aluminium？
aluminium？
I ran into a problem in the WUFIpro simulation, where the next layer of the outer wall was a watered-down aluminum mat, but I couldn't find any metal material in the material vault. So I created a new material, but the porosity and water vapor permeability of aluminum should be close to zero, so I used standard aluminum density and thermal conductivity as well as minimal porosity and great steam resistance factor to create the new material and use it, but not simulate it. Because it has a problem with its moisture storage function, and it can't be changed to zero, and it can't be changed to a minimum value, it will indicate excess porosity or w 80 > = W saturation, in this case how can I set up to add aluminum layer of material and normal simulation. Because this layer is mainly waterproof rain so can not be ignored, I have to ask you for help with this problem. I will be very grateful to you for your answer! Looking forward to your reply.
Re: aluminium？
Hi bamboo,
if your aluminum sheet is at the surface of the building component, its only hygrothermal function will be to prevent the absorption of rain water and the exchange of vapour with the outside air. Due to its small thickness and high thermal conductivity, its effect on the thermal conditions in the component will be negligible.
In this case, the only hygrothermal function of this layer is to disable liquid transport and vapour diffusion between the environment and the building component, and you can reach the same effect if you replace this layer with an appropriate choice of the surface transfer coefficients.
To do this, do not include any aluminum sheet as a layer in the component assembly (so that the layer below the aluminum will now be the outermost layer of the simulated component). Instead, switch rain absorption off by setting the "Adhering fraction of rain" to zero. And switch vapour exchange off by setting the "sd-Value" at the exterior surface to a very large number, for example 9e9.
In this way, the surface transfer coefficients are modelling the hygrothermal effect of the aluminum sheet, so that the sheet does not need to be modelled as a layer in the component.
Of course, the short-wave radiation absorptivity of the component should be set to the value of aluminum to simulate the correct amount of absorbed solar radiation.
----
If you prefer not to follow this recommendation and instead insist on including an aluminum layer explicitly in the assembly, please keep in mind that WUFI has been developed to simulate the heat and moisture transport in porous materials. This kind of material always has a moisture storage function which is not zero. This is why you have to include a non-zero moisture storage function in all simulated materials, even if in reality they cannot contain any moisture, such as the aluminum sheet. You should then define a very low moisture storage function, so that the small amount of moisture contained in the simulated material does not change the moisture behavior of the material as a whole.
Since this moisture content is artificial anyway, you can use an artificial (that is, not necessarily realistic) moisture storage function. For example, you may use the simple table
0 0
1 1
which says that at relative humidity = 0 the water content is = 0 kg/m³ (as usual) and that at relative humidity = 1 (=100 %) the water content is 1 kg/m³. The number for the moisture content at 100 % RH should be chosen as small as possible, but if it is too small, WUFI's numerical procedures will have problems, so you will have to experiment a little bit to find a suitable number. The porosity of the material must be chosen so that 1000*porosity is greater than the number chosen for the moisture content at 100 % RH, otherwise WUFI will report an error.
The Water Vapour Diffusion Resistance Factor of the material should be set to a very large number (fort example 9e9) because there can be no vapour diffusion in aluminum. The Liquid Transport Coefficients should be set to zero because there can be no liquid transport in aluminum.
Of course the water content of the aluminum reported in the simulation results should be ignored.
Regards,
Thomas
if your aluminum sheet is at the surface of the building component, its only hygrothermal function will be to prevent the absorption of rain water and the exchange of vapour with the outside air. Due to its small thickness and high thermal conductivity, its effect on the thermal conditions in the component will be negligible.
In this case, the only hygrothermal function of this layer is to disable liquid transport and vapour diffusion between the environment and the building component, and you can reach the same effect if you replace this layer with an appropriate choice of the surface transfer coefficients.
To do this, do not include any aluminum sheet as a layer in the component assembly (so that the layer below the aluminum will now be the outermost layer of the simulated component). Instead, switch rain absorption off by setting the "Adhering fraction of rain" to zero. And switch vapour exchange off by setting the "sd-Value" at the exterior surface to a very large number, for example 9e9.
In this way, the surface transfer coefficients are modelling the hygrothermal effect of the aluminum sheet, so that the sheet does not need to be modelled as a layer in the component.
Of course, the short-wave radiation absorptivity of the component should be set to the value of aluminum to simulate the correct amount of absorbed solar radiation.
----
If you prefer not to follow this recommendation and instead insist on including an aluminum layer explicitly in the assembly, please keep in mind that WUFI has been developed to simulate the heat and moisture transport in porous materials. This kind of material always has a moisture storage function which is not zero. This is why you have to include a non-zero moisture storage function in all simulated materials, even if in reality they cannot contain any moisture, such as the aluminum sheet. You should then define a very low moisture storage function, so that the small amount of moisture contained in the simulated material does not change the moisture behavior of the material as a whole.
Since this moisture content is artificial anyway, you can use an artificial (that is, not necessarily realistic) moisture storage function. For example, you may use the simple table
0 0
1 1
which says that at relative humidity = 0 the water content is = 0 kg/m³ (as usual) and that at relative humidity = 1 (=100 %) the water content is 1 kg/m³. The number for the moisture content at 100 % RH should be chosen as small as possible, but if it is too small, WUFI's numerical procedures will have problems, so you will have to experiment a little bit to find a suitable number. The porosity of the material must be chosen so that 1000*porosity is greater than the number chosen for the moisture content at 100 % RH, otherwise WUFI will report an error.
The Water Vapour Diffusion Resistance Factor of the material should be set to a very large number (fort example 9e9) because there can be no vapour diffusion in aluminum. The Liquid Transport Coefficients should be set to zero because there can be no liquid transport in aluminum.
Of course the water content of the aluminum reported in the simulation results should be ignored.
Regards,
Thomas