[TRNSYS-users] Fwd: Error creating the wall transfer function coeffients
hiller at transsolar.com
Thu Nov 22 23:51:17 PST 2012
a cavity of 1m should definitely be modelled by a zone!
The “edge” effects shouldn’t be neglected.
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.:
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
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?
2012/11/21 Benoit Delcroix <benoit.delcroix at polymtl.ca>
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
Le 2012-11-21 04:27, 王洋 a écrit :
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.
2012/11/20 Benoit Delcroix <benoit.delcroix at polymtl.ca>
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).
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
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!
2012/11/17 Benoit Delcroix <benoit.delcroix at polymtl.ca>
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,
Le 2012-11-17 14:43, trnsys-users-request at cae.wisc.edu a écrit :
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