[TRNSYS-users] Internal wall modelling

Tue Feb 26 05:09:53 PST 2019

Dear Marion,

Thank for your response.

I'm surprised that equivalents results with (a) and (b) are get with 2*S 
area, as it is not what I observe (with an hypothetical zone only having 
one window and one internal wall):

(plots = temperature of the zone over the time)

- (a), area = 2*S ['T_zone_PI_2'] and (b), area = 2*S ['T_Zone BI_2'] 
with the same symetric composition :

Results are actually very similar, but error seems to regularly increase 
over the time.

- (a), area = 2*S, half composition ['T_zone_PI_2_divI'] and (b), area = 
S, whole composition ['T_Zone BI_1'] :

Results are nearly identical.

- (a), area = 2*S ['T_zone_PI_2'] and (b), area = S ['T_Zone BI_1'] with 
the same composition:

(a) thermal mass is clearly higher than (b)

By the way, I'm not sure to understand why (b) requires 2*S. For a 
'classic' wall having a area S, the thermal flux of the inside face 
(phi_i) goes to the inner zone (P_i=phi_i*S) and the thermal flux of the 
outside face (phi_o) goes to the outer zone (P_o=phi_o*S). When we 
defined this wall 'boundary/indentical', as the inner and outer zone is 
the same, it automatically receives P_i + P_o via both (inside and 
outside) faces (2*S), whitout having to set a 2*S area. Unless the 
implementation is different with these options, as you seem to indicate 
(parametrizing the global exposed area (2*S)). In this case, is it sure 
that the surface is not accounted for 2 times (due to inside and outside 
exposure and using 2*S area)?

Regards,

Le 26/02/2019 à 11:43, Marion Hiller via TRNSYS-users a écrit :
>
> Dear Loïc
>
> I have to confess that this is a little confusing.
>
> I would have loved to remove the surface category “internal” 
> completely. However, due to backwards compatibility it remained.
>
> I recommend to use category 'boundary' and the boundary condition 
> 'identical' because there it is more clear what is calculated.
>
> Please find my comments below:
>
> I noticed that the first option implies to consider the total exposed 
> surface (both sides) for the area parameter, unlike the second one. I 
> guess that in (a) the middle of the wall is assumed adiabatic in order 
> to model only a half wall but with an area 2 times higher. If this is 
> correct, it is implicitly assumed that the internal wall composition 
> is symetric. By the way, I found that the wall balance is not null 
> otherwise.
>
> Is the (a) modelling really only concern symetric composition?
> => Yes, for the option “internal” the composition has to be internal
>
> Nonetheless, when I compare (a) with a 2*S area and (b) with a S area, 
> for a symetric composition, the results are not exactly the same. I 
> succeed having same results by setting the composition of (a) with 
> only the half of it (from a face to the middle).
>
> => For having (a) and (b) giving similar results you have to use for 
> (b) the same exposed area to the airnode/zone as for (a) (area =2*S).
>      Otherwise the airnode/zone doesn’t have “access” the same amount 
> of thermal mass. This results in different heat fluxes to the inner 
> surface
>     node.
>
> So, the (a) modelling need half composition?
>
> => No,  (b) requires double area (see above).
>     Have in mind that “Internal” means that both sides of the 
> construction are facing towards the zone. You have to define the total 
> construction
>    for having the correct mass. The program divides the construction 
> itself.
>
> Regards,
>
> Marion
>
> *-----------------------------------------------------------------------------------------------------------------------------------------------------------*
>
> *Dipl.-Ing. Marion Hiller **
> **TRANSSOLAR Energietechnik GmbH *
> *Stuttgart - Munich - New York - Paris ***
>
> *t: +49.711.67976.0 <tel:%2B49.711.67976.27> f: +49.711.67976.11 
> <tel:%2B49.711.67976.11>*
>
> *www.transsolar.com/ <http://www.transsolar.com/>**
>
> **KlimaEngineering - Technologien für energieeffizientes Bauen und 
> Nutzerkomfort in Gebäuden **
> **Transsolar Energietechnik GmbH, Curiestrasse 2, 70563 Stuttgart *
>
> *Amtsgericht Stuttgart - HRB 23347**/ Steuernummer: 99073/00911 / 
> USt-IdNr.: DE 152272639**
> Geschäftsführer: Matthias Schuler, Thomas Auer, Stefan Holst, Dieter 
> Schnelle *
>
> *Von:*TRNSYS-users <trnsys-users-bounces at lists.onebuilding.org> *Im 
> Auftrag von *Loïc Frayssinet via TRNSYS-users
> *Gesendet:* Donnerstag, 21. Februar 2019 15:35
> *An:* trnsys-users at lists.onebuilding.org
> *Cc:* Loïc Frayssinet <frayssinet at enertech.fr>
> *Betreff:* [TRNSYS-users] Internal wall modelling
>
> Dear all,
>
> I was wondering if it is similar to model an internal wall as a wall :
>
> (a) with the category 'internal' or
> (b) with the category 'boundary' and the boundary condition 'identical'
>
> I noticed that the first option implies to consider the total exposed 
> surface (both sides) for the area parameter, unlike the second one. I 
> guess that in (a) the middle of the wall is assumed adiabatic in order 
> to model only a half wall but with an area 2 times higher. If this is 
> correct, it is implicitly assumed that the internal wall composition 
> is symetric. By the way, I found that the wall balance is not null 
> otherwise.
>
> Is the (a) modelling really only concern symetric composition?
>
> Nonetheless, when I compare (a) with a 2*S area and (b) with a S area, 
> for a symetric composition, the results are not exactly the same. I 
> succeed having same results by setting the composition of (a) with 
> only the half of it (from a face to the middle).
>
> So, the (a) modelling need half composition? If yes, why non-symetric 
> compositions causes balance divergences?
>
> Regards,
>
> -- 
> *Loïc FRAYSSINET *
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at lists.onebuilding.org
> http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org

-- 
*Loïc FRAYSSINET *

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20190226/711fb6f8/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: jbadolnppgcgnkck.png
Type: image/png
Size: 17631 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20190226/711fb6f8/attachment-0006.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: icnobkgcccgilopd.png
Type: image/png
Size: 19803 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20190226/711fb6f8/attachment-0007.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: bgepdjpppgbemong.png
Type: image/png
Size: 21235 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20190226/711fb6f8/attachment-0008.png>