The Thermal And Humidity Characteristics Of The Wall Material And Its Influence On The Energy Consumption Of Building Heating

The moisture content of wall material will affect its thermal conductivity.However,at present,the database of thermal and wetness properties of buildi ng materials in China is quite scarce,and the thermal conductivity provided i n relevant building energy saving design standards or manuals are all the val ues in the absolutely dry state.If the influence of moisture content of material s is not considered,the thermal calculation and energy-saving design will be inconsistent with the actual situation.In order to enrich the database of therma l and wet properties of building materials in China,the thermal and wet prop erties of typical porous building materials were studied by experimental meth od.Based on this,the influence of thermal and wet properties of materials on building energy consumption is further studied.In this paper,several common porous building materials were selected an d their thermal and wet characteristics were studied,including three inorganic materials such as aerated concrete,foam concrete and ceramsite concrete,and organic materials such as straw board.Moisture transfer in porous materials is the result of evaporation diffusio n,liquid diffusion(capillary force),surface diffusion,macroscopic hydraulic fl ow and condensation.In some studies,the water content is changed by soakin g method or spraying method,which is obviously inconsistent with the engin eering practice.This paper adopts the international universal constant temperatu re and humidity chamber method to change its moisture content by adjusting the relative humidity of the environment,which is more consistent with the a ctual process of moisture transfer and moisture accumulation.According to the test,the moisture content of both organic materials and inorganic materials in creases monotonously with the increase of environmental relative humidity.Th e moisture content of the four materials in the high humidity environment inc reases by 6.25 times,4.04 times,3.6 times and 5.4 times respectively compared with the low humidity environment.After multiple fitting,it was found that polynomial fitting could accurately reflect the relationship between the balan ce moisture content of building materials and the relative humidity of the env ironment.The fitting relations of the four materials were: y = 0.00005 x3-0.0058 x2 + 0.2066 x-0.0752.Y = 0.00005 x3-0.0057 x2 + 0.2957x-0.1041;Y =0.000008x3-0.001x2 + 0.0891x-0.0404;Y =0.0001 x3-0.011 x2 + 0.4398x-0.1213.Through calculation,it is found that the four fitting curves have inflection points when the environmental relative humidity is 38.6%,38%,41.6 and 36.7% respectively.Based on the theory of steady state heat conduction,the thermal conduct ivity of wall materials under different environmental relative humidity is studi ed in this paper.It was found that the thermal conductivity of the four materi als increased with the increase of ambient relative humidity.In the high humi dity(95%)environment,the thermal conductivity increased by 51.2%,36.1%,4% and 109.6%,respectively,compared with the low humidity(30%)environ ment.The fitting relations were as follows: y = 0.0000002 x3-0.00002 x2 + 0.0007 x + 0.1207.Y = 0.0000001 x3-0.00002 x2 + 0.0007 x + 0.1187;Y = 0.00000004 x3-0.000004 x2 + 0.0001 x + 0.2129;Y = 0.0000002x3-0.00003x2 + 0.0014 x + 0.0519.It is worth noting that although aerated concrete and foamed co ncrete both belong to foamed concrete,their internal pores are connected hole s and closed holes respectively,leading to a great difference in the variation rules of their thermal conductivity.The moisture content of straw board is alw ays higher than that of the other three materials,and the moisture absorption rate in the high humidity environment is significantly higher than that of the other three materials,indicating that the moisture content of straw board is gr eatly affected by relative humidity and has a strong moisture control ability.Based on the above research,Energyplus was used to simulate the heatin g energy consumption of buildings with different moisture content of walls.Si mulation found that when the rural residential respectively using aerated concr ete,foam concrete,ceramsite concrete,straw board as wall materials,using a unique materials under dry state,to simulate the thermal physical properties o f calculation parameters and their annual heating energy consumption were 52.64 GJ,52.56 GJ,54.82 GJ,48.83 GJ,but in the use of the material thermal physical properties under high moisture environment calculation parameters is simulated,the annual heating energy consumption were 54.5 GJ,53.8 GJ,54.96 GJ,52.59 GJ.Real energy consumption increased by 3.5%,2.3%,0.3% an d 7.7%.No matter how the relative humidity of the environment changes,whe n straw board is used as the wall material,the heating energy consumption o f the building is the least.When ceramsite concrete is used as the wall materi al,the heating energy consumption of the building is the greatest,which prov es that the insulation ability of straw board is better than the other three mat erials.Both aerated concrete and foamed concrete belong to foamed concrete.Under low environmental relative humidity,the difference of heating energy c onsumption between them is small,but in high humidity environment,the dif ference is significantly increased,up to 1.2%.