results of thermal bridges uninsulated building

[Arquinea AyD]

I'm Amaia from the Arquinea studio. We are working with the Therm program to calculate the thermal bridges of an existing building before and after energetically rehabilitating its façade. The results we obtain, for example, in the case of thermal bridge of a non-insulated façade with slabs are negative, which either we do not know how to interpret or we have calculated it incorrectly.

Is there an example of thermal bridge calculation in a non-insulated building? Or is it correct to give negative values?

Thanks in advance

[Robin Mitchell]

can you provide one or more of your files? 

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Robin Mitchell

Building Technology and Urban Systems Division
Energy Technologies Area
Lawrence Berkeley National Laboratory

[Arquinea AyD]

Of course, I attach the detail of the thermal bridge of the façade with slabs before and after insulating the façade from the outside and also the excel to get the results. Therm version is 7.8.74.0. Thank you so much

[Robin Mitchell]

What results are negative? When I run the attached files, I see reasonable results.

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[Arquinea AyD]

Hello, I am attaching a .pdf where I try to explain the issue better.

Thank you

[Zugur Rakhmanov]

Hello Arquinea,
Where do you give the 'Transmitancia térmica's' values from?

Kind regards

Zugur

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[in...@arquinea.es]

Hello,
I have obtained the thermal transmittance of the façade by creating an enclosure in the official program of energy certificates of the Spanish regulations, I will send you an image.

I just did the test of removing the U from the façade in Therm with the same section and it gave me a very different value, 1.28 W/m2k, and the calculation for the Bridge would come out 0.42 W/mk, which is somewhat closer to the 1.51W/mk of reference but still with a lot of difference.

I send you the files, thank you.

Un saludo,

¡Síguenos en las redes sociales y visita nuestra web!

 www.arquinea.es

C/Mª Díaz de Haro 68, 2ª - Of.3
48920 - Portugalete, Bizkaia
946 526 095  /  656 329 671

[D. Charlie Curcija/LBNL]

I am not sure where U=1.69 comes from. Since I don't speak Spanish, I don't quite get the meaning of various quantities, but from EN 10077 standard, Psi value is calculated by subtracting heat flow for actual glazing from heat flow for insulating panel. From this example, Psi value might be calculated by subtracting 2D heat flow (with thermal bridge) from 1D heat flow for wall element without the thermal bridge. So, going back to U=1.69, is that the U-factor for the same wall section, but without thermal bridge? Or is U=1.28 correct value?

In general, as far as 2D calculations are concerned, THERM gives pretty darn correct answer.

Charlie

[Ale]

Hola Amaia,

the value you obtained with your program considers only conduction, then you have to consider the convection on the external and internal surface so you would have:

Rtotal = Rse + Rc + Rsi = 1/hse + Rc + 1/hsi = 0.04 + 0.59 + 0.13 (vertical walls) = 0.76 m2K/W

at the end you would have U = 1.31 W/m2K (that is closed to the value that you got with Therm, that is correct).

Hope this will help you.

Saludos,

Alessia

[in...@arquinea.es]

 Hello, everyone,

then I will calculate the thermal bridge with the U of the facade extracted from THERM and also the heat flow.

Thank you very much to everyone for your help.

Un saludo, Amaia

Un saludo,

¡Síguenos en las redes sociales y visita nuestra web!

 www.arquinea.es

C/Mª Díaz de Haro 68, 2ª - Of.3
48920 - Portugalete, Bizkaia
946 526 095  /  656 329 671

El mar, 9 abr 2024 a las 0:25, Zugur Rakhmanov (<zugur.r...@gmail.com>) escribió: