THERM 6: calculation of U-Frame at corner detail

[Christian Rehner]

Hello,

 

 

I calculate u-factor-values of our curtain wall units.

 

I have a problem with the calculation of a u-factor of the frame at a corner detail (see attached pdf file of the vertical section).

 

I want to calculate an average u-factor of an building element with the marked U-factor areas with Therm 6 (Uc, U edge and U frame at page 1)

At the inner site I can just assign a small area for the U-Factor surface of the frame.

So i can not calculate a U-factor of the frame for the whole green hatch (see page 2).

 

How should i change this detail to get the correct U-Factor of the frame for the exterior part (green hatch page 2)?

 

In addition the drawing shows an corner detail. How should i handle this situation?

 

I think that THERM is calculating the u-factor just in one heat flux direction (see page 3). If i calculate an U-factor of the frame in x direction, just the area of the projected surface of the "U-factor surface frame" will be considered at the outer surface.

My opinion is, that the heat flux is going in x and y direction in this corner (see page 4)

 

Could you give me please some advice to solve this issue?

Christian

[Fabrizio Prato]

Hi Christian.

Your question is rather thorny; I try to answer even if I'm not quite sure to understand your issue.

If U values of your curtain wall unit (frame, opaque and transparent panels), are what you're looking for then I think you should refer to EN ISO 10077-2 and EN ISO 12631 (that replaced EN ISO 13947). In this case I would only model the curtain wall unit WITHOUT any other part of the building as shown on the left side of the attached image.

If instead Psi values of superior and inferior corners of your installed curtain wall unit are what you're looking for then I think you should refer to EN ISO 10211 and accordingly model both curtain wall unit AND building structures as shown in the right side of the image.

Sorry, but these are the only things I can suggest to you.

Fabrizio

[Christian Rehner]

Hi Farbrizio and other Therm-users,

thank you for your answer!

I have to calculate with DIN EN ISO 10077-1, -2 and DIN EN 12 631 to get an NFRC100 certified u-value.

So i have to calculate my glass, opaque and edge-u-values.

I just added my therm file "Corner Detail Down" to show in which way i calculated it now:

I get an u-value of 0,8677 W/m²K at a length of 128,841mm. I added at the adiabatic boundary condition type the "u-factor-surface" to "frame" to get this result.

Do you think this is correct now?

Furthermore i added an other therm-file "Corner Detail Top" with an similar issue at an Corner detail.

When i splitted the Detail, because there is a vertical and horizontal section, i mentioned that the edge values differ from 5,2599 W/m²K to 2,4396 W/m²K

I think the reason is, because the projected direction of the heat-flux was first the double size because of the edge of the vertical and horizontal section.

So i calculated the u-factor surface just to the middle of the Aluminium Profile ( see in "Corner Detail Up section up 20° tilt")

Should i also use the adiabatic boundary conditions in this case as frame-"u-factor-surface" to get the right amount of the heat-flux?

Do you think this is the right strategy?

Christian

[Fabrizio Prato]

Hi again Christian.

Form what I can see now of your drawings and from what you write in your post the curtain wall module should be that on the left of the first attacched image where I have highlighted all the nodes and panels of which U values have to be calculated to determine the average U value of the curtain wall module accordingly to EN ISO 12631.

On the right side of the second and third attached images I then highlighted all the nodes that should be modeled in Therm to calculate each Uf value according to EN ISO 10077-2, (section planes with z axis are simbolized by the orange rectangles)

U value of opaque and transparent panel are calculated using EN ISO 6946 if possible, otherwise using Therm and Windows calculations or obtained by laboratory tests made accordingly the EN ISO standards for these objects (I don't remember their numbers)

Finally, with all these U values of frame profiles, U values of opaque and transparent panels and their installation Psi_g values, the average U value of your curtain wall module can be determined, accordingly to EN ISO 12631.

This is what I can say on the subject.
But I think a specialized laboratory should be consulted.

Ciao
Fabrizio

[Christian Rehner]

Hi again,

i know which sections i need to calculate for my overall u-value. This was not my question.

The question was how i can calculate a right u-value for the frame (marked u-frame in the first pdf) at a corner detail with Therm in aspects regarding the geometrical heat flux at the corner detail.

Christian