[TRNSYS-users] Coldbridge effect and mixed geometry model

Wed Mar 19 08:42:52 PDT 2014

Dear Jochen,

Thanks again for your answer.

As regards this problem, I have been trying different methods and I have two other doubts. I hope you can help me:

1)      If I draw a small surface embedded in the original method, I can import the .idf model to TrnBuild and define it as Coldbridge. It seems that I have no problems generating ism and vfm files, but I have two other problems:

a.       When I import the model an error window of TrnBuild appears, with the message “Wallarea<=Windowarea” for all the zones with windows where I draw the small surface. If I accept this message, I can save, continue and simulate, but I would like to understand the problem, because the wall I drew does not include any window..

b.      When I define the new wall as a Coldbridge, I can edit the thermal, absorptance, and emissivity characteristics of the wall, but I cannot put the correct length of the coldbridge. The problem (I described it in the previous mail, even if I was proposing another – incorrect - method) is that it imports the area and not the length. So, even the voice is “length”, the value is the area of the little surface. I am thinking that the only way to change it is to change this value manually by editing the text of the .b17 file. Is it the only way?

2)      When I add a Coldbridge (from the zone window and not from the Wall Type Manager) I have to put the resistance value in hmK/KJ. This is the “ᴪ” value in the definition of coldbridge. Should this value include inside and outside surface (or … linear?) resistance?

From the window “New Wall Type with Coldbridge Effect” it seems that it does not include them.
                In fact, if I open the Wall Type Manager, after creating the Coldbridge in the way I said, I can see the new coldbridge wall, defined as a massless wall, with a U which includes Rse and Rsi.
This theme confuses me a bit, also because I have just read a message here in the forum, where David Bradley explains that the displayed U-value in the wall type manager is incorrect and it is not used in the calculation.
Here is the reference:
https://mailman.cae.wisc.edu/pipermail/trnsys-users/2012/010237.html

Thanks for the help,
Best regards.

Verdiana Russo

De: trnsys-users-bounces at cae.wisc.edu [mailto:trnsys-users-bounces at cae.wisc.edu] En nombre de hotline
Enviado el: miércoles, 12 de marzo de 2014 16:16
Para: 'TRNSYS users mailing list at the Solar Energy Lab, UW-Madison'
Asunto: Re: [TRNSYS-users] Coldbridge effect and mixed geometry model

Dear Verdiana,

I’m sorry I was pretty unexact in my last explanation. There are two ways to integrate the coldbridge,
and keep the possibility of using the detailed radiation computation.

1.       You can draw a small surface embedded in your original geometry and define it as a

massless surface (wall), with properties, which represents your coldbridge.

(That’s what I’ve recommended to you in my last mail. My colleague told me, that you might run

into trouble with generating the ism, vfm matrices with this method).

2.       Or, you adapt the U-Value of your original wall

Uvalue = (Uwall*Area + Coldbridge_1 x L_1 + Coldbridge_2 x L_2 + ...

    +  Coldbridge_i x L_i)/Area

Regards

__________________________________________________________________________________________________

Jochen Lam
TRNSYS Software Team

Transsolar Energietechnik GmbH
Curiestraße 2
70563 Stuttgart
Fax:        +49 711 67976-11
Email:    jlam at transsolar.com<mailto:jlam at transsolar.com>
Web:      www.trnsys.de<http://www.trnsys.de>

Von: trnsys-users-bounces at cae.wisc.edu<mailto:trnsys-users-bounces at cae.wisc.edu> [mailto:trnsys-users-bounces at cae.wisc.edu] Im Auftrag von Verdiana Russo
Gesendet: Mittwoch, 12. März 2014 14:43
An: TRNSYS users mailing list at the Solar Energy Lab, UW-Madison
Betreff: Re: [TRNSYS-users] Coldbridge effect and mixed geometry model

Dear Jochen,

Thank you for your answer.

As regards the shm file, I checked, and it’s ok, I understood. Thanks, this point was not so clear to me.

As regards the definition of cold bridges, I have some other questions. Perhaps you can help me.

-          As you say, I use this method: I draw a wall in a thermal zone in SketchUp and I re-import the model in TrnBuild. When I define the wall as a cold bridge, it changes automatically the voice “area” of the wall to the voice “length”, as it is a cold bridge. But the value is the same of the area of the wall I drew in SketchUp. This means that the way to put the correct length is to draw in SketchUp a wall with this length x 1m of width, isn’t it?

-          May I put the new wall (which will be defined as cold bridge) everywhere in the space of a thermal zone? For example, if I draw a wall corresponding to the cold bridge of a pillar/floor in front of the position of the pillar/floor, at a certain distance from the facade’s wall, does it affect as a shading element to the wall or not? And in any case, what is the better place to draw the wall?

I attach images to help you to visualize my question.

-          Finally, is there a way to define punctual cold bridges?

Thank you very much and best regards,

Verdiana

De: trnsys-users-bounces at cae.wisc.edu<mailto:trnsys-users-bounces at cae.wisc.edu> [mailto:trnsys-users-bounces at cae.wisc.edu] En nombre de hotline
Enviado el: martes, 11 de marzo de 2014 15:06
Para: 'TRNSYS users mailing list at the Solar Energy Lab, UW-Madison'
Asunto: Re: [TRNSYS-users] Coldbridge effect and mixed geometry model

Dear Verdiana,

1)      To add a new wall and keeping the possibility of using the detailed radiation computation. You have to export the

TRNBuild model to an idf File and add the wall in SketchUp. Afterwards you can re-import and define

the wall as a coldbridge.

2)      The shm file is used, when it exists (and when it is named as your b17 file) , no matter if you choose the 3D Mode, the mixed mode or manual mode. You can check in the list file if the shm file is used, this message will occure.

*** Notice at time        :         0.000000

    Generated by Unit     :    14
    Generated by Type     :    56

    Message               : Shading mask file *.shm  for external windows exists and will be used.

The difference is that vfm and ism matrices can’t be used in the mixed mode.

Regards
__________________________________________________________________________________________________

Jochen Lam
TRNSYS Software Team

Transsolar Energietechnik GmbH
Curiestraße 2
70563 Stuttgart
Fax:        +49 711 67976-11
Email:    jlam at transsolar.com<mailto:jlam at transsolar.com>
Web:      www.trnsys.de<http://www.trnsys.de>

Von: trnsys-users-bounces at cae.wisc.edu<mailto:trnsys-users-bounces at cae.wisc.edu> [mailto:trnsys-users-bounces at cae.wisc.edu] Im Auftrag von Verdiana Russo
Gesendet: Montag, 10. März 2014 17:00
An: trnsys-users at cae.wisc.edu<mailto:trnsys-users at cae.wisc.edu>
Betreff: [TRNSYS-users] Coldbridge effect and mixed geometry model

Dear TRNSYS Users,

I have two questions about building simulation.

1)      I would like to introduce some coldbridge effects in a building model, created with Trnsys3D-SketchUp.

As I see, a way to do it is to add a new wall to the zone, and define it as Coldbridge.

To do this, the program asks me to change the geometry model from “3D” to “manual” or “mixed”.

But in this way I lose the possibility to simulate with detailed internal and external radiation mode.

Do you know if there is another way to consider coldbridge effects, which functions with detailed radiation mode?

Is there anyone who tried to do it?

2)      In Volume 5 of the TRNsys Manual the difference between “3D”, “manual” and “mixed” geometry mode is explained.

In “mixed” mode it says that only detailed external shading is considered.

As I understand from this, if I use this mode, I should need the shading matrix file to run the simulation and to consider external shading.

But I tried to run the simulation pulling out the .shm file from the folder where the .b17 file is, and the simulation runs without errors.

So I think that it does not need .shm file to function.

I pulled out the .ism, .shd too, and I see that it does not use them too.

So, my question is: how does “mixed” mode consider detailed external shading?

Thanks and best regards,

Verdiana Russo
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