AW: [TRNSYS-users] Problem with Uwin value and Uframe

["Matthias Rudolph" <rudolph@transsolar.com>]

Dear Amelie and Diego,

another effect that has to be taken into accout is that the u-value of the window depends on the temperature difference
between the panes. At low temperature differences the u-value decreases.

kind regards,
Matthias

-----Ursprüngliche Nachricht-----
Von: trnsys-users-bounces@engr.wisc.edu [mailto:trnsys-users-bounces@engr.wisc.edu] Im Auftrag von Diego A. Arias
Gesendet: Donnerstag, 1. September 2005 23:42
An: trnsys-users@engr.wisc.edu
Betreff: Re: [TRNSYS-users] Problem with Uwin value and Uframe


Dear Amelie:

I think I have an idea of what is happening.  I would recommend looking 
at section 2.2.8. of the second part of Volume 
'6-MultizoneBuilding.pdf'.  Paraphrasing what this section explains:
- u_window = f_frame * u_frame + (1 - f_frame) * u_glass
- u_glass = (A_centr * u_centr + A_edge*u_edge) / (A_cent + A_edge)
- u_edge = c_edge,1 + c_edge,2* u_centr + c_edge,3 * u_centr2 where, u_window : u-value of the window, taking into account edge effects and 
frame effects.
u_glass: u-value of the window, taking into account the edge effects.
u_edge: u-value of the glazing edge of the glass.  This value is 
calculated by the program WINDOW4.1, and in implemented in the window 
library.
u_centr: center of glass u-value

Therefore, the value that you get, 2.1 W/(m².K), does not take into 
account the edge effects that Prebid is calculating.  I hope this 
helps.  Please let me know if you have additional questions.

Diego

> We have a problem about the U-value of the windows described
> in Prebid. The value given by TRNSYS simulation does not match with 
> the one we calculate ourselves.
>
> For example, on a very basic building with only one window and no
> solar radiation at all, when Ug=1.3 W/(m².K), Uf=23.88 kJ/(h.m².K) and 
> area of frame per window x=0.15, we calculate Uw=Ug*(1-x)+Uf/3.6*x=2.1 
> W/(m².K), and the u-win value output by Prebid is 1.81 W/(m².K).
>
> Is there an explanation to these results and how can we be sure to
> give Prebid the right value of Uframe in ordert to get the right value 
> of u-win (here (2.1 w/(m².K) )?
>

-- 

Diego A. Arias
TRNSYS Coordinator
Solar Energy Laboratory
University of Wisconsin - Madison
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