Re: [TRNSYS-users] U-value glazing

["hotline" <hotline@transsolar.com>]

Bernd,
the u-value referred to in the manual is for display in TRNBuild only (we will change the manual in order to make it clearer).
The u-value of the window is calculated for each timestep depending on the pane temperatures. This u-value is even used in the balances. 

Kind regards
Monika
TRANSSOLAR Software Team




> -----Ursprüngliche Nachricht-----
> Von: bdo@stb.rwth-aachen.de [mailto:bdo@stb.rwth-aachen.de] 
> Gesendet: Montag, 11. Juni 2007 18:40
> An: trnsys-users@engr.wisc.edu
> Cc: thomas@stb.rwth-aachen.de
> Betreff: [TRNSYS-users] U-value glazing
> 
> 
> I have a question regarding the thermal properties of 
> external windows. 
> According to the documentation (6-127) "...the Ug-value at 26.7°C, no 
> solar radiation and 6.71 m/s windspeed are read and used by 
> Type 56 for 
> the calculation of the thermal and optical window behavior". The edge 
> correction is done by calculating the U-value for the glazing 
> edge. Uedge = cedge,1 + cedge,2 ucentr + cedge,3 u²centr Eq. 
> 6.3.2-94 I did this calculation for window 2001 from the 
> w4-lib and set the 
> fraction of the frame = 0 for easier control of the results. Having a 
> fixed room temperature of 20°C and no insolation, TRNSYS 16 
> produced the 
> following outputs:
> for TA=0°C U=1,66 W/m²K
> for TA=15,6°C U=1,54
> for TA=26,7°C U=1,58
> for TA=37,8°C U=1,62
> 
> Doing a calculation of my own with Eq. 6.3.2-94 and using 
> Glass Height: 
> 1079.5 mm,Glass Width 774.7 mm, my result has been 1,72 W/m²K. When 
> using the data from TA=15,6, and 36,7°C, no insolation, and a 
> windspeed 
> of 6,71m/s my results were U=1,68 and U=1,83W/m².
> Why are the TRNSYS outputs fluctuating with the temperature? How are 
> they calculated? Are the output values used for the thermal 
> balance of 
> the zone, too (besides a slightly different surface resistance)?
> 
> With best regards,
> 
> Bernd.
> 
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