[TRNSYS-users] U-value glazing

[bdo@stb.rwth-aachen.de]

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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