[TRNSYS-users] transfer function

[David BRADLEY]

Leen,
   The reason that thick, highly insulated walls give you a problem is 
that TRNBuild generates the first 20 coefficients of the transfer 
function that describes the thermal response of the wall. The 
coefficients correspond to discreet intervals of time starting with the 
present and moving backwards by steps of the timebase specified in 
TRNBuild. The default is an hour so it is my understanding that TRNBuild 
looks back at 20 hours worth of transfer function coefficients to 
determine whether the numerical stability of the wall model has been 
met. In very massive walls, 20 hours might not be a long enough time 
interval to adequately describe the wall's response. You can try to 
increase the wall timebase to 2 hours in order to extend how far back 
the wall's response is considered. However, in my experience, this can 
cause problems with the less massive walls in the same project (which 
sometimes have to be changed over to massless walls since their response 
time is now too short to be adequately represented with a 2 hour timebase.
Best,
  David


On 4/14/2012 17:27, leen peeters wrote:
> Dear all,
> I am trying to model an old house which will be imporved to a very 
> good house (www.zehr .be). The existing brick walls consist of 33 cm 
> of brick, no air cavity or insulation. One wall will be packed 
> with 6cm VIP, the remainder will be packed with a 30 cm layer of 
> insulation (lanba of 0.038 W/mK).
> However modeling that, I ran into problems with the stability of the 
> transfer function, shoudl that I had to tune my capacities and 
> densities in order to end up with something that was accepted for 
> calculating the transferfunction.
> Can anyone explain me the logic of these warming messages and the 
> reason why thick highly insulated walls cause an issue? I trid 
> splitting one layer into two, but that did not resolve the problems...
> leen
>
>
> _______________________________________________
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> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
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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