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

[王洋]

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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>>>    1. Re: Fwd: Error creating the wall transfer function	coeffients
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>>
>>
>
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