Study On Thermal And Humid Environment Characteristics Of Passive Humidified Earthen Dwelling House In Northwest Sichuan

In recent years,earthen materials are gaining renewed attention and use as a building material due to their temperature-regulating properties in indoor environments and their benefits to air quality,in an attempt to combine multiple aspects of safety and comfort with sustainability.Soil materials are typical porous media,based on the existing heat and humidity coupled transfer theory,and on the basis of previous studies,this paper established the soil wall heat and humidity coupled transfer model and indoor air heat and humidity balance equation of soil dwellings,which laid a foundation for the subsequent simulation of indoor heat and humidity environment of soil dwellings.Then,in order to improve the thermal and moisture parameter data of the raw soil material in the northwest of Sichuan province,this paper uses specific experimental instruments and experimental methods to determine the parameters of the material,including density,thermal conductivity,specific heat capacity,steam permeability coefficient and the hygroscopic curve equation of the material.Among them,the density and specific heat capacity of raw soil material are measured according to constant,while the thermal conductivity is measured as a function of moisture content,and the steam permeability coefficient and material hygroscopic curve are measured according to a function of relative humidity.The reason for this measurement is to make the following simulation more accurate.Next,this paper conducted wall and indoor air temperature and humidity tests in a native dwelling house located in Tielu Village,Youxian District,Mianyang City,for four days.Hourly temperature and humidity data were recorded during the four days with a specific time test instrument.Then,experimental data and analytical solutions of cases in literature are used to verify the mathematical model established above.The results show that the results of the two validation methods agree well,which verifies the correctness of the model.Then,the mathematical model is used to simulate the different working conditions of soil wall and soil dwelling.The influences of thermal conductivity and steam permeability on the thermal and moisture properties of the earth wall were compared when the thermal conductivity and steam permeability were used as functions of constant and moisture content respectively.The results show that the maximum difference of temperature curve accounts for about 14.3% of the total temperature change.The maximum difference of relative humidity is 17.1% of the total change of relative humidity,and with the passage of time,the difference has a trend of continuous increase.This means that putting in fixed parameters in the simulation calculation will inevitably increase the error of the calculation results.Then the influence of wall thickness on indoor thermal and humid environment is simulated by mathematical model.The results show that in the range of 300-700 mm wall thickness,the impact of the raw soil wall on the indoor thermal and humid environment is very small,so it is reasonable to determine the wall thickness of 370 mm.The raw material was then compared with three other common building materials.The four materials have different effects on indoor air temperature and humidity under the same working conditions.The results show that the soil material can create the best indoor thermal and humidity environment for its excellent hygroscopic ability and low steam permeability coefficient.Then the influence of different placement of insulation layer on indoor thermal and humid environment was simulated.The results show that the indoor air can be better regulated without setting moisture insulation layer on both sides of the interior and exterior,so it is the optimal condition.Then the indoor thermal and humid environment of earthen dwellings in northwest Sichuan in winter and summer is simulated.The results show that the average indoor temperature in summer is about 26.56℃,and the variance is 3.26.The average indoor relative humidity in summer is69.74%,and the variance is 43.17.The average values of wall temperature and humidity are26.92℃ and 70.41% respectively,and the variances are 3.68 and 23.92 respectively.The average indoor temperature in winter is about 7.25℃,and the variance is 1.14.The average indoor relative humidity in winter is about 83.62%,and the variance is 14.83.The average values of wall temperature and humidity are 7.39℃ and 82.42% respectively,and the variances are 1.39 and 2.75 respectively.From the simulation results,when the outdoor temperature and humidity change is severe,the raw earth wall can play a good role of buffering and protecting the indoor heat and humidity environment.In summer,86.3% of the indoor relative humidity is in the range of 60-80%.In winter,the indoor relative humidity within the range of 60-80% only accounts for 17.1% of the total time.In winter,the time at 80-90%relative humidity accounted for 82.5% of the total time.It can be seen that in summer,indoor relative humidity is in a relatively comfortable range for most of the time,compared with the indoor relative humidity in winter,it is much humid.