SebSta am 13. Juni 2013 um 12:46 Uhr

2013-06-13T12:46:03Z

← Nächstältere Version		Version vom 13. Juni 2013, 14:46 Uhr
Zeile 7:		Zeile 7:
	<P>		<P>
	If you model the ventilation gap as an		If you model the ventilation gap as an
	[[AirLayers \| air layer]] in WUFI, it is indeed treated as a		[[Details:AirLayers \| air layer]] in WUFI, it is indeed treated as a
	closed air layer without connection to the exterior air. The effect of inner		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		convection on heat and moisture transport across the air layer is allowed for
	(as a first approximation) by use of		(as a first approximation) by use of
	[[AirLayers \| effective]]		[[Details:AirLayers \| effective]]
	[[Details:Material \| heat conductivities]] and		[[Details:Material \| heat conductivities]] and
	[[Details:Material \| vapor diffusion resistance factors]].		[[Details:Material \| vapor diffusion resistance factors]].

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

2013-06-13T12:34:26Z

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

← Nächstältere Version	Version vom 13. Juni 2013, 14:34 Uhr
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Len: Die Seite wurde neu angelegt: = (19): Ventilated Curtain Walls = 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 the...

2008-10-06T09:31:27Z

Die Seite wurde neu angelegt: = (19): Ventilated Curtain Walls = 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 the...

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= (19): Ventilated Curtain Walls =

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.


If you model the ventilation gap as an
[[AirLayers | air layer]] 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
[[AirLayers | effective]]
[[Details:Material | heat conductivities]] and
[[Details:Material | vapor diffusion resistance factors]].


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. 
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
[[Details:RainWaterAbsorptionFactor | rain absorption factor]] = 0). 
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.


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.


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. 
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 as=0.6 and an
effective heat transfer coefficient of a=19 W/m²K.
The effective absorptivity is roughly identical with the real absorptivity
(for red roof tiles), while the effective a is slightly
higher than the usual standard value of 17 W/m²K. 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. 
The question to which extent this isolated result can be generalised could only
be answered by more extensive comparisons with measurements.


[1] H.M. Künzel: Außen dampfdicht, vollgedämmt? - Die rechnerische
Simulation gibt Hinweise zu dem Feuchteverhalten außen dampfdichter
Steildächer. bauen mit holz 8/98, S. 36-41.

FAQ:General:VentilatedCurtainWalls - Versionsgeschichte

SebSta am 13. Juni 2013 um 12:46 Uhr

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

Len: Die Seite wurde neu angelegt: = (19): Ventilated Curtain Walls = 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 the...