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# [[FAQ_General:SourcesofMaterialData | <B>Sources of Material Data</B>]]  
# [[FAQ:General:SourcesofMaterialData | <B>Sources of Material Data</B>]]  
# [[FAQ_General:SourcesofClimateData | <B>Sources of Climate Data</B>]]  
# [[FAQ:General:SourcesofClimateData | <B>Sources of Climate Data</B>]]  
# [[FAQ_General:VolumePercent,MassPercent | <B>Volume Percent, Mass Percent</B>]]
# [[FAQ:General:VolumePercent,MassPercent | <B>Volume Percent, Mass Percent</B>]]
# [[FAQ_General:RelativeHumidityinaBuildingComponent | <B>Relative Humidity in a Building Component</B>]]
# [[FAQ:General:RelativeHumidityinaBuildingComponent | <B>Relative Humidity in a Building Component</B>]]
# [[FAQ_General:DefaultMoistureStorageFunction | <B>Default Moisture Storage Function</B>]]
# [[FAQ:General:DefaultMoistureStorageFunction | <B>Default Moisture Storage Function</B>]]
# [[FAQ_General:WaterContentofanAirLayer | <B>Water Content of an Air Layer</B>]]
# [[FAQ:General:WaterContentofanAirLayer | <B>Water Content of an Air Layer</B>]]
# [[FAQ_General:ConvergenceFailureCausedbyVapor-PermeableLayer | <B>Convergence Failure Caused by Vapor-Permeable Layer</B>]]
# [[FAQ:General:ConvergenceFailureCausedbyVapor-PermeableLayer | <B>Convergence Failure Caused by Vapor-Permeable Layer</B>]]
# [[FAQ_General:MoistureContentataMonitoringPosition | <B>Moisture Content at a Monitoring Position</B>]]
# [[FAQ:General:MoistureContentataMonitoringPosition | <B>Moisture Content at a Monitoring Position</B>]]
# [[FAQ_General:LiquidTransportCoefficentofaPaintLayer | '''Liquid Transport Coefficient of a Paint Layer''']]
# [[FAQ:General:LiquidTransportCoefficentofaPaintLayer | '''Liquid Transport Coefficient of a Paint Layer''']]
# [[FAQ_General:RainAbsorptionFactorofanUnrenderedSandstoneWall | '''Rain Absorption Factor of an Unrendered Sandstone Wall''']]
# [[FAQ:General:RainAbsorptionFactorofanUnrenderedSandstoneWall | '''Rain Absorption Factor of an Unrendered Sandstone Wall''']]
# [[FAQ_General:HygricParametersofEcologicalInsulationMaterials | <B>Hygric Parameters of Ecological Insulation Materials</B>]]
# [[FAQ:General:HygricParametersofEcologicalInsulationMaterials | <B>Hygric Parameters of Ecological Insulation Materials</B>]]
# [[FAQ_General:TypicalInitialMoistureContent | <B>Typical Initial Moisture Content</B>]]
# [[FAQ:General:TypicalInitialMoistureContent | <B>Typical Initial Moisture Content</B>]]
# [[FAQ_General:WaterRepellentFacade | <B>Water-Repellent Facade</B>]]
# [[FAQ:General:WaterRepellentFacade | <B>Water-Repellent Facade</B>]]
# [[FAQ_General:SimulationofAbsorptionExperiment | <B>Simulation of Absorption Experiment</B>]]
# [[FAQ:General:SimulationofAbsorptionExperiment | <B>Simulation of Absorption Experiment</B>]]
# [[FAQ_General:AbsorptionExperimentwithLimitedWaterSupply | '''Absorption Experiment with Limited Water Supply''']]
# [[FAQ:General:AbsorptionExperimentwithLimitedWaterSupply | '''Absorption Experiment with Limited Water Supply''']]
# [[FAQ_General:WhyNever100RHintheComponent | '''Why Never 100% RH in the Component?''']]
# [[FAQ:General:WhyNever100RHintheComponent | '''Why Never 100% RH in the Component?''']]
#[[FAQ_General:100RHattheFacade | 100% RH at the Facade''']]
# [[FAQ:General:100RHattheFacade | '''100% RH at the Facade''']]
# [[FAQ_General:CriteriaforEvaluatingHygrothermalPerformance | '''Criteria for Evaluating Hygrothermal Performance''']]
# [[FAQ:General:CriteriaforEvaluatingHygrothermalPerformance | '''Criteria for Evaluating Hygrothermal Performance''']]
# [[FAQ_General:VentilatedCurtainWalls | '''Ventilated Curtain Walls''']]
# [[FAQ:General:VentilatedCurtainWalls | '''Ventilated Curtain Walls''']]
# [[FAQ_General:HeatFlowThroughExteriorSurfaceIsNotRealistic | '''Heat Flow Through Exterior Surface Is Not Realistic?''']]
# [[FAQ:General:HeatFlowThroughExteriorSurfaceIsNotRealistic | '''Heat Flow Through Exterior Surface Is Not Realistic?''']]
# [[FAQ_General:MoreRecentWeatherData | '''More Recent Weather Data?''']]
# [[FAQ:General:MoreRecentWeatherData | '''More Recent Weather Data?''']]
# [[FAQ_General:AveragingofConductivitiesatElementBoundaries | '''Averaging of Conductivities at Element Boundaries''']]
# [[FAQ:General:AveragingofConductivitiesatElementBoundaries | '''Averaging of Conductivities at Element Boundaries''']]
# [[FAQ_General:ConversationofRadiationDataforOtherDirections | '''Conversion of Radiation Data for Other Directions''']]
# [[FAQ:General:ConversationofRadiationDataforOtherDirections | '''Conversion of Radiation Data for Other Directions''']]
 
 
<P>
<B><A NAME="01">(1):</A></B><BR>
<B>Where can I find material data for materials which are not included in the
database?</B>
</P>
<P>
Unfortunately, finding material data for hygric simulations can prove difficult since
there are no standard collections of such data as yet. While thermal data can be found
in many books, hygric data are sparse and hard to come by.
</P>
<P>
A collection of design values for <A HREF="BasicMaterialData.htm">heat conductivity</A>
(including the effect of practical moisture content) and
<A HREF="BasicMaterialData.htm">diffusion resistance factors</A>
is listed in German standard DIN 4108-4
and numerous textbooks on building physics. The new DIN EN 12524 lists thermal as well
as basic hygric design values for building materials.
</P>
<P>
An extensive list of "NIST Heat Transmission Properties of Insulating and Building
Materials" is available on-line at <A HREF="http://srdata.nist.gov/insulation/">http://srdata.nist.gov/insulation/</A>.
</P>
<P>
<A HREF="MoistureStorageFunction.htm">Moisture storage functions</A> and
<A HREF="LiquidTransportCoefficients.htm">liquid transport coefficients</A> may
be estimated from the
standard parameters
<A HREF="MoistureStorageFunction.htm">w<small>f</small>, w<small>80</small></A> and the
<A HREF="LiquidTransportCoefficients.htm">A-value</A> which may
also be found in some textbooks (at least for selected materials) and data sheets or
can be measured relatively easily.
</P>
<P>
Occasionally, some data may be found scattered through the specialised literature,
but there is no systematic way to retrieve them.
</P>
<P>
Sometimes the manufacturer may be able to provide material data. Some laboratories
(including IBP) can measure the required data if samples are provided.
</P>
 
<P>
<B><A NAME="02">(2):</A></B><BR>
<B>Where can I find climate data?</B>
</P>
<P>
Hourly climate data which include rain are even harder to find than material data.
</P>
<P>
IBP offers one year of hourly weather data with WUFI (the file can also be downloaded from
the IBP website). These data from 1991 are considered fairly representative for the
climate of the Holzkirchen region.<BR>
In addition, weather data for 93 locations in Europe, America and Japan are provided
with the professional WUFI version.
</P>
<P>
Another source of hourly weather data for Germany are the Test Reference Years of the German Meteorological Service DWD which represent typical as well as extreme weather situations.
Since they are primarily intended for heating and energy consumption investigations, they
have no rain data, however, and thus are of only limited usefulness for hygrothermal
investigations.
</P>
<P>
For other possible climate data sources see <A HREF="SourcesForClimateData.htm">Sources
for Climate Data</A>.
</P>
<P>
If the situation of a specific object is to be investigated, it may be necessary to measure
the weather in-situ anyway.
</P>
 
 
<P>
<B><A NAME="03">(3):</A></B>
<B>WUFI gives me the water content of the simulated wall in units of kg/m&sup3; or in
volume percent. However, I need the result in mass percent. How do I convert the
results?</B><BR>
</P>
 
<P>
WUFI usually gives the water content as "water density", i.e. how many kg of water are
in one m&sup3; of building material.<BR>
A result given in volume percent tells you how many m&sup3; of water are in one m&sup3; of
building material (expressed as percentage).<BR>
A result given in mass percent tells you how many kg of water are in one kg of dry
building material (expressed as percentage). Please note that the water content in
mass percent may easily exceed 100% if the dry material has low density.
</P>
 
<P>
With
</P>
<TABLE>
<TR><TD><TT>m_W</TT> :</TD><TD>mass of the water in the component</TD></TR>
<TR><TD><TT>r_W</TT> :</TD><TD>density of water (= 1000 kg/m&sup3;)</TD></TR>
<TR><TD><TT>V_W</TT> :</TD><TD>volume of the water in the component</TD></TR>
<TR><TD><TT>m_C</TT> :</TD><TD>mass of the component</TD></TR>
<TR><TD><TT>r_C</TT> :</TD><TD>density of the (dry) component</TD></TR>
<TR><TD><TT>V_C</TT> :</TD><TD>volume of the component</TD></TR>
</TABLE>
<P>
we have
</P>
<TABLE>
<TR><TD COLSPAN="3">water content as expressed by WUFI:</TD></TR>
 
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
 
<TR><TD>&nbsp;</TD><TD><TT>u</TT></TD><TD><TT>= m_W / V_C  [kg/m&sup3;]</TT></TD></TR>
 
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
 
<TR><TD COLSPAN="3">water content expressed in volume percent:</TD></TR>
 
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
 
<TR><TD>&nbsp;</TD><TD><TT>u_v</TT></TD><TD><TT>= V_W / V_C * 100</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= (m_W / r_W) / V_C * 100</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= (m_W / V_C) / r_W * 100</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= u * 100 / r_W</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= u * 100 / 1000</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= u / 10</TT></TD></TR>
 
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
 
<TR><TD COLSPAN="3">water content expressed in mass percent:</TD></TR>
 
<TR><TD>&nbsp;</TD><TD><TT>u_m</TT></TD><TD><TT>= m_W / m_C * 100</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= m_W / (r_C * V_C ) * 100</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= (m_W / V_C) * (100 / r_C)</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= u * (100 / r_C)</TT></TD></TR>
 
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD><TT>= u / (r_C / 100)</TT></TD></TR>
</TABLE>
<P>
So you get the water content in volume percent if you divide the
WUFI result [kg/m&sup3;] by <TT>10</TT>.<BR>
You get the water content in mass percent if you divide the WUFI
result by <TT>(density of the building component / 100)</TT>.
</P>
 
<P>
<B><A NAME="04">(4):</A></B><BR>
<B>I'm trying to make sense of the WUFI results, but I'm confused. What exactly is
'relative humidity' and what is the relative humidity in a building component
referred to?</B><BR>
</P>
<P>
In air the relative humidity is the ratio of the actual water vapor partial pressure
p and the water vapor saturation pressure p<small>s</small>. Example: If the air
temperature is 20°C (and therefore p<small>s</small> = 2340 Pa) and the actual
vapor pressure is 1872 Pa, then the relative humidity is 1872 Pa / 2340 Pa = 0.8 = 80%.
</P>
<P>
The condition in a porous building material corresponds to a RH of x % if it has been
exposed to air with a RH of x % until equilibrium was reached and no moisture was taken
up or given off any more.<BR>
The moisture in the material is then in equilibrium with the RH of the air in the
pore spaces. At RHs less than ca. 50% this means that a molecular layer with a
thickness of one or a few molecules has been adsorbed at the surfaces of the pores;
at higher RHs capillary condensation occurs.
</P>
<P>
Here is what happens in detail: the usual formulas for the saturation vapor pressure
(such as in German standard DIN 4108) are only valid for plane water surfaces. At
concavely curved surfaces, where the water molecules are bound stronger, the saturation
vapor pressure is reduced; the more so the stronger the curvature of the surface is.
</P>
<P>
In a partly filled capillary the interface surface between air and water forms
a curved meniscus whose curvature is determined by the surface energies involved
and in particular by the radius of the capillary. If the air space in such a
capillary is filled with air whose partial water vapor pressure is greater than the
saturation vapor pressure at the meniscus (whereas the RH in the air is still less than
100%), then the air in the immediate neighborhood of the meniscus is supersaturated
and water condenses from the air onto the meniscus, i.e. the capillary fills up.
</P>
<P>
In a porous material there exists a wide range of pore sizes. In the smallest pores,
any menisci may be curved so strongly that in these pores moisture condenses onto
the menisci from 50% RH in the pore air upwards. The smallest pores get filled
with water, and subsequently larger and larger pores (with smaller curvatures of
the menisci) get filled until a pore size is reached where - because of the larger
pore size and the smaller curvature of the meniscus - the saturation vapor pressure
at the meniscus is equal to the vapor pressure in the pore air. In this way capillary
condensation results in an equilibrium between the moisture content and the relative
humidity in the pore air, even if this RH is less than 100%. The amount of water needed
to fill the pores up to this point depends on the pore structure and the pore
size distribution.
</P>
<P>
The <A HREF="MoistureStorageFunction.htm">moisture storage function</A> describes the
amount of moisture taken up in this manner by the building material if it is exposed
to air with a specific RH. Since this relationship between RH and moisture content
is largely temperature-independent, the RH is an important and unique parameter
describing the moisture content of a material.
</P>
 
<P>
<B><A NAME="05">(5):</A></B><BR>
<B>When I do not define a moisture storage function for a material, WUFI uses
a default moisture storage function instead. What does this function look like?</B>
</P>
<P>
WUFI needs a well-defined moisture field for each time step, so it must assign a
moisture content even to materials which nominally don't have any appreciable
moisture content (e.g. water-repellent mineral wool, air layers etc.).
</P>
<P>
The default <A HREF="MoistureStorageFunction.htm">moisture storage function</A> used
by WUFI is described by the function<BR>
 
<TABLE>
<TR><TD COLSPAN="3"><TT>w = a / (b - phi) + c</TT></TD></TR>
<TR><TD><TT>w</TT></TD><TD ALIGN="RIGHT">[kg/m&sup3;]:</TD><TD>water content </TD></TR>
<TR><TD><TT>phi</TT></TD><TD ALIGN="RIGHT">[-]:</TD><TD>relative humidity</TD></TR>
</TABLE>
</P>
<P>
Since <TT>phi</TT> must be 0 for <TT>w=0</TT>, it follows immediately that<BR>
&nbsp;<TT>c = -a/b</TT><BR>
&nbsp;<BR>
The constants <TT>a</TT> and <TT>b</TT> are determined as follows:<BR>
&nbsp;<BR>
<TT>b</TT> is set to 1.0105.<BR>
&nbsp;<BR>
The moisture content at free saturation, w<small>f</small>, corresponds to
a relative humidity of 1 (=100%). Since WUFI also needs a unique relationship
between moisture content and RH for moisture contents above free saturation, this
oversaturation region is assigned RHs greater than 1, up to
<TT>phi<small>max</small> = 1.01</TT>. This value
<TT>phi<small>max</small></TT> is
reached when the moisture content reaches maximum saturation
<TT>w<small>max</small></TT> which is
determined by the <A HREF="BasicMaterialData.htm">porosity</A>:<BR>
&nbsp;<BR>
&nbsp;<TT>w<small>max</small> = porosity * 1000 kg/m&sup3;</TT><BR>
&nbsp;<BR>
Therefore we have<BR>
&nbsp;<BR>
&nbsp;<TT>w<small>max</small> = a / (b-phi<small>max</small>) - a/b.</TT><BR>
&nbsp;<BR>
Solving for <TT>a</TT> yields:<BR>
&nbsp;<BR>
&nbsp;<TT>a = w<small>max</small> * b * (b - phi<small>max</small>) /
  phi<small>max</small></TT>,<BR>
&nbsp;<BR>
and thus:<BR>
&nbsp;<BR>
&nbsp;<TT>w / w<small>max</small> = phi / (b - phi) * (b - phi<small>max</small>)
/ phi<small>max</small></TT>.<BR>
&nbsp;<BR>
&nbsp;<BR>
In particular, for <TT>phi=1</TT> we have<BR>
&nbsp;<BR>
&nbsp;<TT>w<small>f</small> / w<small>max</small> = 1 / (b - 1) *
(b - phi<small>max</small>) / phi<small>max</small> = 0.047</TT>.<BR>
&nbsp;<BR>
So this pseudo material has a free saturation of <TT>w<small>f</small> = 0.047 w<small>max</small></TT>.
</P>
<P>
<IMG SRC="pix/e_defaultfspfkt.gif" WIDTH="500" HEIGHT="246" VSPACE="0" HSPACE="0" ALT="">
</P>
 
<P>
<B><A NAME="06">(6):</A></B><BR>
<B>I did a WUFI calculation with an assembly that includes an air layer. However, I get
completely unrealistic water contents for the air layer. What went wrong?</B>
</P>
<P>
WUFI was developed to simulate the hygrothermal processes in porous building
materials. The detailed simulation of heat and moisture transport in air layers
(including convection, turbulence etc.) is much more complicated and is outside
WUFI's scope. Furthermore, it does not make much sense to try and implement these
inherently two- or three-dimensional processes in a one-dimensional simulation program.
</P>
<P>
<A HREF="AirLayers.htm">Air layers</A> can therefore only approximately be
simulated by treating them as a 'porous' material. It is possible to allow
for the amplifying effect of convection on heat and moisture transport by
employing appropriate effective
<A HREF="BasicMaterialData.htm">heat conductivities</A> and
<A HREF="BasicMaterialData.htm">vapor diffusion resistance factors</A>.
</P>
<P>
However, the <A HREF="MoistureStorageFunction.htm">moisture storage function</A> of
an air layer can only very crudely be approximated by the moisture storage
function of a porous material. The latter is largely temperature-independent
(and implemented as such in WUFI), so that the functional dependence of the
moisture content in air on the relative humidity <I>and temperature</I> cannot be
reproduced.<BR>
Furthermore, the default moisture storage function used by WUFI for materials
for which the user has not defined one assumes that capillary condensation will
occur in the material already at relative humidities less than 100%, which is
not true for an air layer (it has been modeled after the moisture contents of
dense mineral wool).
</P>
<P>
As a result you will get unrealistically large moisture contents for air layers.
Note, however, that WUFI uses the <I>relative humidity</I> as the driving potential
for moisture transport and computes the <I>water content</I> as a <I>secondary</I>
quantity from the resulting relative humidity (using the moisture storage function
of the respective material).<BR>
So the resulting distribution of <I>relative humidity</I> should in general be quite
realistic, its temporal behavior will just be damped much more than in reality
(the moisture content acts as a 'capacity term' for moisture transport in the
same way the heat capacity acts as a capacity term for heat transport). If
short-term fluctuations don't play a major role, the general trend in the
behavior of the relative humidity should be tolerably realistic.<BR>
This also means that quantities that depend on the relative humidity in or
near the air layer (e.g. mould growth rates) can be evaluated more
realistically than quantities that primarily depend on the moisture content
(e.g. heat conductivity, heat capacity).
</P>
<P>
Please note that the unrealistically large moisture capacity of an air layer
may also affect other layers. If you are interested in the moisture
distribution in an assembly that contains an air layer, the air may (or may
not) take up more moisture than realistic, so that less moisture remains for
distribution among the other layers.
</P>
<P>
You may mitigate these problems by explicitly defining a slightly more realistic
moisture storage function for the air layer. To this end, use a linear function
like
</P>
<TABLE>
<TR><TD><TT>phi:&nbsp;</TT></TD><TD><TT>w:              </TT></TD></TR>
<TR><TD><TT>0        </TT></TD><TD><TT>0                </TT></TD></TR>
<TR><TD><TT>1        </TT></TD><TD><TT>w<small>f</small></TT></TD></TR>
</TABLE>
<P>
with a low value for w<small>f</small> (the numerics may not be able to cope with
very low values, you'll need to experiment a bit) (*). This avoids the spurious
capillary condensation.
</P>
<P>
Also see the next question for a related problem.
</P>
<P>
(*) Note, however, that the porosity and thus w<small>max</small> should
remain high. If the water content exceeds w<small>f</small>, WUFI reduces
the vapor permeability, in proportion to the excess, to reflect the fact that
the pore volume gets increasingly filled with water and thus vapor transport
decreases. At w=w<small>max</small> the permeability reaches zero (all pores
are filled). For vapor-permeable materials like air layers or mineral wool
where moisture transport occurs mainly via vapor transport, w<small>max</small>
should therefore remain at a realistic value.
</P>
 
<P>
<B><A NAME="07">(7):</A></B><BR>
<B>I tried to perform a WUFI simulation, but the water balance never adds up,
regardless whether I make the grid as fine as possible or whether I choose
stricter numerical parameters, as suggested in the on-line help. What can I do?</B>
</P>
<P>
One situation where serious convergence failures tend to occur is a component
with a vapor-permeable layer (e.g. air or mineral wool) which has accumulated
a lot of moisture (RH &#126; 100%) and which is now exposed to a high temperature
gradient (e.g. caused by intense solar radiation). WUFI originally wasn't
developed to treat these cases which sometimes prove too demanding for the
numerics that are mainly tuned to massive porous materials.
</P>
<P>
<IMG SRC="pix/e_konvf_hivlt.gif" WIDTH="300" HEIGHT="300" VSPACE="0" HSPACE="0" ALT="">
</P>
<P>
If everything else fails, you may try an alternative
<A HREF="MoistureStorageFunction.htm">moisture storage function</A>.
In the material database, the moisture storage functions for materials like
air or mineral wool are left undefined, so that WUFI uses an internally defined
default moisture storage function (see the preceding two questions).
</P>
<P>
This moisture storage function assumes that for RHs above ca. 50% capillary
condensation occurs which leads to increasingly higher moisture contents until
free saturation is reached at 100% RH. This is not really realistic for air
layers or hydrophobic mineral wool (it may be more appropriate for
non-hydrophobic mineral wool).<BR>
Since it seems that the problem is mainly caused by the high water content,
reduction of the water content by choosing a different moisture storage
function often remedies the problem.<BR>
Please note that the <I>relative humidity</I> in the material will remain largely
unaffected by the specific choice of the moisture storage function, as explained
above. So if you are interested in the relative humidity in the layer, your results
will be affected only slightly (but please perform a few test calculations with
different choices of the moisture storage function to be sure), and if you are
interested in the moisture content, you should not rely on the default moisture
storage function anyway, but use measured data instead which represent your
particular material.
</P>
<P>
A possible choice for the moisture storage function in these cases is a
table like this:
</P>
<TABLE>
<TR><TD><TT>phi:&nbsp;</TT></TD><TD><TT>w:              </TT></TD><TR>
<TR><TD><TT>0        </TT></TD><TD><TT>0                </TT></TD></TR>
<TR><TD><TT>1        </TT></TD><TD><TT>w<small>f</small></TT></TD></TR>
</TABLE>
<P>
Use a low value for w<small>f</small> (the numerics may not be able to cope
with very low values, you'll need to experiment a bit.) (*).<BR>
This linear function is even more realistic than the default function in
that it avoids the capillary condensation for RH= 50..100%. The moisture content
remains low up to RH=100% (as it should be in air or in hydrophobic insulation
materials), and at or above 100% condensation may occur and increase the
moisture content beyond w<small>f</small> and up to w<small>max</small>.
</P>
<P>
In particular if you are interested in moisture accumulation by condensation in
these materials, use such a linear moisture storage function with low
w<small>f</small>. Then you know that any moisture content exceeding
w<small>f</small> must have been caused by condensation. You can then analyse
this excess over w<small>f</small> (test calculations show that this excess is
only slightly dependent on the specific choice of w<small>f</small>).
</P>
<P>
(*) Note, however, that the porosity and thus wmax should remain high. If the
water content exceeds w<small>f</small>, WUFI reduces the vapor permeability,
in proportion to the excess, to reflect the fact that the pore volume gets
increasingly filled with water and thus vapor transport decreases. At
w=w<small>max</small> the permeability reaches zero (all pores are filled).
For vapor-permeable materials like air layers or mineral wool where moisture
transport occurs mainly via vapor transport, wmax should therefore remain at a
realistic value.
</P>
 
<P>
<B><A NAME="08">(8):</A></B><BR>
<B>How can I get the moisture content at a monitoring position?</B>
</P>
<P>
WUFI's output includes the temporal behavior of
</P>
<UL>
  <LI>temperature and relative humidity at the monitoring positions, and of</LI>
  <LI>the mean moisture content of each layer.</LI>
</UL>
<P>
In order to get the <I>moisture content</I> at a <I>monitoring position</I>, you
can either
</P>
<UL>
  <LI>calculate it from the relative humidity prevalent at that monitoring
      position by means of the
      <A HREF="MoistureStorageFunction.htm">moisture storage function</A>, or</LI>
  <LI>insert a thin 'diagnostic' layer at the position in question which has
      the same material properties as the surrounding material. WUFI will
      output curves for the water contents of each layer, including a separate
      curve for the diagnostic layer. This is also a useful way to get the water
      content of, say, the outermost 5 cm of a layer.</LI>
</UL>
 
<P>
<B><A NAME="09">(9):</A></B><BR>
<B>I want to examine the effect of driving rain on a painted wall. What liquid
transport coefficients D<small>ws</small> do I enter for the paint?</B>
</P>
<P>
There are no measurements of <A HREF="LiquidTransportCoefficients.htm">transport
coefficients</A> or, equivalently, water absorption coefficients for paint layers
themselves known to us.
</P>
<P>
What is measured sometimes is the water uptake for different paint layers by applying
the paint on a standard substrate (such as cellular concrete or lime cement mortar)
and measuring the water absorption for this composite material.
</P>
<P>
So the best thing you can do is probably the following:<BR>
Don't use a layer of rendering and a layer of paint; instead, use a layer of the 'hybrid'
material for which you already know the combined water uptake from the measurements.
Use the D<small>ws</small> from the hybrid water uptake (let it generate by WUFI from the
measured water absorption coefficient) and use the D<small>ww</small> and other data from
the original rendering.
</P>
<P>
The <A HREF="WaterVaporDiffusion.htm">vapor diffusion resistance</A> of the paint
can then be included in the <A HREF="DialogEditSurfaceCoefficients.htm">surface
transfer coefficients</A> (as long as it is not markedly moisture-dependent).
</P>
<P>
Please note some possible problems, though:
</P>
<UL>
  <LI>The result of the measurement may (or may not) depend on the substrate material,
      the details of the application etc. So you should make sure that you are using
      a water absorption value that has been measured under the same circumstances
      as the case you consider in your calculations.<LI>
  <LI>The paint may slowly change its properties when it gets wet (e.g. by swelling).
      The mean properties over a rain period of two or three hours may be different
      than the mean properties during a measurement that takes many hours. Again,
      the measurement should be done close to natural conditions.</LI>
</UL>
 
<P>
<B><A NAME="10">(10):</A></B><BR>
<B>What is the right choice for the rain absorption factor for an unrendered natural
sandstone wall? When I use the value of 0.7 suggested by WUFI, then the entire wall gets
wet like a sponge. When I reduce the absorption factor to 0.5, the same happens, it just
takes longer. What's wrong?</B>
</P>
<P>
This should not happen, but the
<A HREF="RainWaterAbsorptionFactor.htm">rain absorption factor</A> is very likely not to
blame. It does not depend on the material of the wall (it depends a bit on its surface
structure and, of course, on its tilt). After all, it simply expresses the fact that
some of the rain water splashes off when it hits the wall surface and is no longer
available for absorption.
</P>
<P>
Are you sure that the amount of rain is okay? Maybe you created your own *.KLI file and
used normal rain instead of the correct driving rain?<BR>
Several kinds of sandstone have a very high water absorption (e.g. Rüthener) and may
accumulate an inacceptable amount of moisture when exposed to a wet climate such as
the Holzkirchen weather. Maybe you used one of those?
</P>
 
<P>
<B><A NAME="11">(11):</A></B><BR>
<B>I want to investigate the hygric behavior of ecological insulation materials,
such as flax, hemp or reed. However, these materials consist of fibres, whereas WUFI
is mainly designed for capillary-active porous materials. What is the best approach?</B>
</P>
<P>
The difference between fibres and porous mineral materials is in general not really
crucial for the transport equations. The fibre materials may tend to have preferred
transport directions, which would have to be allowed for by using appropriate material
data for the x and y directions in a two-dimensional calculation.
</P>
<P>
Determining the
<A HREF="LiquidTransportCoefficients.htm">liquid transport coefficients</A>, however,
may be difficult or even impossible if they change their consistency upon wetting
(e.g. by caking).
</P>
<P>
On the other hand:<BR>
As long as your insulation materials don't become so wet that capillary conduction
becomes predominant, you can ignore capillary transport and only consider diffusion
transport. That is, you leave the liquid transport coefficients undefined and
only enter a
<A HREF="BasicMaterialData.htm">&micro;-value</A>. Surface diffusion phenomena
may be allowed for by using a
<A HREF="DiffusionResistanceFactorMoistureDependent.htm">moisture-dependent
&micro;-value</A>.
</P>
<P>
Since you probably only want to assess <I>whether or not</I> the insulation becomes
wet by rain or condensation, you will mainly be concerned with water contents in the
sorption moisture region of the
<A HREF="MoistureStoragefunction.htm">moisture storage function</A>, for which these
simplifications should be adequate.<BR>
As these materials must be prevented from becoming wetted through anyway, there
will be no need to investigate in detail the behavior of an insulation soaked
full of water.
</P>
 
 
<P>
<B><A NAME="12">(12):</A></B><BR>
<B>I want to find out how long it takes a wall with construction moisture to dry
out. Which initial moisture content should I use?</B>
</P>
<P>
That depends on a number of individual circumstances such as the amount of production
moisture (e.g. in cellular concrete or lime silica bricks), the amount of mixing water
(in concrete or mortar), the amount of rain hitting the wall while it was unrendered,
the season when construction took place (warm/cold) etc., so no general answer is
possible here. The table gives examples for typical initial moisture contents:
</P>
 
<TABLE>
<TR><TD COLSPAN="2" ALIGN="CENTER"><B>Material</B></TD><TD ALIGN="CENTER"><B>Water content [kg/m&sup3;]</B></TD></TR>
<TR><TD COLSPAN="3"><B>Fresh concrete:</B></TD></TR>
<TR><TD>&nbsp;</TD><TD>free water</TD><TD ALIGN="CENTER">175</TD></TR>
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
<TR><TD COLSPAN="3"><B>Concrete, 28 days old (at 70% hydratation):</B></TD></TR>
<TR><TD>&nbsp;</TD><TD>bound water</TD><TD ALIGN="CENTER">85</TD></TR>
<TR><TD>&nbsp;</TD><TD>dried water</TD><TD ALIGN="CENTER">25 ... 45</TD></TR>
<TR><TD>&nbsp;</TD><TD>free water</TD><TD ALIGN="CENTER">65 ... 45</TD></TR>
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD ALIGN="CENTER">(sum = 175)</TD></TR>
<TR><TD COLSPAN="3"><B>Concrete, 3 to 6 months old (at 90% hydratation):</B></TD></TR>
<TR><TD>&nbsp;</TD><TD>bound water</TD><TD ALIGN="CENTER">105</TD></TR>
<TR><TD>&nbsp;</TD><TD>dried water</TD><TD ALIGN="CENTER">35 ... 50</TD></TR>
<TR><TD>&nbsp;</TD><TD>free water</TD><TD ALIGN="CENTER">35 ... 20</TD></TR>
<TR><TD>&nbsp;</TD><TD>&nbsp;</TD><TD ALIGN="CENTER">(sum = 175)</TD></TR>
<TR><TD COLSPAN="3">DIN 4108 "thermal protection"</TD></TR>
<TR><TD>&nbsp;</TD><TD><B>practical moisture content of concrete</B></TD><TD ALIGN="CENTER">50</TD></TR>
<TR><TD COLSPAN="3">&nbsp;</TD></TR>
<TR><TD COLSPAN="2"><B>Cellular concrete</B></TD><TD ALIGN="CENTER">180 ... 220</TD></TR>
<TR><TD COLSPAN="2"><B>Clay brick masonry</B></TD><TD ALIGN="CENTER">100 ... 150</TD></TR>
<TR><TD COLSPAN="2"><B>Calcium silica brick masonry</B></TD><TD ALIGN="CENTER">100 ... 120</TD></TR>
<TABLE>
 
<P>
&nbsp;
</P>
 
<P>
<B><A NAME="13">(13):</A></B><BR>
<B>How can I simulate a wall whose exterior surface has been treated with a
water-repellent agent? Is it correct to set the rain water absorption factor to zero?
Do I need to change the s<small>d</small>-value of the exterior surface, even though
I use a diffusion-permeable treatment?</B>
</P>
<P>
The
<A HREF="RainWaterAbsorptionFactor.htm">rain water absorption factor</A> must be
set to zero if the water absorption is indeed
completely stopped by the treatment. If water absorption is only reduced, you must
determine the
<A HREF="LiquidTransportCoefficients.htm">water absorption coefficient</A> for
the treated material and replace the part of the wall which corresponds to the
penetration depth of the treatment with da layer of the treated material.
</P>
<P>
If the treatment does not change the
<A HREF="WaterVaporDiffusion.htm">diffusion permeability</A> of the material, no
<A HREF="DialogEditSurfaceCoefficients.htm">s<small>d</small>-value</A> needs to
be specified for the exterior surface.<BR>
Many treatments do, however, increase the diffusion resistance factor (&micro;-value)
of the material. In these cases, this additional resistance should be allowed
for by an appropriate s<small>d</small>-value. Alternatively, and even better, you
can replace the part of the wall which corresponds to the penetration depth of the
treatment with a new layer that has the same material properties but an
appropriately increased &micro;-value.
</P>
<P>
Even if the water absorption is negligible (so that adjusting the rain absorption
factor instead of the liquid transport coefficients would be sufficient) and vapor
diffusion is not hindered by the treatment (so that no &micro;-value needs to be
adjusted), it might nevertheless be preferable to model the treated part of the
wall by defining a separate layer whose liquid transport coefficients have
been reduced or even set to zero.</BR>
This is because the capillary conduction in this layer does not only determine
the amount of absorbed rain water; it also influences the wall's drying behavior.<BR>
Drying-out proceeds faster if water from the interior of the wall can be conducted
to the surface by capillary transport and can evaporate from there. Drying-out
is impeded, however, if capillary transport stops a few centimeters behind the
surface and moisture can only dry out after crossing this treated layer by vapor
diffusion. So this is another mechanism by which water-repellent treatment may
reduce the drying potential of a wall, in addition to a possibly increased
&micro;-value.
</P>
 
<P>
<B><A NAME="14">(14):</A></B><BR>
<B>WUFI gives me the option to estimate the liquid transport coefficients
D<small>ws</small> from the water absorption coefficient. How can I check how
good this estimate is?</B>
</P>
<P>
You can check the <A HREF="LiquidTransportCoefficients.htm">estimated</A> Dws or
determine an unknown water absorption
coefficient from known Dws by simulating a water absorption experiment.
</P>
<P>
Define an initially dry layer consisting of the material in question, let it
rain on the surface (with a higher rain load than the layer can absorb to be
sure that no insufficient rain load is limiting the water uptake) and look
at the amount of water absorbed after e.g. 100 or 200 hours.
</P>
<P>
This may be done with a one-line *.KLI-file such as:
<TABLE>
<TR><TD WIDTH="14%">[h:</TD><TD WIDTH="14%">rain:</TD><TD WIDTH="14%">rad:</TD><TD WIDTH="14%">t_ext:</TD><TD WIDTH="14%">RH_ext:&nbsp;&nbsp;</TD><TD WIDTH="14%">t_int:</TD><TD>RH_int:]</TD></TR>
<TR><TD WIDTH="14%">500</TD><TD WIDTH="14%">1000</TD><TD WIDTH="14%">0</TD><TD WIDTH="14%">20</TD><TD WIDTH="14%">1</TD><TD WIDTH="14%">20</TD><TD>0</TD></TR>
</TABLE>
</P>
<P>
The number of hours entered for the duration of this one-line climate file does not
matter since WUFI re-starts reading from the beginning of the climate file if the
simulation period extends beyond the end of the climate file.
</P>
<P>
Set the vapor diffusion thickness of the interior surface to a very high value
to prevent vapor transport through that surface.
</P>
<P>
You should perform a few test calculations in order to find a suitable thickness
of the test specimen which assures that the moisture front traverses most of the
specimen (in order to make the most efficient use of the numerical grid) but not
all of it.
<P>
<P>
<IMG SRC="pix/e_BaumbergerSaug.gif" WIDTH="300" HEIGHT="225" VSPACE="0" HSPACE="0" ALT="">
</P>
 
<P>
<B><A NAME="15">(15):</A></B><BR>
<B>I want to evaluate the effect of different material parameters on water absorption by
simulating a laboratory experiment in which different specimens are exposed to a limited
water supply. I created the corresponding KLI file with a spreadsheet program to avoid
typing in all those numbers by hand, but WUFI can't read this KLI file.</B>
</P>
<P>
The reason why WUFI does not accept your spreadsheet file is probably that you did
not write it in ASCII format and/or did not write the header lines in the correct
format. Please consult the on-line help for details on creating *.KLI files with your
own programs.
</P>
<P>
Also note that if you want to simulate a simple absorption experiment with a specified constant
water supply and constant climate conditions it is sufficient to create a *.KLI file
which consists of only one single line, for example the line:
<TABLE>
<TR><TD WIDTH="14%">[h:</TD><TD WIDTH="14%">rain:</TD><TD WIDTH="14%">rad:</TD><TD WIDTH="14%">t_ext:</TD><TD WIDTH="14%">RH_ext:&nbsp;&nbsp;</TD><TD WIDTH="14%">t_int:</TD><TD>RH_int:]</TD></TR>
<TR><TD WIDTH="14%">1000</TD><TD WIDTH="14%">5</TD><TD WIDTH="14%">0</TD><TD WIDTH="14%">20</TD><TD WIDTH="14%">1</TD><TD WIDTH="14%">20</TD><TD>0.8</TD></TR>
</TABLE>
means that for 1000 hours after the starting time of the climate file there is a constant
rain load of 5 Ltr/m&sup2;h.
</P>
<P>
An alternative would be a single line like
<TABLE>
<TR><TD WIDTH="14%">[h:</TD><TD WIDTH="14%">rain:</TD><TD WIDTH="14%">rad:</TD><TD WIDTH="14%">t_ext:</TD><TD WIDTH="14%">RH_ext:&nbsp;&nbsp;</TD><TD WIDTH="14%">t_int:</TD><TD>RH_int:]</TD></TR>
<TR><TD WIDTH="14%">1 5</TD><TD WIDTH="14%">0</TD><TD WIDTH="14%">20</TD><TD WIDTH="14%">1</TD><TD WIDTH="14%">20</TD><TD>0.8</TD></TR>
</TABLE>
which states that for 1 hour after the starting time of the climate file there is
a constant rain load of 5 Ltr/m&sup2;h. When WUFI reaches the end of a climate file,
it starts reading the file anew from the beginning, so you can simulate an experiment
which is running for 100 hours (or whatever) and the climate file will automatically
be read 100 times over.
</P>
<P>
The only difference between these two files is that in the latter case WUFI does not
accept a calculation time step greater than 1 hour, whereas in the former case you
may also choose any convenient time step greater than one hour.
</P>
<P>
For a simple absorption experiment I usually make sure the climate file contains a
rain load large enough so that it does not limit the absorption of the specimen, for
example 100 Ltr/m&sup2;h, which ould not be plausible for real rain.
</P>
<P>
If you want to have a specified limited supply please don't forget that WUFI reduces
the amount of rain it reads from the climate file by the
<A HREF="RainWaterAbsorptionFactor.htm">rain absorption factor</A> which
allows for the fact that some rain splashes off of the wall on impact and is not
available for absorption. This factor should be set to 1 during your experiments.
</P>
<P>
Furthermore, please note a small subtlety involved in using limited rain supply.
Let's assume you have a specimen with a water absorption factor of
3 kg/m&sup2;h<sup>1/2</sup> and the climate file specifies a rain load of
3 Ltr/m&sup2;h. During each time step,
WUFI performs a <I>test</I> step with an <I>unlimited</I> supply and subsequently
evaluates the amount of water taken up. If this amount of water is less than the
amount supplied in the climate file, then the material is the limiting factor and
WUFI accepts the result of this time step and proceeds with the calculation.<BR>
However, if the amount taken up is more than the amount supplied, WUFI performs
additional iteration steps in which a fictitious 'flow resistance' at the specimen
surface is adjusted until the amount taken up matches the amount supplied.
</P>
<P>
If you are using 1-hour steps in your calculation, and the dry specimen
absorbs 3 kg/m&sup2; of water in the first step and the climate file supplies
3 kg/m&sup2;h, then WUFI accepts the trial step done with unhindered absorption
and proceeds with the calculation.<BR>
But if you are repeating the same calculation with a time step of half an hour,
things are different! Since the water uptake is not linear in time, the specimen
will absorb <I>more</I> than 1.5 kg/m&sup; in the first half hour, while WUFI compares
this with 1.5 kg/m&sup; of rain in the first half hour (assuming the rain is
evenly distributed over the hour) and now <I>limits</I> the amount absorbed to
1.5 kg/m&sup2;.<BR>
This is usually of no concern with real rain data and real building materials,
but it may be beneficial to be aware of these subtleties if performing test
calculations with limited rain supply.
</P>
 
<P>
<B><A NAME="16">(16):</A></B><BR>
<B>I'm familiar with steady-state water vapor diffusion calculations (in particular,
the Glaser method described in German standard DIN 4108). So I knew I had to expect
more or less frequent dew conditions in the wall I was simulating. However, when I
watched the WUFI film, I could never see the relative humidity reach 100%.</B>
</P>
<P>
The usual building materials always have some moisture sorption capacity. This
sorption capacity buffers changes in relative humidity inside the wall. If you
define boundary conditions which would provoke instant condensation in a Glaser
calculation, you may nevertheless not get condensation in a realistic case (such
as simulated by WUFI).
</P>
<P>
That's because a relative humidity of 100% would correspond to a
<A HREF="MoistureStorageFunction.htm">moisture content</A>
equal to free saturation of the material in question, and this amount of water must
first be transported into the dew region. The diffusion flows do transport moisture
to the location where dew conditions prevail, but the transported amounts of moisture
are generally small, and the RH will only slowly rise from the initial value,
say 80%, to 81%, 82% etc. It may take days or weeks until sufficient amounts of
water have been transported to the dew region so that finally free saturation
(i.e. RH=100%) is reached. Meanwhile, boundary conditions may have changed and
there are no dew conditions any more.
</P>
<P>
The Glaser method, on the other hand, simply assumes that 100% RH are reached
instantly, it doesn't consider the necessity to actually move water in order to
reach the moisture content that corresponds to 100% RH.
</P>
<P>
Furthermore, real materials (as opposed to Glaser) usually have some
<A HREF="LiquidTransportCoefficients.htm">capillary conductivity</A> which
tries to dispel any moisture accumulations. This effect
actively works against local water build-up, so that 100% RH can't be reached
easily.
</P>
<P>
Of course, you <I>may</I> get water accumulation in your building component if
conditions are right (or wrong). But this will rarely be accompanied by 100% RH.
If you see relative humidity approaching 100% somewhere in your component, it's
probably much too late...
</P>
 
<P>
<B><A NAME="17">(17):</A></B><BR>
<B>OK, this explains why I didn't see dew conditions in the wall. But shouldn't
condensation at least happen at the facade on days with high humidity and little
sunshine?</B>
</P>
<P>
The surface of a normal wall in temperate or cool climate regions will always
be somewhat warmer than the surrounding air. By day because of solar radiation
(even on foggy or overcast days), by night because of heat flow from indoors
(exceptions: air-conditioned dwellings or nightly emission, see below).<BR>
Since the RH in the air can't be greater than 100% and the RH at the warmer-than-air
wall surface will always be less than the RH of the air, you usually can't reach or
surpass 100% there.
</P>
<P>
You'll have
<A HREF="MoistureStorageFunction.htm">free saturation</A> (i.e. 100% RH) at the
surface when enough rain is absorbed, but this is not due to dew conditions.
</P>
<P>
The surface temperature will fall below air temperature when the wall
<A HREF="LongWaveRadiationEmissivity.htm">emits</A> more
long-wave radiation than it gets back from surrounding surfaces. If it even falls
below the dew-point temperature, you will indeed get dew conditions at the surface.<BR>
This happens routinely during the night, especially during clear nights, when the
long-wave emission of the water vapor in the atmosphere is at a minimum.
</P>
<P>
In these cases you may get repeated and regular wetting of the surface which may
lead to dust accumulation or algae growth, especially with exterior insulations
whose surfaces cool down particularly strongly.<BR>
Currently, WUFI does not routinely allow for this effect, since the necessary
data on atmospheric and terrestrial counterradiation are rarely available. If
these data are provided, WUFI can compute nightly emission cooling in principle,
but only approximately. Future WUFI versions will have a more sophisticated
emission model incorporated.
</P>
 
<P>
<B><A NAME="18">(18):</A></B><BR>
<B>I used WUFI to compute the water content in a variety of wall assemblies. In
order to evaluate their hygrothermal performance, I now need appropriate criteria,
e.g. standards that should not be exceeded.</B>
</P>
 
<P>
There are no general criteria which are applicable for every case. Different
materials and different applications require different criteria. Here are some
general hints:
</P>
 
<UL>
<LI>The most important criterion: the moisture must not accumulate over time. Water
condensing in the building component must be able to dry out again. If the
moisture content in your component keeps increasing - even slowly - you'll run
into problems sooner or later.</LI>
 
<LI>The building materials which come into contact with moisture must not be damaged
(e.g. by corrosion or mould growth).<BR>
Mineral building materials are usually not at risk; some of them may be susceptible
to frost damage if they contain a lot of moisture.<BR>
Wood should not exceed 20 mass-% of moisture during a prolonged period; otherwise
mould growth may result (possible exception: increased moisture while temperatures
are low).<LI>
</UL>
<P>
German standard DIN 4108-3 adds the following criteria:
</P>
<UL>
<LI>The amount of condensing moisture in roof or wall assemblies must not exceed
a total of 1.0 kg/m&sup2;.<BR>
This is a more or less arbitrary criterion. In order to test it with WUFI, start
the calculation with the normal equilibrium moisture (corresponding to 80% RH) and
see if the total water content exceeds the starting value by more than 1 kg/m&sup2;.</LI>
 
<LI>At interfaces between materials that are not capillary-active, no moisture
increase exceeding 0.5 kg/m&sup2; is permissible.<BR>
This is meant to avoid moisture running or dripping off, which could accumulate
elsewhere and cause damage.</LI>
 
<LI>The moisture increase in wood must not exceed 5 mass-%, the moisture increase
in materials made of processed wood must not exceed 3 mass-%.<BR>
These are more or less arbitrary numbers.</LI>
</UL>
<P>
In addition, special criteria may be applicable in specific cases, for example:
</P>
<UL>
<LI>Are there any materials which are particularly sensitive to moisture damage?</LI>
<LI>Does increased heat loss by moist insulation exceed any energy conservation
requirements?</LI>
<LI>Is the building material at this moisture level sensitive to frost damage?</LI>
<LI>Is there salt in the wall which must be kept from crystallizing or from moving
around?</LI>
<LI>Etc.</LI>
</UL>
<P>
Even if you don't have clear criteria which fit your case, you may still perform a
<I>ranking</I> of your assemblies by comparing them with each other or with a
standard case.
</P>
 
<P>
<B><A NAME="19">(19):</A></B><BR>
<B>I want to simulate a ventilated curtain wall; how can I do this? I can model
the air gap as an air layer in WUFI but it seems these air layers are assumed
to be stagnant, which is certainly not the case in my ventilation gap.</B>
</P>
 
<P>
If you model the ventilation gap as an
<A HREF="AirLayers.htm">air layer</A> in WUFI, it is indeed treated as a
closed air layer without connection to the exterior air. The effect of inner
convection on heat and moisture transport across the air layer is allowed for
(as a first approximation) by use of
<A HREF="AirLayers.htm">effective</A>
<A HREF="MaterialData.htm">heat conductivities</A> and
<A HREF="MaterialData.htm">vapor diffusion resistance factors</A>.
</P>
<P>
The air flow and air exchange phenomena in a ventilated air layer cannot be
simulated with a one-dimensional program like WUFI-1D; WUFI-2D currently does not
take air flows into account.<BR>
If the air exchange is large enough, it may be justified to assume exterior air
conditions in the air gap. That is, you do not model the curtain facade and the
air gap, and you consider the surface of the insulation or the wall itself (as the
case may be) as the exterior surface in WUFI's component assembly. Rain must be
set to zero (simply by setting the
<A HREF="RainWaterAbsorptionFactor.htm">rain absorption factor</A> = 0).<BR>
It will be advisable to choose appropriate effective values for the exterior
heat transfer coefficient and the short-wave solar absorptivity, but this
requires calibration by experimental data.
</P>
<P>
The same problem is encountered in simulations of roofs, either because of a
ventilation cavity in the roof or because of the question how to model the
covering and the batten space.
</P>
<P>
The investigations described in [1] used a simplified treatment of a roof. WUFI-1D
simulations were carried out to examine the moisture balance in a fully insulated
west-facing pitched roof (50° inclination). The covering and the batten space
could be omitted from the simulated assembly because measured temperatures in a
similar roof on IBP's testing area were available and could be used to determine
appropriate effective surface transfer coefficients. The measurements were taken
on the waterproofing foil (i.e. directly on the insulation layer) and were
compared with the computed temperatures at the outer surface of the modeled
insulation layer which sufficed to represent the whole roof for the purpose
of a thermal adjustment.<BR>
The thermal surface transfer coefficients were adjusted in WUFI until good
agreement between measurement and calculation was reached. This was the case
with an effective short-wave absorptivity of a<small>s</small>=0.6 and an
effective heat transfer coefficient of <FONT FACE="SYMBOL">a</FONT>=19 W/m&sup2;K.
The effective absorptivity is roughly identical with the real absorptivity
(for red roof tiles), while the effective <FONT FACE="SYMBOL">a</FONT> is slightly
higher than the usual standard value of 17 W/m&sup2;K. Obviously the covering
and the air in the batten space have no major effect on the thermal behavior of
the roof, at least in this case. In particular, the amount of heat removed by
convection through the ventilated air cavity seems negligible and the entire
heat created in the covering by solar radiation is passed on into the underlay.<BR>
The question to which extent this isolated result can be generalised could only
be answered by more extensive comparisons with measurements.
</P>
<P>
[1] H.M. K&uuml;nzel: Au&szlig;en dampfdicht, vollged&auml;mmt? - Die rechnerische
Simulation gibt Hinweise zu dem Feuchteverhalten au&szlig;en dampfdichter
Steild&auml;cher. bauen mit holz 8/98, S. 36-41.
</P>
 
<P>
<B><A NAME="20">(20):</A></B><BR>
<B>I calculated the sum of the heat flows through the exterior and the interior
surfaces during one year and I noted that the heat flow out of the building
component through the exterior surface is much larger than the heat flow into
the component through the interior surface. But shouldn't they be nearly equal?
How can more heat flow out of the component than into it? No heat can be created
in the wall.</B>
</P>
 
<P>
The solar radiation incident on the exterior surface is electromagnetic radiation
and not heat flow; it is therefore not included in the heat flow data.<BR>
However, after absorption it is converted to heat so that there exists indeed a
heat source in the wall. Since the heat source is close to the exterior surface,
most of the generated heat flows outward through the exterior surface, only a
small amount flows inward through the interior surface. This asymmetric heat flow is
superimposed on the usual transmission heat flow (which in colder climates alway
goes from the indoor side to the outdoor side of the building element).
</P>
<P>
Please note that in the film display the heat flow arrow at the exterior surface
does include the solar radiation. Otherwise it would look very strange to see the
sun shining on the wall surface but a lot of heat flowing out of the wall. This is a
concession to the intuitive expectations of the audience.
</P>
<P>
Also note that there can be a heat source or sink in the wall when water condenses
or evaporates. In some cases these latent heat effects can be non-negligible (e.g.
drying of a wall wetted by driving rain).
</P>
 
<P>
<B><A NAME="21">(21):</A></B><BR>
<B>Are there more recent weather data available? The copy of WUFI I downloaded still
has those of 1991.</B>
</P>
 
<P>
'Recent' weather data would probably not be very useful to you. It is more important
to have weather data which are either known to be typical for a specific location
or which repesent defined critical conditions (e.g. for design purposes). We
consider 1991 to be a fairly typical year for Holzkirchen. 'Critical' weather data,
i.e. one particularly cold year and one particularly warm year, are in preparation
and may be made available as two 'Hygrothermal Reference Years'.
</P>
 
<P>
<B><A NAME="22">(22):</A></B>
<B>For the numerical solution of the transport equations the component must be divided
into a series of grid elements for whose midpoints the resulting temperatures and water
contents are computed at each time step, and across whose element boundaries the heat
and moisture fluxes required by the equations are flowing. In order to arrive at correct
fluxes across the boundaries, effective conductivities have to be assigned to the
boundaries which represent the integral effect of the conductivities between the
midpoints of the two elements. The investigations reported in [1] show that the results
do in fact depend on the way these effective heat and moisture conductivities are
determined from the real conductivities of the two elements: obviously linear
interpolation between the neighboring conductivities is preferable within a material
layer, and a resistance formulation is more appropriate for boundaries between layers
with different materials. How does WUFI treat these element boundary
conductivities?</B><BR>
</P>
 
<P>
It is obvious that at element boundaries where materials with possibly very different
conductivities are in contact with each other a simple average of the conductivities
(or resistances) cannot result in a realistic effective conductivity to describe the
fluxes between the elements. Take as an example a material with very low resistance
which borders on a material with very high resistance. The flux flowing between the
midpoints of the two elements is determined by the sum of the two successively
encountered resistances, not by the arithmetical average of the conductivities.<BR>
One might suppose now that this physically motivated reasoning also applies to
smaller differences between the neighboring elements and that therefore the resistance
formulation (i.e. the harmonic mean of the conductivities) should always be used
within the entire component. However, test calculations during the development
of WUFI's numerics showed that this is not the case. Within a material the
arithmetical mean of the conductivities yielded better results (compared with
experimental data), so that WUFI uses harmonic averages at material boundaries and
arithmetical averages within a material, in agreement with the cited investigation.
The derivation of the resistance formulation assumes equal fluxes in the two element
halves, but this need not be the case if transient processes in materials with heat
or moisture storage capacities are considered.
</P>
<P>
[1] Galbraith, G.H. et al.: Evaluation of Discretized Transport Properties for
Numerical Modelling of Heat and Moisture Transfer in Building Structures,<BR>
Journal of Thermal Env. & Bldg. Sci., Vol. 24, Jan. 2001
</P>
 
<P>
<B><A NAME="23">(23):</A></B><BR>
<B>I want to perform a hygrothermal simulation of a wall on which every day a shadow
is cast for some time by a building on the other side of the street. WUFI does not
offer an option to allow for such a shadow, but I could simply use a self-created *.KLI
file by converting the measured radiation myself and allowing for the sadow in this
process. But, how is the conversion of the radiation data done?</B>
</P>
 
<P>
First you need to determine the radiation incident on the surface of your building element
from the measured data describing the radiation on a horizontal surface. For this purpose
it is necessary to determine the position of the sun in the sky at the time of the
measurement.
</P>
 
<H3>Position of the Sun:</H3>
 
<P>Let <TT>J</TT> be the number of the day in the year (1 .. 365 or 366). Then
compute the auxiliary quantity <TT>x</TT>:
</P>
<P>
<TT>x = 0.9856&deg; * J - 2.72&deg;</TT>
</P>
<P>
and the equation of time <TT>Z</TT> (in minutes):
</P>
<P>
<TT>Z = -7.66*sin(x) - 9.87*sin( 2*x + 24.99&deg; + 3.83&deg;*sin(x) ).</TT>
</P>
<P>
The equation of time describes the variable difference in time between the actual
culmination of the sun and noon. Because of the ellipticity of the Earth's orbit
and the obliquity of the Earth's axis the sun wanders with slightly irregular
speed across the sky. During the course of the year there are thus times where it
reaches culmination earlier than a fictitious sun with constant speed (the so-called
'mean' sun) and times where it reaches culmination later.
</P>
<P>
The local meridian is the great circle that rises from the horizon due north,
passes through the point directly above the observer and crosses the horizon again
due south. The instant at which the sun crosses the local meridian on its daily path
from east to west is also the instant where its position is due south and where it
reaches its daily greatest height.
</P>
<P>
When the apparent sun (i.e. the actually observed sun) crosses the meridian it
is 12 noon local apparent solar time (<TT>LAT</TT>); when the mean sun crosses the
meridian it is 12 noon local mean time (<TT>LMT</TT>). The equation of time is
therefore the difference between <TT>LAT</TT> and <TT>LMT</TT> (<TT>Z = LAT - LMT</TT>).
</P>
<P>
Furthermore, since the place where the measurements were taken is usually not
located on the reference meridian of the time zone (15° East for the Central
European Time Zone, <TT>CET</TT>), the difference between local mean time and
zone time must be allowed for, which is 4 minutes for 1&deg; difference in
geographical longitude <TT>L</TT> and one hour for 15&deg; difference. If the
measurement was timed in Central European Summer Time <TT>CEST</TT>, convert
to <TT>CET</TT> first by subtracting one hour (<TT>CET = CEST - 1h</TT>).
</P>
<P>
In this way you can now compute the corresponding local apparent time
<TT>LAT</TT> from the known measurement time (in <TT>CET</TT>):
</P>
<P>
<TT>LAT = CET - (15&deg;-L)/(15&deg;/h) + Z/(60 min/h) [h]</TT>
</P>
<P>
and thus determine the position of the sun: at 12 noon <TT>LAT</TT> the sun is
exactly on the meridian, before noon it stands at an appropriate distance to
the east of the meridian, after noon, an appropriate distance to the west.<BR>
The distance between the sun and the meridian is measured by the hour angle:
</P>
<P>
<TT><FONT FACE="SYMBOL">w</FONT> = (LAT - 12h) * 15&deg;/h.</TT>
</P>
<P>
The hour angle <FONT FACE="SYMBOL">w</FONT> is reckoned perpendicular to the meridian;
it is negative before noon, zero at noon and positive after noon; it increases
steadily by 15&deg; per hour.
</P>
<P>
The hour angle gives the distance of the sun from the meridian; the declination
<FONT FACE="SYMBOL">d</FONT>, i.e. the distance of the sun from the celestial equator,
then fixes the position of the sun completely. The declination varies between
-23&deg;26' at winter solstice, 0&deg; at the equinoxes, and 23&deg;26' at the summer
solstice. Since its change during one day is very small, it suffices to compute it
once for the day <TT>J</TT> under consideration:
</P>
<P>
<TT>
sin(<FONT FACE="SYMBOL">d</FONT>) = 0.3978 * sin( x - 77.51&deg; + 1.92&deg; * sin(x) ),<BR>
cos(<FONT FACE="SYMBOL">d</FONT>) = sqrt(1 - sin(<FONT FACE="SYMBOL">d</FONT>)^2)
</TT>
</P>
<P>
where <TT>x</TT> is the auxiliary quantity introduced above.
</P>
<P>
The last step is the transformation from the coordinate system determined
by <FONT FACE="SYMBOL">w</FONT> and <FONT FACE="SYMBOL">d</FONT> into the more
familiar coordinates altitude <FONT FACE="SYMBOL">g</FONT> and azimuth
<FONT FACE="SYMBOL">y</FONT> (=compass direction). The geographical latitude
<FONT FACE="SYMBOL">j</FONT> of the measurement location is needed for this.
</P>
<P>
<TT>
sin(<FONT FACE="SYMBOL">g</FONT>) = cos(<FONT FACE="SYMBOL">d</FONT>)*cos(<FONT FACE="SYMBOL">w</FONT>)*cos(<FONT FACE="SYMBOL">j</FONT>)+sin(<FONT FACE="SYMBOL">d</FONT>)*sin(<FONT FACE="SYMBOL">j</FONT>)<BR>
cos(<FONT FACE="SYMBOL">g</FONT>) = sqrt(1 - sin(<FONT FACE="SYMBOL">g</FONT>)^2)<BR>
&nbsp;<BR>
if cos(<FONT FACE="SYMBOL">g</FONT>)=0 then <FONT FACE="SYMBOL">y</FONT> = 0<BR>
else begin<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sin(<FONT FACE="SYMBOL">y</FONT>) = cos(<FONT FACE="SYMBOL">d</FONT>)*sin(<FONT FACE="SYMBOL">w</FONT>)/cos(<FONT FACE="SYMBOL">g</FONT>)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;cos(<FONT FACE="SYMBOL">y</FONT>) = (cos(<FONT FACE="SYMBOL">d</FONT>)*cos(<FONT FACE="SYMBOL">w</FONT>)*sin(<FONT FACE="SYMBOL">j</FONT>)-sin(<FONT FACE="SYMBOL">d</FONT>)*cos(<FONT FACE="SYMBOL">j</FONT>))/cos(<FONT FACE="SYMBOL">g</FONT>)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT FACE="SYMBOL">y</FONT> = atn2(sin(<FONT FACE="SYMBOL">y</FONT>), cos(<FONT FACE="SYMBOL">y</FONT>))<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;end
</TT>
</P>
<P>
This formula uses <TT>atn2(A,B)</TT>, the arctangent function for two arguments
<TT>A</TT> and <TT>B</TT>, which is provided by many programming languages, and which
gives the arctangent of <TT>A/B</TT> in the correct quadrant. If this function is
not available to you, you can use the ordinary arctangent and then explicitly determine
the correct quadrant (i.e. you compute <TT>y=atn(A/B)</TT>, and in the case <TT>B<0</TT>
you add <TT>180&deg;</TT> if <TT>y<=0</TT> or subtract <TT>180&deg;</TT> if <TT>y>0</TT>.
If <TT>B=0</TT> and <TT>A<0</TT> then <TT>y=-90&deg;</TT>, if <TT>B=0</TT> and
<TT>A>0</TT>, then <TT>y=+90&deg;</TT>.).<BR>
The azimuth <FONT FACE="SYMBOL">y</FONT> is counted from south=0&deg;, positive
towards the west and negative towards the east.
</P>
<P>
Examples for Munich (<TT>48.13&deg;N</TT>, <TT>11.58&deg;E</TT>):
</P>
<TABLE>
 
<TR ALIGN="CENTER"><TD>CET</TD><TD>Altitude</TD><TD>Azimuth</TD><TD>Declination</TD></TR>
<TR><TD COLSPAN="4"><TT>(J=1)</TT></TD></TR>
<TR ALIGN="RIGHT"><TD><TT> 1 Jan. 2001 09:00</TD><TD> 6.436&deg;</TD><TD>-44.614&deg;</TD><TD>-22.987&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT> 1 Jan. 2001 12:00</TD><TD>18.836&deg;</TD><TD> -4.209&deg;</TD><TD>-22.977&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT> 1 Jan. 2001 16:00</TD><TD> 3.441&deg;</TD><TD> 49.590&deg;</TD><TD>-22.962&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT> 1 Jan. 2001 16:25</TD><TD> 0.434&deg;</TD><TD> 54.316&deg;</TD><TD>-22.961&deg;</TD></TR>
<TR><TD COLSPAN="4">&nbsp;</TD></TR>
<TR><TD COLSPAN="4"><TT>(J=79)</TT></TD></TR>
<TR ALIGN="RIGHT"><TD><TT>20 Mar. 2001 07:00</TD><TD> 6.498&deg;</TD><TD>-82.661&deg;</TD><TD> -0.126&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT>20 Mar. 2001 12:21</TD><TD>41.851&deg;</TD><TD> -0.041&deg;</TD><TD> -0.038&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT>20 Mar. 2001 16:00</TD><TD>22.726&deg;</TD><TD> 62.242&deg;</TD><TD> +0.022&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD COLSPAN="4">&nbsp;</TD></TR>
<TR><TD COLSPAN="4"><TT>(J=172)</TT></TD></TR>
<TR ALIGN="RIGHT"><TD><TT>21 Jun. 2001 08:00</TD><TD>34.501&deg;</TD><TD>-87.522&deg;</TD><TD>+23.437&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT>21 Jun. 2001 12:00</TD><TD>65.126&deg;</TD><TD> -8.437&deg;</TD><TD>+23.437&deg;</TD></TR>
<TR ALIGN="RIGHT"><TD><TT>21 Jun. 2001 18:00</TD><TD>19.771&deg;</TD><TD>103.475&deg;</TD><TD>+23.436&deg;</TD></TR>
</TABLE>
 
<P>
These values were computed with an astronomical ephemeris program. Of course, the
simplified method described above cannot reproduce these data exactly, in particular
for low altitudes of the sun (<TT>1 Jan. 16:25</TT>), since it does not allow for
atmospheric refraction. On the other hand, the comparison allows you to assess the
overall accuracy of this simple method. Your results should agree with these exact
positions within a few tenths of a degree. The declinations have been included
as well for testing purposes.
</P>
 
<P>
&nbsp;
</P>
 
<H3>Converting the Radiation Data:</H3>
<P>
We assume that your input data are measured hourly values of the global
(<TT>I_glob</TT>) and the diffuse radiation (<TT>I_diff</TT>) on a horizontal surface.
</P>
<P>
The radiation incident on the measuring or the component surface is split up into
a direct and a diffuse component. The direct component is received directly from
the sun and is therefore a directed quantity that depends on the position of the
sun. The direct radiation vertically incident on a surface which is facing the
sun is the direct normal radiation <TT>I_dir_normal</TT>. The direct radiation
<TT>I_dir</TT> obliquely incident on a horizontal measuring surface depends on
the solar altitude <FONT FACE="SYMBOL">g</FONT>:
</P>
<P>
<TT>I_dir = I_dir_normal * sin(<FONT FACE="SYMBOL">g</FONT>)</TT>.
</P>
<P>
Since <TT>I_dir</TT> can be computed as the difference between the measured values
of global and diffuse radiation and <FONT FACE="SYMBOL">g</FONT></TT> can be determined
from the measurement location and time by the method given above, the corresponding
direct normal radiation is
</P>
<P>
<TT>I_dir_normal = (I_glob - I_diff) / sin(<FONT FACE="SYMBOL">g</FONT>).</TT>
</P>
<P>
The angle of incidence <FONT FACE="SYMBOL">h</FONT>, i.e. the angle that the direct
normal radiation makes with the normal to the component surface which is tilted by
the angle <FONT FACE="SYMBOL">b</FONT> and oriented in the
direction <FONT FACE="SYMBOL">a</FONT>, is
</P>
<TABLE>
<TR><TD COLSPAN="2">cos(<FONT FACE="SYMBOL">h</FONT>) = sin(<FONT FACE="SYMBOL">g</FONT>)*cos(<FONT FACE="SYMBOL">b</FONT>) + cos(<FONT FACE="SYMBOL">g</FONT>)*sin(<FONT FACE="SYMBOL">b</FONT>)*cos(<FONT FACE="SYMBOL">a</FONT>-<FONT FACE="SYMBOL">y</FONT>)</TD></TR>
<TR><TD><FONT FACE="SYMBOL">h</FONT>:</TD><TD>Angle of incidence (vertical=0&deg;)</TD></TR>
<TR><TD><FONT FACE="SYMBOL">g</FONT>:</TD><TD>Altitude of the sun</TD></TR>
<TR><TD><FONT FACE="SYMBOL">y</FONT>:</TD><TD>Azimuth of the sun (south=0&deg;, positive towards west, negative towards east)</TD></TR>
<TR><TD><FONT FACE="SYMBOL">b</FONT>:</TD><TD>Tilt of the component surface (vertical wall=90&deg;)</TD></TR>
<TR><TD><FONT FACE="SYMBOL">a</FONT>:</TD><TD>Azimuth of the normal to the component surface (south=0&deg;, west positive).</TD></TR>
</TABLE>
<P>
The direct radiation incident on the component surface is therefore:
</P>
<P>
<TT>
I_dir_in = I_dir_normal * cos(<FONT FACE="SYMBOL">h</FONT>)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= (I_glob - I_diffus) * cos(<FONT FACE="SYMBOL">h</FONT>) / sin(<FONT FACE="SYMBOL">g</FONT>).
</TT>
</P>
<P>
The diffuse component consists of the radiation scattered by the air ("blue sky")
and the clouds which comes from all directions and can approximately be treated
as isotropic. Diffuse radiation is measured by blocking the direct radiation
with a shadow ring around the solarimeter. The measurement gives <TT>I_diff</TT>,
the diffuse radiation incident on the horizontal measuring surface from the entire
sky hemisphere. A component surface with arbitrary tilt and orientation receives
the same diffuse radiation (since it is isotropic), but for non-horizontal
surfaces the fact has to be allowed for that the sky covers a smaller part of
its field of view and the total amount of incident diffuse radiation is reduced proportionately (a vertical wall sees sky only in the upper half of its field of view):
</P>
<P>
<TT>I_diff_in = I_diff * ( cos(<FONT FACE="SYMBOL">b</FONT>/2) )^2</TT>.
</P>
<P>
Additionally, you may add the global radiation reflected from the ground:
</P>
<P>
<TT>I_refl_in = <FONT FACE="SYMBOL">r</FONT> * I_glob * ( sin(<FONT FACE="SYMBOL">b</FONT>/2) )^2</TT>,
</P>
<P>
where <FONT FACE="SYMBOL">r</FONT> is the short-wave albedo of the ground and the
reflection is assumed to be isotropic. In the current version, WUFI ignores the
reflected component of the radiation.
</P>
<P>
The total radiation incident on the surface of the building component is the sum
of the components:
</P>
<P>
<TT>I_in = I_dir_in + I_diff_in + I_refl_in</TT>.
</P>
<P>
You may now modify or supplement this conversion method according to your needs.
For example, you can allow for shadows by setting the direct radiation to zero at
times where the sun is behind the obstacle, and by reducing at all times the
diffuse radiation in proportion to the reduction of the field of view caused
by the obstacle. On the other hand, at times where the sun illuminates the facing
side of the obstacle, it may be necessary to add some reflected radiation.
</P>
<P>
Hint: if the radiation data to be converted have been averaged over some longer
interval (e.g. one hour), please note the following:
</P>
<P>
It is advisable to compute the solar positions for the middle of the measuring
interval, i.e. the averaged data measured between <TT>9h</TT> and <TT>10h</TT>
should be converted using the solar position computed for <TT>9:30h</TT>.<BR>
If the sun has risen or set during such a measuring intervall (which is easy to
check for, using the solar altitude), the solar position must be computed for
the middle of the visibility interval, not for the middle of the measuring interval.
</P>
<P>
Independent of the duration of the measuring interval, radiation data obtained
at very low solar altitudes should not be used, since under these circumstances
the direct normal radiation must be calculated from very small and unreliable
values obtained for the direct radiation at grazing angles of incidence.
</P>
<P>
Details on these conversion methods can be found in:<BR>
VDI 3789 Umweltmeteorologie, Blatt 2: Wechselwirkungen zwischen Atmosphäre und Oberflächen; Berechnung der kurz- und der langwelligen Strahlung.
</P>
<P>
In addition to data on global and diffuse radiation, the weather file
<TT>IBP1991.WET</TT> included with WUFI contains radiation data obtained with
a west-facing solarimeter which you can use to test your conversion routines.
</P>

Aktuelle Version vom 13. Juni 2013, 13:35 Uhr

Questions and Answers

This collection of Questions and Answers refers to the one-dimensional version of WUFI. Some of the program features mentioned here may not apply to WUFI-2D.

  1. Sources of Material Data
  2. Sources of Climate Data
  3. Volume Percent, Mass Percent
  4. Relative Humidity in a Building Component
  5. Default Moisture Storage Function
  6. Water Content of an Air Layer
  7. Convergence Failure Caused by Vapor-Permeable Layer
  8. Moisture Content at a Monitoring Position
  9. Liquid Transport Coefficient of a Paint Layer
  10. Rain Absorption Factor of an Unrendered Sandstone Wall
  11. Hygric Parameters of Ecological Insulation Materials
  12. Typical Initial Moisture Content
  13. Water-Repellent Facade
  14. Simulation of Absorption Experiment
  15. Absorption Experiment with Limited Water Supply
  16. Why Never 100% RH in the Component?
  17. 100% RH at the Facade
  18. Criteria for Evaluating Hygrothermal Performance
  19. Ventilated Curtain Walls
  20. Heat Flow Through Exterior Surface Is Not Realistic?
  21. More Recent Weather Data?
  22. Averaging of Conductivities at Element Boundaries
  23. Conversion of Radiation Data for Other Directions
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