisture transfer in multilayer wall.Based on this software,the experiment was simulated and the comparison of the simulated results and tested results has been carried out.A good agreement was found between simulation results and tested values.The average deviation of simulated temperature and test temperature is about 0.9 ℃.The average deviation of the simulation RH and test results is about 6.8% in group 1 while the average deviation is about 11% in group 2,which is caused by the higher initial relative humidity in the tested wall.