external sunshade attched to window frame - how to model in THERM/WINDOW

[Raghu Pendyala]

Hi,  I have a sittuation that has a external horizontal sunshade is  in front of the window and attached to the mullions by way of alumimium brackets. See figure attached. There is heat flow between inside and outside, from the sunshade element,  through brackets, through jamb mullion. The question I have how to model the element in Therm 7.2 and assemble the model in Window 7.2.

Thank you.

Raghu Pendyala

[Jose Li]

We have encountered the same problem.

we do it this way: if the bracket part is not entire long, for example 100mm, First simulated the u value without the bracket. then with the bracket to calculated the thermal bridge effect like the screw example in the manual.

If the bracket part is as long as the head, then simulated u value with bracket.

But we are trying to find a better way.

[Dragan Vidanovic]

Hi,

This is not easy to do. In WINDOW 7 we have new type of shading device which we call BSDF (Bidirectional Scattering Distribution Function). It is function which will basically describe window optical properties for certain number of incoming directions. Standard for WINDOW is 145 incoming and 145 outgoing directions. If you install WINDOW 7.2 and go to C:\Users\Public\LBNL\WINDOW7.2\XML you will find some examples (woven shade mainly) for BSDF description. How to obtain BSDF for shading device is another story and in our case we are using Radiance ray tracing.

Simon

[D. Charlie Curcija/LBNL]

U-factor of a non-coplanar shade is only reflected through the potential thermal bridges for brackets, but those thermal bridges are point bridges (i.e., not continuous along the frame cross-section), so the rule is that they are not modeled (i.e., effect is small and is ignored). Much more important effect is reduction of solar transmittance and therefore SHGC and VT, but these effects cannot be modeled in THERM nor in WINDOW for non-coplanar shading systems. This capability is currently under development for THERM/WINDOW 8..

Charlie