[TRNSYS-users] about Uw, Ug, g of window in Trnbuild

Mon Jul 25 03:03:11 PDT 2011

Dear all

Following the questioning here below I must admit that window
characteristics specifications are not clear to me at the moment.

What I usually have when I start modeling a building project is the Uw
(whole window heat transmission factor), Ug (glazing), Sg (glazing solar
factor) and CLR (clear ratio = glazing area / total area) values.

What I usually don’t have is the Uf (frame) value and the time to model the
window with WINDOW software.

So here is the process I came down to.

1/ I chose the most similar window in TRNSYS window lib.

2/ I get the Ug value shown in TRNBUILD.

First question: Is this the U value for the glazing only as the data file
includes frame definition?

Second question: The corresponding value in the data file is obtained at
different ambient conditions (26.7°C e.g.) than the ones specified in the
Norm (-18°C e.g.). Why is it so?

3/ I calculate the Uf value to aim at the desired Uw value.

Third question: In TRNBUILD I must specify a “raw” value without convective
and radiative contributions which are processed separately by TRNSYS.
However the convective coefficients are said to be applied on both the frame
and the glazing together which collides with the individual approach used in
the Norm. To comply with what seems to be done by TRNSYS I thus use the
following formula:

Uf = [ 1 / (1/Uw - Rse - Rsi) – CLR*1 / (1/Ug - Rse - Rsi) ] / (1 - CLR)
where Rse, Rsi are the whole surface resistances Rs = 1/ (hconv+hrad).

Q°: Is it correct to consider the same Rs values for Uw and Ug (as it will
be done eventually by TRNSYS anyway for the convective part)? 

4/ I assess the solar factor difference between my “artificial window” and
the reference value I have and specify it as an external shade factor in
TRNBUILD.

Here I use the Norm formula which is a little bit complicated so I will
spare you the trouble.

5/ I eventually check the results of this rather intricate process with an
elementary simulation test case.

I use TRNSYS QUA variable with a few basic corrections and I typically get a
value of Uw = 2.17 W/m2.K for a reference value of 2.1 which I consider
satisfactory.

Q°: Is there a way to get directly the Uw value calculated by TRNBUILD?

Thank you very much for any answer you might have.

Best

--

Antoine Gautier
Solamen
+33 6 98 78 56 46

antoine.gautier at solamen.fr

Yujun TAO
<mailto:trnsys-users%40cae.wisc.edu?Subject=%5BTRNSYS-users%5D%20about%20Uw%
2C%20Ug%2C%20g%20of%20window%20in%20Trnbuild&In-Reply-To=> aleck1314 at
yahoo.fr 
Thu Oct 22 06:34:50 CDT 2009

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  _____  

hello users,
I detected something strange about Window in Trnbuild. Or maybe I don't
really understand.

I find the calculation of Uw (U-value of the window), Ug (U-value of
glazing) in Trnbuild is very scientific like they depend the outdoor
temperature, the wind and the insolation. 

But these values are not clearly showed in Trnbuild, because I found the
value (U-value of glazing) showed in the "window" was taken frow the files
"W4-lib" or "Prgwin" in following location (outdoor temperature=26.7°C°,
Solar (W/m².K)=0, WdSpd(m/s)=6.71, hcout, hrout,  hin = (respectively)
25.47,  3.18,  6.89).
You can find in the attached document with the location I indicated. 

It's not taken from the description location at the bottom of W4-lib or
Prgwin files, neither from the head of Prgwin file.
So I want to know curiously in the condition of european norm (CEN), how you
defined a window and checked it (Ug, Uw) that you expected. Or more far in
every different norm.

Because the U-value in these descriptions is Uw (total window) said in the
tutorial of window5, 
So for me, this value isn't useful because we can change the frame in the
dialogue of"window". It's only useful for me when it's Ug and showed in the
glazing in the dialogue of "window"(Trnbuild). I don't know if the TRNSYS 17
can do it.

Second question is about g-value,
I don't know where is g-value from, because the two values (middle of
description of one window, bottom of W4-lib, Prgwin files) are the same. If
it's like U-value said in the tutorial of window5, so it's should be used
for total window, not for glazing.

After all, for me, the indication of U-value, g-value of window in Trnbuild
of TRNSYS 16 is strange and not according to the Norm (International, etc.),
I want to know your experiences.

Aleck

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