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Details:BasicMaterialData

2009-07-03T08:10:42Z

GauertV:

= Basic Material Data =

These material data constitute an indispensable minimum without
which a calculation is not possible:

<DL>
<DT>• Bulk density [kg/m³],
<DD>
serves to convert the specific heat by mass to the specific heat
by volume. 
  
The bulk density ρbulk
is the ratio of the mass m of the sample and the total volume
Vtot of the sample:
<math>\rho_{bulk} = m / V_{tot}</math>. 
The true density ρtrue, by
contrast, is the ratio of the mass of the sample and the volume taken
up by the material matrix only:
ρtrue = m /
(Vtot - Vpores) = m / Vtrue. 
  
The bulk density should be available for virtually every building
material. If not, it can be measured very easily. Since it only affects
the specific heat value entering into the calculation, and hygrothermal
simulations usually don't depend very sensitively on this value, it need
not be known with great precision. 
 

<DT>• Porosity [m³/m³],
<DD>
determines the
[[Details:MoistureStorageFunction | maximum water content]]
wmax (by
multiplication by ρwater = 1000 kg/m³). 
  
Since most calculations are not sensitive to the exact value of the
maximum water content (you'll rarely encounter water contents above
[[Details:MoistureStorageFunction | free saturation]], it
is usually sufficient to estimate it if no value
is available for the material in question. 
  
The porosity can be estimated from the true density
ρtrue and the bulk
density ρbulk: 
ρbulk = m / Vtot = m / (Vtrue + Vpores) = ρtrue / (1 + Vpores/Vtrue) = ρtrue * Vtrue/Vtot = ρtrue * (1 - Vpores/Vtot) = ρtrue * (1 - porosity), therefore 
  
<CENTER>porosity = 1 - ρbulk / ρtrue.</CENTER>
  
ρtrue can in turn be
estimated from other materials which have the same composition but
different bulk density, if their bulk density and porosity are known.
Example: a cellular concrete brick with ρbulk = 600 kg/m³ and porosity = 0.72 has
ρtrue =
600 / (1 - 0.72) kg/m³ = 2140 kg/m³. The porosity of a
cellular concrete brick with ρbulk = 400 kg/m³ can then be estimated as
porosity = 1 - 400 / 2140 = 0.81. 
  

<DT>• Heat capacity [J/kgK],
<DD>
the specific heat capacity by mass of the dry material. 
  
Using the specific heat capacity by mass has the advantage that this
value only depends on the chemical composition of the material, but
not on its porosity. For example, cellular concrete bricks with
bulk densities of 400 kg/m³ and 600 kg/m³ have the same
specific heat capacity by mass. 
  
To convert into heat capacity by volume (which enters into the
transport equations), WUFI multiplies the mass-specific heat capacity
by the bulk density. 
  
Rough values are 850 J/kgK for mineral materials and 1500 J/kgK for
organic materials. In most cases, these estimates will be sufficient
since hygrothermal simulations usually don't depend very sensitively on
this value.
 

WUFI automatically allows for the additional heat capacity of the
water content, if any. 
  

<DT>• Heat conductivity dry [W/mK],
<DD>
the heat conductivity of the material in dry condition. A
[[Details:HeatConductivityMoistureDependent | moisture-dependent
heat conductivity]] is optional. 
  
Please note that experimentally measured heat conductivities
of vapor-permeable materials may include the effect of vapor
transport with phase change (i.e. water evaporating at one
side of the specimen and condensing at the other side, thus
in effect transporting latent heat without a corresponding
heat flow being conducted across the specimen). Since WUFI
explicitly computes this thermal effect of vapor flow, it
should not be included in the heat conductivity, if possible.
However, it is usually difficult or impossible to separate
this effect out of the measured data. 
  
Furthermore, design values, such as the data given in German
Standard DIN 4108, may already contain the contribution of a
typical water content and, if so, are not strictly dry values. 
If you want to perform the calculation with a constant (i.e. not
moisture-dependent) heat conductivity (for example because you
have no detailed data on the moisture-dependence), you may use
these design values to allow for moisture content at least in
a crude approximation. However, if you explicitly use a table of
[[Details:HeatConductivityMoistureDependent | moisture-dependent]]
heat conductivities, you should make sure
that the value for moisture content = 0 is really the dry value. 
  
On the other hand, hygrothermal simulations (in particular the
resulting moisture contents and distributions) usually don't depend
very sensitively on the precise values of the heat conductivities,
so the difference may be generally negligible unless you are
specifically interested in heat flows. 
  

<DT>• Diffusion resistance factor dry [-]
<DD>the diffusion resistance factor (µ-value) of the
material in dry condition. The µ-value states by how much
the diffusion resistance of the material in question is higher
than that of stagnant air. A
[[Details:DiffusionResistanceFactorMoistureDependent | moisture-dependent µ-value]]
is optional. 
  
The definition of the µ-value and its relation to
permeability are discussed in the topic
[[Details:WaterVaporDiffusion|Water Vapor Diffusion]]. 
  
Please note that even if you do not explicitly use a
[[Details:DiffusionResistanceFactorMoistureDependent|moisture-dependent]]
µ-value, WUFI will treat it as
moisture-dependent for moisture contents above free
saturation wf. WUFI will reduce it in proportion
to the moisture excess over wf, until it reaches
µ=0 at wmax. This reflects - in a first
approximation - the fact that at very high moisture contents
even the larger capillaries become clogged with water and can't
contribute to vapor transport any more.

Details:BasicMaterialData

2009-07-03T08:05:30Z

GauertV:

= Basic Material Data =

These material data constitute an indispensable minimum without
which a calculation is not possible:

<DL>
<DT>• Bulk density [kg/m³],
<DD>
serves to convert the specific heat by mass to the specific heat
by volume. 
  
The bulk density ρbulk
is the ratio of the mass m of the sample and the total volume
Vtot of the sample:
<math>\rho_{bulk} = m / V_{tot}</math>. 
<math>ρbulk = m / Vtot</math>. 
The true density ρtrue, by
contrast, is the ratio of the mass of the sample and the volume taken
up by the material matrix only:
ρtrue = m /
(Vtot - Vpores) = m / Vtrue. 
  
The bulk density should be available for virtually every building
material. If not, it can be measured very easily. Since it only affects
the specific heat value entering into the calculation, and hygrothermal
simulations usually don't depend very sensitively on this value, it need
not be known with great precision. 
 

<DT>• Porosity [m³/m³],
<DD>
determines the
[[Details:MoistureStorageFunction | maximum water content]]
wmax (by
multiplication by ρwater = 1000 kg/m³). 
  
Since most calculations are not sensitive to the exact value of the
maximum water content (you'll rarely encounter water contents above
[[Details:MoistureStorageFunction | free saturation]], it
is usually sufficient to estimate it if no value
is available for the material in question. 
  
The porosity can be estimated from the true density
ρtrue and the bulk
density ρbulk: 
ρbulk = m / Vtot = m / (Vtrue + Vpores) = ρtrue / (1 + Vpores/Vtrue) = ρtrue * Vtrue/Vtot = ρtrue * (1 - Vpores/Vtot) = ρtrue * (1 - porosity), therefore 
  
<CENTER>porosity = 1 - ρbulk / ρtrue.</CENTER>
  
ρtrue can in turn be
estimated from other materials which have the same composition but
different bulk density, if their bulk density and porosity are known.
Example: a cellular concrete brick with ρbulk = 600 kg/m³ and porosity = 0.72 has
ρtrue =
600 / (1 - 0.72) kg/m³ = 2140 kg/m³. The porosity of a
cellular concrete brick with ρbulk = 400 kg/m³ can then be estimated as
porosity = 1 - 400 / 2140 = 0.81. 
  

<DT>• Heat capacity [J/kgK],
<DD>
the specific heat capacity by mass of the dry material. 
  
Using the specific heat capacity by mass has the advantage that this
value only depends on the chemical composition of the material, but
not on its porosity. For example, cellular concrete bricks with
bulk densities of 400 kg/m³ and 600 kg/m³ have the same
specific heat capacity by mass. 
  
To convert into heat capacity by volume (which enters into the
transport equations), WUFI multiplies the mass-specific heat capacity
by the bulk density. 
  
Rough values are 850 J/kgK for mineral materials and 1500 J/kgK for
organic materials. In most cases, these estimates will be sufficient
since hygrothermal simulations usually don't depend very sensitively on
this value.
 

WUFI automatically allows for the additional heat capacity of the
water content, if any. 
  

<DT>• Heat conductivity dry [W/mK],
<DD>
the heat conductivity of the material in dry condition. A
[[Details:HeatConductivityMoistureDependent | moisture-dependent
heat conductivity]] is optional. 
  
Please note that experimentally measured heat conductivities
of vapor-permeable materials may include the effect of vapor
transport with phase change (i.e. water evaporating at one
side of the specimen and condensing at the other side, thus
in effect transporting latent heat without a corresponding
heat flow being conducted across the specimen). Since WUFI
explicitly computes this thermal effect of vapor flow, it
should not be included in the heat conductivity, if possible.
However, it is usually difficult or impossible to separate
this effect out of the measured data. 
  
Furthermore, design values, such as the data given in German
Standard DIN 4108, may already contain the contribution of a
typical water content and, if so, are not strictly dry values. 
If you want to perform the calculation with a constant (i.e. not
moisture-dependent) heat conductivity (for example because you
have no detailed data on the moisture-dependence), you may use
these design values to allow for moisture content at least in
a crude approximation. However, if you explicitly use a table of
[[Details:HeatConductivityMoistureDependent | moisture-dependent]]
heat conductivities, you should make sure
that the value for moisture content = 0 is really the dry value. 
  
On the other hand, hygrothermal simulations (in particular the
resulting moisture contents and distributions) usually don't depend
very sensitively on the precise values of the heat conductivities,
so the difference may be generally negligible unless you are
specifically interested in heat flows. 
  

<DT>• Diffusion resistance factor dry [-]
<DD>the diffusion resistance factor (µ-value) of the
material in dry condition. The µ-value states by how much
the diffusion resistance of the material in question is higher
than that of stagnant air. A
[[Details:DiffusionResistanceFactorMoistureDependent | moisture-dependent µ-value]]
is optional. 
  
The definition of the µ-value and its relation to
permeability are discussed in the topic
[[Details:WaterVaporDiffusion|Water Vapor Diffusion]]. 
  
Please note that even if you do not explicitly use a
[[Details:DiffusionResistanceFactorMoistureDependent|moisture-dependent]]
µ-value, WUFI will treat it as
moisture-dependent for moisture contents above free
saturation wf. WUFI will reduce it in proportion
to the moisture excess over wf, until it reaches
µ=0 at wmax. This reflects - in a first
approximation - the fact that at very high moisture contents
even the larger capillaries become clogged with water and can't
contribute to vapor transport any more.

Details:BasicMaterialData

2009-07-03T08:05:17Z

GauertV:

= Basic Material Data =

These material data constitute an indispensable minimum without
which a calculation is not possible:

<DL>
<DT>• Bulk density [kg/m³],
<DD>
serves to convert the specific heat by mass to the specific heat
by volume. 
  
The bulk density ρbulk
is the ratio of the mass m of the sample and the total volume
Vtot of the sample:
<math>rho_{bulk} = m / V_{tot}</math>. 
<math>ρbulk = m / Vtot</math>. 
The true density ρtrue, by
contrast, is the ratio of the mass of the sample and the volume taken
up by the material matrix only:
ρtrue = m /
(Vtot - Vpores) = m / Vtrue. 
  
The bulk density should be available for virtually every building
material. If not, it can be measured very easily. Since it only affects
the specific heat value entering into the calculation, and hygrothermal
simulations usually don't depend very sensitively on this value, it need
not be known with great precision. 
 

<DT>• Porosity [m³/m³],
<DD>
determines the
[[Details:MoistureStorageFunction | maximum water content]]
wmax (by
multiplication by ρwater = 1000 kg/m³). 
  
Since most calculations are not sensitive to the exact value of the
maximum water content (you'll rarely encounter water contents above
[[Details:MoistureStorageFunction | free saturation]], it
is usually sufficient to estimate it if no value
is available for the material in question. 
  
The porosity can be estimated from the true density
ρtrue and the bulk
density ρbulk: 
ρbulk = m / Vtot = m / (Vtrue + Vpores) = ρtrue / (1 + Vpores/Vtrue) = ρtrue * Vtrue/Vtot = ρtrue * (1 - Vpores/Vtot) = ρtrue * (1 - porosity), therefore 
  
<CENTER>porosity = 1 - ρbulk / ρtrue.</CENTER>
  
ρtrue can in turn be
estimated from other materials which have the same composition but
different bulk density, if their bulk density and porosity are known.
Example: a cellular concrete brick with ρbulk = 600 kg/m³ and porosity = 0.72 has
ρtrue =
600 / (1 - 0.72) kg/m³ = 2140 kg/m³. The porosity of a
cellular concrete brick with ρbulk = 400 kg/m³ can then be estimated as
porosity = 1 - 400 / 2140 = 0.81. 
  

<DT>• Heat capacity [J/kgK],
<DD>
the specific heat capacity by mass of the dry material. 
  
Using the specific heat capacity by mass has the advantage that this
value only depends on the chemical composition of the material, but
not on its porosity. For example, cellular concrete bricks with
bulk densities of 400 kg/m³ and 600 kg/m³ have the same
specific heat capacity by mass. 
  
To convert into heat capacity by volume (which enters into the
transport equations), WUFI multiplies the mass-specific heat capacity
by the bulk density. 
  
Rough values are 850 J/kgK for mineral materials and 1500 J/kgK for
organic materials. In most cases, these estimates will be sufficient
since hygrothermal simulations usually don't depend very sensitively on
this value.
 

WUFI automatically allows for the additional heat capacity of the
water content, if any. 
  

<DT>• Heat conductivity dry [W/mK],
<DD>
the heat conductivity of the material in dry condition. A
[[Details:HeatConductivityMoistureDependent | moisture-dependent
heat conductivity]] is optional. 
  
Please note that experimentally measured heat conductivities
of vapor-permeable materials may include the effect of vapor
transport with phase change (i.e. water evaporating at one
side of the specimen and condensing at the other side, thus
in effect transporting latent heat without a corresponding
heat flow being conducted across the specimen). Since WUFI
explicitly computes this thermal effect of vapor flow, it
should not be included in the heat conductivity, if possible.
However, it is usually difficult or impossible to separate
this effect out of the measured data. 
  
Furthermore, design values, such as the data given in German
Standard DIN 4108, may already contain the contribution of a
typical water content and, if so, are not strictly dry values. 
If you want to perform the calculation with a constant (i.e. not
moisture-dependent) heat conductivity (for example because you
have no detailed data on the moisture-dependence), you may use
these design values to allow for moisture content at least in
a crude approximation. However, if you explicitly use a table of
[[Details:HeatConductivityMoistureDependent | moisture-dependent]]
heat conductivities, you should make sure
that the value for moisture content = 0 is really the dry value. 
  
On the other hand, hygrothermal simulations (in particular the
resulting moisture contents and distributions) usually don't depend
very sensitively on the precise values of the heat conductivities,
so the difference may be generally negligible unless you are
specifically interested in heat flows. 
  

<DT>• Diffusion resistance factor dry [-]
<DD>the diffusion resistance factor (µ-value) of the
material in dry condition. The µ-value states by how much
the diffusion resistance of the material in question is higher
than that of stagnant air. A
[[Details:DiffusionResistanceFactorMoistureDependent | moisture-dependent µ-value]]
is optional. 
  
The definition of the µ-value and its relation to
permeability are discussed in the topic
[[Details:WaterVaporDiffusion|Water Vapor Diffusion]]. 
  
Please note that even if you do not explicitly use a
[[Details:DiffusionResistanceFactorMoistureDependent|moisture-dependent]]
µ-value, WUFI will treat it as
moisture-dependent for moisture contents above free
saturation wf. WUFI will reduce it in proportion
to the moisture excess over wf, until it reaches
µ=0 at wmax. This reflects - in a first
approximation - the fact that at very high moisture contents
even the larger capillaries become clogged with water and can't
contribute to vapor transport any more.

Details:BasicMaterialData

2009-07-03T08:04:43Z

GauertV:

= Basic Material Data =

These material data constitute an indispensable minimum without
which a calculation is not possible:

<DL>
<DT>• Bulk density [kg/m³],
<DD>
serves to convert the specific heat by mass to the specific heat
by volume. 
  
The bulk density ρbulk
is the ratio of the mass m of the sample and the total volume
Vtot of the sample:
<math>ρbulk = m / Vtot</math>. 
<math>rho_{bulk} = m / V_{tot}</math>. 
The true density ρtrue, by
contrast, is the ratio of the mass of the sample and the volume taken
up by the material matrix only:
ρtrue = m /
(Vtot - Vpores) = m / Vtrue. 
  
The bulk density should be available for virtually every building
material. If not, it can be measured very easily. Since it only affects
the specific heat value entering into the calculation, and hygrothermal
simulations usually don't depend very sensitively on this value, it need
not be known with great precision. 
 

<DT>• Porosity [m³/m³],
<DD>
determines the
[[Details:MoistureStorageFunction | maximum water content]]
wmax (by
multiplication by ρwater = 1000 kg/m³). 
  
Since most calculations are not sensitive to the exact value of the
maximum water content (you'll rarely encounter water contents above
[[Details:MoistureStorageFunction | free saturation]], it
is usually sufficient to estimate it if no value
is available for the material in question. 
  
The porosity can be estimated from the true density
ρtrue and the bulk
density ρbulk: 
ρbulk = m / Vtot = m / (Vtrue + Vpores) = ρtrue / (1 + Vpores/Vtrue) = ρtrue * Vtrue/Vtot = ρtrue * (1 - Vpores/Vtot) = ρtrue * (1 - porosity), therefore 
  
<CENTER>porosity = 1 - ρbulk / ρtrue.</CENTER>
  
ρtrue can in turn be
estimated from other materials which have the same composition but
different bulk density, if their bulk density and porosity are known.
Example: a cellular concrete brick with ρbulk = 600 kg/m³ and porosity = 0.72 has
ρtrue =
600 / (1 - 0.72) kg/m³ = 2140 kg/m³. The porosity of a
cellular concrete brick with ρbulk = 400 kg/m³ can then be estimated as
porosity = 1 - 400 / 2140 = 0.81. 
  

<DT>• Heat capacity [J/kgK],
<DD>
the specific heat capacity by mass of the dry material. 
  
Using the specific heat capacity by mass has the advantage that this
value only depends on the chemical composition of the material, but
not on its porosity. For example, cellular concrete bricks with
bulk densities of 400 kg/m³ and 600 kg/m³ have the same
specific heat capacity by mass. 
  
To convert into heat capacity by volume (which enters into the
transport equations), WUFI multiplies the mass-specific heat capacity
by the bulk density. 
  
Rough values are 850 J/kgK for mineral materials and 1500 J/kgK for
organic materials. In most cases, these estimates will be sufficient
since hygrothermal simulations usually don't depend very sensitively on
this value.
 

WUFI automatically allows for the additional heat capacity of the
water content, if any. 
  

<DT>• Heat conductivity dry [W/mK],
<DD>
the heat conductivity of the material in dry condition. A
[[Details:HeatConductivityMoistureDependent | moisture-dependent
heat conductivity]] is optional. 
  
Please note that experimentally measured heat conductivities
of vapor-permeable materials may include the effect of vapor
transport with phase change (i.e. water evaporating at one
side of the specimen and condensing at the other side, thus
in effect transporting latent heat without a corresponding
heat flow being conducted across the specimen). Since WUFI
explicitly computes this thermal effect of vapor flow, it
should not be included in the heat conductivity, if possible.
However, it is usually difficult or impossible to separate
this effect out of the measured data. 
  
Furthermore, design values, such as the data given in German
Standard DIN 4108, may already contain the contribution of a
typical water content and, if so, are not strictly dry values. 
If you want to perform the calculation with a constant (i.e. not
moisture-dependent) heat conductivity (for example because you
have no detailed data on the moisture-dependence), you may use
these design values to allow for moisture content at least in
a crude approximation. However, if you explicitly use a table of
[[Details:HeatConductivityMoistureDependent | moisture-dependent]]
heat conductivities, you should make sure
that the value for moisture content = 0 is really the dry value. 
  
On the other hand, hygrothermal simulations (in particular the
resulting moisture contents and distributions) usually don't depend
very sensitively on the precise values of the heat conductivities,
so the difference may be generally negligible unless you are
specifically interested in heat flows. 
  

<DT>• Diffusion resistance factor dry [-]
<DD>the diffusion resistance factor (µ-value) of the
material in dry condition. The µ-value states by how much
the diffusion resistance of the material in question is higher
than that of stagnant air. A
[[Details:DiffusionResistanceFactorMoistureDependent | moisture-dependent µ-value]]
is optional. 
  
The definition of the µ-value and its relation to
permeability are discussed in the topic
[[Details:WaterVaporDiffusion|Water Vapor Diffusion]]. 
  
Please note that even if you do not explicitly use a
[[Details:DiffusionResistanceFactorMoistureDependent|moisture-dependent]]
µ-value, WUFI will treat it as
moisture-dependent for moisture contents above free
saturation wf. WUFI will reduce it in proportion
to the moisture excess over wf, until it reaches
µ=0 at wmax. This reflects - in a first
approximation - the fact that at very high moisture contents
even the larger capillaries become clogged with water and can't
contribute to vapor transport any more.

Details:BasicMaterialData

2009-07-03T08:03:34Z

GauertV:

= Basic Material Data =

These material data constitute an indispensable minimum without
which a calculation is not possible:

<DL>
<DT>• Bulk density [kg/m³],
<DD>
serves to convert the specific heat by mass to the specific heat
by volume. 
  
The bulk density ρbulk
is the ratio of the mass m of the sample and the total volume
Vtot of the sample:
<math>ρbulk = m / Vtot</math>. 
The true density ρtrue, by
contrast, is the ratio of the mass of the sample and the volume taken
up by the material matrix only:
ρtrue = m /
(Vtot - Vpores) = m / Vtrue. 
  
The bulk density should be available for virtually every building
material. If not, it can be measured very easily. Since it only affects
the specific heat value entering into the calculation, and hygrothermal
simulations usually don't depend very sensitively on this value, it need
not be known with great precision. 
 

<DT>• Porosity [m³/m³],
<DD>
determines the
[[Details:MoistureStorageFunction | maximum water content]]
wmax (by
multiplication by ρwater = 1000 kg/m³). 
  
Since most calculations are not sensitive to the exact value of the
maximum water content (you'll rarely encounter water contents above
[[Details:MoistureStorageFunction | free saturation]], it
is usually sufficient to estimate it if no value
is available for the material in question. 
  
The porosity can be estimated from the true density
ρtrue and the bulk
density ρbulk: 
ρbulk = m / Vtot = m / (Vtrue + Vpores) = ρtrue / (1 + Vpores/Vtrue) = ρtrue * Vtrue/Vtot = ρtrue * (1 - Vpores/Vtot) = ρtrue * (1 - porosity), therefore 
  
<CENTER>porosity = 1 - ρbulk / ρtrue.</CENTER>
  
ρtrue can in turn be
estimated from other materials which have the same composition but
different bulk density, if their bulk density and porosity are known.
Example: a cellular concrete brick with ρbulk = 600 kg/m³ and porosity = 0.72 has
ρtrue =
600 / (1 - 0.72) kg/m³ = 2140 kg/m³. The porosity of a
cellular concrete brick with ρbulk = 400 kg/m³ can then be estimated as
porosity = 1 - 400 / 2140 = 0.81. 
  

<DT>• Heat capacity [J/kgK],
<DD>
the specific heat capacity by mass of the dry material. 
  
Using the specific heat capacity by mass has the advantage that this
value only depends on the chemical composition of the material, but
not on its porosity. For example, cellular concrete bricks with
bulk densities of 400 kg/m³ and 600 kg/m³ have the same
specific heat capacity by mass. 
  
To convert into heat capacity by volume (which enters into the
transport equations), WUFI multiplies the mass-specific heat capacity
by the bulk density. 
  
Rough values are 850 J/kgK for mineral materials and 1500 J/kgK for
organic materials. In most cases, these estimates will be sufficient
since hygrothermal simulations usually don't depend very sensitively on
this value.
 

WUFI automatically allows for the additional heat capacity of the
water content, if any. 
  

<DT>• Heat conductivity dry [W/mK],
<DD>
the heat conductivity of the material in dry condition. A
[[Details:HeatConductivityMoistureDependent | moisture-dependent
heat conductivity]] is optional. 
  
Please note that experimentally measured heat conductivities
of vapor-permeable materials may include the effect of vapor
transport with phase change (i.e. water evaporating at one
side of the specimen and condensing at the other side, thus
in effect transporting latent heat without a corresponding
heat flow being conducted across the specimen). Since WUFI
explicitly computes this thermal effect of vapor flow, it
should not be included in the heat conductivity, if possible.
However, it is usually difficult or impossible to separate
this effect out of the measured data. 
  
Furthermore, design values, such as the data given in German
Standard DIN 4108, may already contain the contribution of a
typical water content and, if so, are not strictly dry values. 
If you want to perform the calculation with a constant (i.e. not
moisture-dependent) heat conductivity (for example because you
have no detailed data on the moisture-dependence), you may use
these design values to allow for moisture content at least in
a crude approximation. However, if you explicitly use a table of
[[Details:HeatConductivityMoistureDependent | moisture-dependent]]
heat conductivities, you should make sure
that the value for moisture content = 0 is really the dry value. 
  
On the other hand, hygrothermal simulations (in particular the
resulting moisture contents and distributions) usually don't depend
very sensitively on the precise values of the heat conductivities,
so the difference may be generally negligible unless you are
specifically interested in heat flows. 
  

<DT>• Diffusion resistance factor dry [-]
<DD>the diffusion resistance factor (µ-value) of the
material in dry condition. The µ-value states by how much
the diffusion resistance of the material in question is higher
than that of stagnant air. A
[[Details:DiffusionResistanceFactorMoistureDependent | moisture-dependent µ-value]]
is optional. 
  
The definition of the µ-value and its relation to
permeability are discussed in the topic
[[Details:WaterVaporDiffusion|Water Vapor Diffusion]]. 
  
Please note that even if you do not explicitly use a
[[Details:DiffusionResistanceFactorMoistureDependent|moisture-dependent]]
µ-value, WUFI will treat it as
moisture-dependent for moisture contents above free
saturation wf. WUFI will reduce it in proportion
to the moisture excess over wf, until it reaches
µ=0 at wmax. This reflects - in a first
approximation - the fact that at very high moisture contents
even the larger capillaries become clogged with water and can't
contribute to vapor transport any more.