[TRNSYS-users] Air layer in Trnbuild

[David BRADLEY]

Marko,
  The reason that the "airlayer" material in the TRNBuild libraries is 
massless and has no thickness is that narrow air gaps (i.e. airgaps with 
little or no convection in them) can be assumed to provide thermal 
resistance in the wall. When you have a wide air gap then the convection 
within that airgap becomes important and you cannot correctly account 
for it as though it were part of the wall. What I would recommend you do 
is to treat that 70cm air gap as though it were one or more airnodes 
separated from the ambient and the conditioned space by "walls" that 
consist only of your polyester foil (treated as massless layers offering 
only a thermal resistance). You can set the convection coefficients on 
the inside of those two layers as computed internally by Type56. This is 
probably still not an ideal treatment of the situation either but in my 
opinion it is more correct than lumping the air gap into the wall.
kind regards,
  David


On 4/29/2015 1:58 PM, Marko Mancic wrote:
> Hi Trnsys users,
>
> I am trying to create a model of a lightweight contruction sport hall, 
> which consists of two leyers of special Polyester foils, and a 70cm 
> air layer between. In reality, the construction is streched and held 
> in place by a wood sceleton.
>
> I have noticed, that whichever air layer is chosen from the library, 
> it is modelled as massless, and the tickness is 0.
>
> How can I change the tickness of the Air layer?
>
> In addition, I get the following error messages when I try to save the 
> project "error when trying to create wall transfer coefficients"
> " unable to find root, after indication that root exists"
> "Maybe time base is to small"
>
> What could be the couse of the error I am getting?
>
>
> Thank you for helping!
>
>
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> TRNSYS-users at lists.onebuilding.org
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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