SebSta: hat „FAQ General:WhyNever100RHintheComponent“ nach „FAQ:General:WhyNever100RHintheComponent“ verschoben

2013-06-13T12:30:15Z

hat „FAQ General:WhyNever100RHintheComponent“ nach „FAQ:General:WhyNever100RHintheComponent“ verschoben

← Nächstältere Version	Version vom 13. Juni 2013, 14:30 Uhr
(kein Unterschied)

Len: Die Seite wurde neu angelegt: = (16): Why Never 100% RH in the Component? = I'm familiar with steady-state water vapor diffusion calculations (in particular, the Glaser method described in Germa...

2008-10-06T08:44:16Z

Die Seite wurde neu angelegt: = (16): Why Never 100% RH in the Component? = I'm familiar with steady-state water vapor diffusion calculations (in particular, the Glaser method described in Germa...

Neue Seite
= (16): Why Never 100% RH in the Component? =

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%.


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).


That's because a relative humidity of 100% would correspond to a
[[Details:MoistureStorageFunction | moisture content]]
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.


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.


Furthermore, real materials (as opposed to Glaser) usually have some
[[Details:LiquidTransportCoefficients | capillary conductivity]] 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.


Of course, you may 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...

FAQ:General:WhyNever100RHintheComponent - Versionsgeschichte

SebSta: hat „FAQ General:WhyNever100RHintheComponent“ nach „FAQ:General:WhyNever100RHintheComponent“ verschoben

Len: Die Seite wurde neu angelegt: = (16): Why Never 100% RH in the Component? = I'm familiar with steady-state water vapor diffusion calculations (in particular, the Glaser method described in Germa...