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

Fri Nov 23 00:48:43 PST 2012

Dear Marion,

Thanks for your email!

But all those air cavity with 1 m thickness is not connected together. They
are separated into 11 parts due to 11 zones in the basement.
Do you mean like this situation all those air cavity still should be
modelled by a zone?

Thanks!
Br.
yang wang

2012/11/23 Marion Hiller <hiller at transsolar.com>

> ** ** **
>
> 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
>
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> Amtsgericht Stuttgart - HRB 23347, Steuernummer 99073/00911, USt-IdNr.:
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> Dipl.Phys. Stefan Holst, Prof. Dipl.-Ing. Bleicher *
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>  ****
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>  ------------------------------
>
>
> *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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