Testing protocols
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Michael Hurd
- WUFI User
- Posts: 103
- Joined: Thu Oct 19, 2006 5:27 am -1100
Testing protocols
I have a manufacturer of GFRC panels that seems to be willing to test his panels so we can have the data needed to input into the WUFI material database. Within the WUFI program is there any information that identifies, for each required category, the specific test criteria that needs to be used to obtain the required data? Here in the states a lot of our testing that is required follows testing methods identified by organizations such as ASTM.
Respectfully,
Michael Hurd
Michael Hurd
Dear Mr. Hurd,
WUFI is not specifically set up to use the results of particular standardized testing methods (which would be different in different countries anyway). It solves the physical transport equations for heat and moisture and thus basically needs the transport coefficients as used in these equations. Any measurement methods used to determine material parameters should be chosen so as to yield results as close as feasible, practical or necessary to these physical quantities.
In many cases, equipment and procedures prescribed by standard testing methods can be used. Sometimes the standard procedures have to be modified slightly, e.g. if measurements at more humidity levels have to be taken than prescribed by some standard.
In some cases (such as sd-values, permeances etc.) WUFI accepts not the fundamental physical quantities but alternative quantities used by building engineers; there are usually standard testing methods to determine them.
In general, measurements taken in accordance with prescribed standard test methods are used for certain legally required assessments or certifications regarding the building component or design. No such requirements exist (as yet) for numerical simulations, so you cannot be blamed for not strictly following test procedures. How to measure material parameters is largely left to the discretion of the investigator.
The hygric processes in a building material are usually not very sensitive with respect to the density, porosity and heat capacity of the materials. It may be sufficient to estimate these quantities, as discussed in the on-line help. Measurements are even better, of course, but rough values are usually sufficient and any reasonable measuring procedure will do.
Heat conductivity is usually of minor influence, too, and any standard measuring procedure will be sufficient. If a material is vapor-permeable, care should be taken in the measurements to distinguish between true heat conduction through the sample and latent heat transport by vapor diffusion with phase change within the sample.
Mu-values (or permeabilities) are usually measured with cup tests. In most cases, cup tests performed at different humidity levels (dry cup and wet cup) yield different results, due to surface diffusion superimposed on the vapor diffusion flow. Ideally, the amount of surface diffusion should be determined (by comparing the results), subtracted from the permeability and added to the liquid transport coefficients. This is rarely done, however, and WUFI allows to use the original permeability measurements for the various humidity levels. It is up to the user to decide how many measurements at different humidity levels (and at which levels) need to be made.
The moisture storage function is usually composed of sorption measurements for relative humidities below about 90% and pressure plate measurements or mercury porosimetry measurements for higher humidities. How many points on the curve need to be measured depends on the material and the situation to be investigated. If two capillary-active materials are in contact, they may draw water out of each other, and this process depends on the details in the high-moisture regions of the respective moisture storage functions which then need to be determined with sufficient resolution. If a material just absorbs or releases moisture via vapor diffusion, a much simpler moisture storage function is usually sufficient. In the simplest case, you only determine the sorption moisture at 80% RH and the free saturation and let WUFI fit a smooth curve through these two points.
Liquid transport coefficients are difficult to measure and can only be determined in dedicated laboratories. As an alternative, you may measure the water absorption coefficient ("A-value") and let WUFI estimate the liquid transport coefficients from this value.
Concrete or cement materials have the difficulty that, due to their swelling and shrinking with changing water content, their liquid transport coefficients depend not only on the current but also on previous water contents. In particular, their A-value will depend on how long the material is exposed to water. The details of this behavior can not be modeled with WUFI, and in the measurements a typical exposure time to water should be used, as is expected for the material in the component. If no appreciable absorption of liquid water (rain, condensation, ...) is to be expected, the liquid transport coefficients are not very important anyway. If liquid water uptake plays a major role in the investigated case, preliminary calculations should be done to test the sensitivity of the results with respect to these coefficients. (Such test calculations can and should always be done when the question arises how important a given material parameter is in the investigated situation and how accurately it needs to be determined.)
Regards,
Thomas
WUFI is not specifically set up to use the results of particular standardized testing methods (which would be different in different countries anyway). It solves the physical transport equations for heat and moisture and thus basically needs the transport coefficients as used in these equations. Any measurement methods used to determine material parameters should be chosen so as to yield results as close as feasible, practical or necessary to these physical quantities.
In many cases, equipment and procedures prescribed by standard testing methods can be used. Sometimes the standard procedures have to be modified slightly, e.g. if measurements at more humidity levels have to be taken than prescribed by some standard.
In some cases (such as sd-values, permeances etc.) WUFI accepts not the fundamental physical quantities but alternative quantities used by building engineers; there are usually standard testing methods to determine them.
In general, measurements taken in accordance with prescribed standard test methods are used for certain legally required assessments or certifications regarding the building component or design. No such requirements exist (as yet) for numerical simulations, so you cannot be blamed for not strictly following test procedures. How to measure material parameters is largely left to the discretion of the investigator.
The hygric processes in a building material are usually not very sensitive with respect to the density, porosity and heat capacity of the materials. It may be sufficient to estimate these quantities, as discussed in the on-line help. Measurements are even better, of course, but rough values are usually sufficient and any reasonable measuring procedure will do.
Heat conductivity is usually of minor influence, too, and any standard measuring procedure will be sufficient. If a material is vapor-permeable, care should be taken in the measurements to distinguish between true heat conduction through the sample and latent heat transport by vapor diffusion with phase change within the sample.
Mu-values (or permeabilities) are usually measured with cup tests. In most cases, cup tests performed at different humidity levels (dry cup and wet cup) yield different results, due to surface diffusion superimposed on the vapor diffusion flow. Ideally, the amount of surface diffusion should be determined (by comparing the results), subtracted from the permeability and added to the liquid transport coefficients. This is rarely done, however, and WUFI allows to use the original permeability measurements for the various humidity levels. It is up to the user to decide how many measurements at different humidity levels (and at which levels) need to be made.
The moisture storage function is usually composed of sorption measurements for relative humidities below about 90% and pressure plate measurements or mercury porosimetry measurements for higher humidities. How many points on the curve need to be measured depends on the material and the situation to be investigated. If two capillary-active materials are in contact, they may draw water out of each other, and this process depends on the details in the high-moisture regions of the respective moisture storage functions which then need to be determined with sufficient resolution. If a material just absorbs or releases moisture via vapor diffusion, a much simpler moisture storage function is usually sufficient. In the simplest case, you only determine the sorption moisture at 80% RH and the free saturation and let WUFI fit a smooth curve through these two points.
Liquid transport coefficients are difficult to measure and can only be determined in dedicated laboratories. As an alternative, you may measure the water absorption coefficient ("A-value") and let WUFI estimate the liquid transport coefficients from this value.
Concrete or cement materials have the difficulty that, due to their swelling and shrinking with changing water content, their liquid transport coefficients depend not only on the current but also on previous water contents. In particular, their A-value will depend on how long the material is exposed to water. The details of this behavior can not be modeled with WUFI, and in the measurements a typical exposure time to water should be used, as is expected for the material in the component. If no appreciable absorption of liquid water (rain, condensation, ...) is to be expected, the liquid transport coefficients are not very important anyway. If liquid water uptake plays a major role in the investigated case, preliminary calculations should be done to test the sensitivity of the results with respect to these coefficients. (Such test calculations can and should always be done when the question arises how important a given material parameter is in the investigated situation and how accurately it needs to be determined.)
Regards,
Thomas
company that provides the machine: pressure plate method
Dear Mr. Hurd,
I am student of university in Portugal, and I am currently doing a PhD about moisture storage characteristics of porous capillary active materials. When i read the document: " Determination of moisture storage characteristics of porous capillary active materials", i stayed interested about pressure plate method, then i will like to know the company that provides the machine that is used in this method, for my university to buy. I think that Fraunhofer-Institut have this machine.
It is possible for WUFI TEAM get me a contact from this company?
Regards
I am student of university in Portugal, and I am currently doing a PhD about moisture storage characteristics of porous capillary active materials. When i read the document: " Determination of moisture storage characteristics of porous capillary active materials", i stayed interested about pressure plate method, then i will like to know the company that provides the machine that is used in this method, for my university to buy. I think that Fraunhofer-Institut have this machine.
It is possible for WUFI TEAM get me a contact from this company?
Regards
Re: company that provides the machine: pressure plate method
(Question has been answered by e-mail.)jorne wrote:i will like to know the company that provides the machine that is used in this method
I would also like to have some information about the pressure plate measurement for the determination of the sorption curve.
I want to have the sorption curve of some insulation materials.
Do you realise thoses measures at the IBP? At which RH do you do your measures ? How much does it cost ?
Thank you,
I want to have the sorption curve of some insulation materials.
Do you realise thoses measures at the IBP? At which RH do you do your measures ? How much does it cost ?
Thank you,
The pressure plate measurements are not used to determine the "sorption" part of the moisture storage function. They are used to determine the moisture storage function in the "capillary moisture" region, that is, they measure the moisture content for relative humidities above 93% or so.Wirbel wrote:I would also like to have some information about the pressure plate measurement for the determination of the sorption curve.
I want to have the sorption curve of some insulation materials.
This is done by filling the material to saturation and then exposing it to increasing barometric pressures which each push a certain amount of water out of the pore system, until the internal capillary pressure in the pores is able to resist the external pressure. The amount of water pushed out at each pressure stage indicates the total volume of all pores with a given size.
I don't think you can do that with insulation materials. Once you have filled them with water, almost all of the water will have leaked out by itself even before you have started the pressure plate measurement.
You can find a description of the procedure in the thesis of M. Krus, starting on page 41:
M. Krus:
Moisture Transport and Storage Coefficients of Porous Mineral Building Materials - Theoretical Principles and New Test Methods
IRB-Verlag, 1996
http://www.ibp.fraunhofer.de/Images/mk_ ... -30730.pdf
Regards,
Thomas
Thank you Thomas for your answer.
So how do you get the moisture storage function of an insulation material ?
Especially for RH above 90%, it is difficult to obtain the curve. Although I understood it is that part of the stotage function that will impact the results of a simulation. So it is in the high relative humidity region that the moisture storage function should be as detailed as possble.
So how i can I get a detailed moisture storage function for insulation materials ?
So how do you get the moisture storage function of an insulation material ?
Especially for RH above 90%, it is difficult to obtain the curve. Although I understood it is that part of the stotage function that will impact the results of a simulation. So it is in the high relative humidity region that the moisture storage function should be as detailed as possble.
So how i can I get a detailed moisture storage function for insulation materials ?
I'm not sure whether in insulating materials that part of the moisture storage function is so much more important than the rest. It is important when capillary active materials with different moisture storage functions are in hygric contact. In that case it depends crucially on the respective moisture storage functions which material has the higher capillary tension for a given water content and thus is able to suck water out of the other material. And since capillary transport is highest at high moisture contents, it is the high end of the moisture storage function which is decisive in those cases.Wirbel wrote:Although I understood it is that part of the stotage function that will impact the results of a simulation. So it is in the high relative humidity region that the moisture storage function should be as detailed as possble.
For mineral wool however, which does not support capillary transport, this kind of influence of the moisture content on moisture transport is not present. The details of the moisture storage function will only affect the amount of moisture deposited within the mineral wool and will thus "only" have some effect on the hygric inertia of the mineral wool, the amount of water it "catches" and thus keeps away from other materials and on the moisture-dependent thermal conductivity and thermal capacity of the insulation.
We perform the usual sorption measurements which are practical only up to 95 or 97% RH. We separately measure the free saturation (based on standard DIN EN 12087: keep the sample submerged for 28 days, then let superfluous water run off over-edge for ten minutes and weigh the specimen).So how do you get the moisture storage function of an insulation material ?
Since we usually feel that a linear interpolation between 95% RH and free saturation would not be adequate (WUFI would interpolate linearly if the two table entries for 95% and free saturation were given), we fit a model function to the available sorption measurements and then tabulate the resulting curve as finely as seems useful.
The model function we usually use for this purpose is described in the thesis of A. Holm on page 37 (u is water content, uf is free saturation, pc is capillary pressure and pk1, pk2 are free parameters to be determined by the fitting process).
Regards,
Thomas