[TRNSYS-users] Thermal bridges/Cold bridges in TRNBuild

[Schrade, Johannes]

Dear Anne-Kathrin,

 

as cold bridges are either linear or punctual, the dimension of the resistance for the cold bridge effect must be - to my understanding -either  [hmK/kJ] or [hK/kJ].

If you are analyzing the cold bridges of a building envelope in detail, you would work out the length of connections between adjacent building elements, length of window sills or balcony slabs, the perimeter of windows, etc., so you normally would enter the length of the cold bridge.

If I understand you right, you want to consider the cold bridges by a common additional value (according to DIN 4108-2). In such a case, I would define a resistance for the cold bridge and then I would determine, dependent on the area of the external elements, which are affected by the addition value, the total transmission losses due to cold bridges. Based on the defined resistance and the determined transmission looses, you can calculate the equivalent length of the cold bridge. 

In a previous post, David Bradley addressed that problem with the dimensions of the u-value in the context with cold bridges. He explained that the displayed u-value in the wall type manager is incorrect, however, as the u-value displayed in the wall type manager is not used in the calculation, this error would not affect the results. (see also following mail).

 

Kind regards,

Johannes

  

Johannes Schrade
Abteilung Wärmetechnik

Fraunhofer-Institut für Bauphysik
Nobelstr. 12
70569 Stuttgart

johannes.schrade at ibp.fraunhofer.de <mailto:johannes.schrade at ibp.fraunhofer.de> 
Telefon 0711 / 970-3416
Telefax 0711 / 970-3399
www.ibp.fraunhofer.de/wt/ <http://www.ibp.fraunhofer.de/wt/> 

Johannes Schrade
Department Heat Technology 

Fraunhofer Institute for Building Physics
Nobelstr. 12
70569 Stuttgart, Germany

johannes.schrade at ibp.fraunhofer.de <mailto:johannes.schrade at ibp.fraunhofer.de> 
Phone +49 711 / 970-3416
Fax +49 711 / 970-3399
www.ibp.fraunhofer.de/wt/ <http://www.ibp.fraunhofer.de/wt/> 

 

Mattieu,

  I think that the wall type manager is where the incorrect units are 

displayed. My understanding is that a coldbridge does not have any 

thickness but it does have a length. For example, if you want to make a 

coldbridge to represent the lack of insulation where two exterior walls 

are joined, you would define a coldbridge that has the length of the 

joint. The resistance you enter should be in kJ/h.m.K (where the length 

is the length of the bridge). The error in TRNBuild is that the wall 

type manager should change the units of u-value when a coldbridge wall 

is displayed. Note that since the u-value displayed in the wall type 

manager is not actually used in calculation, that this error should not 

affect your results.

Kind regards,

David

 

 

matthieu duclos wrote:

> Dear Trnsys Users,

> 

> I have a problem about a bug for thermal bridge, I find an answer in 

> the archives but ...:

> 

> 

> Hi Nicola,

> 

> nicola wrote:

> > Dear all,

> > I'm modelling a wall wit a thermal bridge effect.

> > I found a bug in TRNBuilt :

> > 1. If I put the value of resistence equal to xxx (hmK/kJ) in the layer

> > manager, the program create a wall with a U-value expressed in kJ/h

> > m^2K and a resistence equal to xxx in hm^2k/kJ!!!

> Thanks for finding this bug. I think it is only a problem of displaying

> the units. The resistance should be entered in h m^2K /kJ, and not h m

> K /kJ. When you check on the 'Layer type manager', the resistance is

> shown in h m^2K /kJ.

> > 2. the u-value of a wall with thermal bridge effect is lower than the

> > same wall without thermal bridge effect.

> The u-value displayed in the 'Wall type manager' is calculated by adding

> two reference heat transfer coefficients to the wall (7.7 and 25 W/m^2 

> K).

> 

> Best regards,

> 

> Diego

> 

> 

> ... in "Walls" when I choose a coldbridge I can put the value for 

> length in m , not a surface in m^2.

> 

> What is the solution?

> If the solution is all in m^2, how can I change a linear thermal 

> bridge to surface thermal bridge?

> 

> Thanks in advance,

> 

> Matt

> 

 

 

Von: trnsys-users-bounces at cae.wisc.edu [mailto:trnsys-users-bounces at cae.wisc.edu] Im Auftrag von Anne-Kathrin.Albrecht at ise.fraunhofer.de
Gesendet: Montag, 16. Juli 2012 16:46
An: trnsys-users at cae.wisc.edu
Betreff: [TRNSYS-users] Thermal bridges/Cold bridges in TRNBuild

 

Dear Users, 

I know that this problem has been discussed before so I know that there is a bug, but am not sure how to handle it: 

1. When you add a new massless layer with coldbridge effect you have to enter the "resistancy" in hmK/(kJ). Do you actually have to enter the resistancy, which would be in hm²K/(kJ) or does TRNBuild asks for the conductivity, which would be in hmK/(kJ)? 

2. The layer type manager shows the same value for "resistancy" as typed in before in hm²K/(kJ). It´s just a problem of showing the units right, isn´t it? So is it actually the resistancy that is shown in both cases? 

3. What is meant by the length? Is it the part where the walls connect or is it the edge length? Independently of the entered value of the length, the u-value doesn´t change. How does TRNBuild calculate with this value? 


I would like to add a common used factor of 0,05 W/(m²K) for all surface areas. How do I implement that? 


Thank you very much for you help in advance, 

Anne

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