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

[王洋]

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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>>    1. Re: Fwd: Error creating the wall transfer function	coeffients
>>       (leen peeters)
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