[TRNSYS-users] Fwd: Error creating the wall transfer function coeffients

Thu Nov 22 23:51:17 PST 2012

Wang,

a cavity of 1m should definitely be modelled by a zone! 

The “edge” effects shouldn’t be neglected.

Marion

Dipl.-Ing. Marion Hiller 
TRANSSOLAR: KlimaEngineering - Technologien für energieeffizientes Bauen
und Nutzerkomfort in Gebäude 
Munich - New York - Stuttgart + 49.711.67976.0 

Transsolar Energietechnik GmbH, Curiestrasse 2, 70563 Stuttgart 
Amtsgericht Stuttgart - HRB 23347, Steuernummer 99073/00911, USt-IdNr.:
DE152272639

Geschäftsführer: Dipl.Ing. Matthias Schuler, Dipl.Ing. Thomas Auer,
Dipl.Phys. Stefan Holst, Prof. Dipl.-Ing. Bleicher 

  _____  

Von: 王洋 [mailto:wanghongyang1767 at gmail.com] 
Gesendet: Donnerstag, 22. November 2012 16:25
An: Benoit Delcroix; trnsys-users
Betreff: Re: [TRNSYS-users] Fwd: Error creating the wall transfer
function coeffients

Dear Benoit,

Thanks for your patient reply!
I saw your attached figure. But there is a new problem. As I said for my
first email, my air layer is about 1m, however, this figure's maximal
thickness of air is only 300 mm. therefore, Whether or not it is right
when I still use 4.5 W/m2K your figure said as the air layer's U-value?

thanks!
Br.

yang wang

2012/11/21 Benoit Delcroix <benoit.delcroix at polymtl.ca>

Hi, 

The new value is including convection, radiation and conduction (and not
only conduction). There is a reference in English in 2009 ASHRAE
Handbook - fundamentals (chapter 26). The reference I have is in French
(a Belgian regulation on energy performance of buildings). I have
attached a jpg file with the table if you want. The first column is the
thickness (in mm). The 3 next are depending on the heat flux direction
(respectively upward, horizontal and downward). And the values in the
table are resistances in m²K/W. The reference in ASHRAE is a little bit
more complicated. 

Best,

Benoit

Le 2012-11-21 04:27, 王洋 a écrit :

   Dear Benoit,

   Thanks for your reply!

   I did as you said, i.e. I changed the air U-value from 0.09252 W/m2K
   into 4.65 W/m2K. Then the min. timebase 2 hours can work. But I'd
   like to ask you why we should set this value 4.65 W/m2K? Could you
   please tell me which reference literature said? Because I checked the
   air conductivity as 0.09252 kJ/hmK from the literature.

   Thanks!
   Br.
   yang wang

   2012/11/20 Benoit Delcroix <benoit.delcroix at polymtl.ca>

   Hello,

   To me, I think you should set your air layer as a resistive layer and
   set the air U-value to 4.55 - 4.65 W/(m²K) (if there is no
   ventilation in the basement). And normally, afterwards, you should be
   able to decrease the timebase value (normally 1 hour should be
   possible). If you want less, split the heaviest walls with an active
   layer (probably the roof and groundfloor walls).

   Best,

   Benoit   

   Le 2012-11-19 04:31, 王洋 a écrit :

      Dear Leen, Jean, Marion, Benoit and others,

      Many thanks for your reply!

      I checked my Wall's thickness and thermal property etc. again. Why
      needs it 9 hours as the timebase? I think maybe it is due to my
      Ground floor (it is the basement's floor of the building) which
      includes about 0.99 m's Air Layer.
      When I changed it into 0.1 m, the min. timebase 2.5 hours can work
      without the ERROR:Error creating the wall transfer function
      coeffients.

      Therefore, I'd like to ask you, 
      1) Is it normal for TRNBuild setting how large the timebase is
      maximally? 5 hours or others?
      2) How to solve this problem of the ground floor with about 0.99
      m's Air Layer? But our building project indeed has
      the ground floor with about 0.99 m's Air Layer. I can't reduce it
      into 0.1m? Is the only way to  try the active layer approach of
      The group of Michael Kummert in Montreal?   

      Please see the Attached INF file.

      Thanks in advance!
      Br.

      wang

      2012/11/17 Benoit Delcroix <benoit.delcroix at polymtl.ca>

      Hello,

      I'm one of the students of Michaël Kummert working on a new method
      to generate the tranfer functions. I thing I can help you for your
      problem. As Leen said, TRNSYS is unable to generate the transfer
      functions coefficients for a heavy and insulated wall with a low
      timebase. In the TRNBuild project, you can modify that value and
      increase it to allow TRNSYS to generate the transfer functions.
      Actually, TRNSYS is unable to generate the transfer function as
      soon as the Fourier number of the wall (thermal diffusivity *
      timebase / thhickness²) is lower than 0.0005. To check that,
      TRNBuild make the sum of one of the coefficients series (a, b or
      c). The 3 sums are equal and means, according to TRNBuild (I don't
      personally think so...but it's like this), the Fourier number. 

      As Leen said, it exists a trick. You can use an active layer to
      split the wall in 2 and then forcing TRNSYS to generate 2 series
      of transfer functions coefficients for the same wall. As the 2
      parts are thinner, you could use a better timebase value. When you
      insert the active layer in the wall, try to split the layer with
      the lowest Fourier number. And then to insert the active layer,
      use the expert mode that allows you to insert an equivalent
      conductivity. Insert the biggest value you can. Like that, the
      active layer is negligible at the thermal point of view. Actually,
      the active layer is acting as a mini-zone to split the wall. It is
      a little tricky but it works...before having better solution.

      Good luck for your project and have a nice week-end,

      Benoit   

      Le 2012-11-17 14:43, trnsys-users-request at cae.wisc.edu a écrit :

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