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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
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@cae.wisc.edu [mailto:trnsys-users-bounces@cae.wisc.edu] Im Auftrag von Anne-Kathrin.Albrecht@ise.fraunhofer.de Dear Users, |