Edge effects windows.

["Jong, M.J.M." <jong@xxxxxx>]

Dear TRNSYS users,

At the moment I am simulating an old office building. The office building is
provided with a lot of windows with frames seperated by dividers (in one
frame, there are many little windows). At the moment, the building is
provided with single pane glazing. To reduce the amount of energy for room
heating, a possibility is to provide the windows with double glazing. A
disadvantage of a window with a frame that is provided with dividers is that
the edge effect of the glazing has a great influence on the total U value of
the window. I tried to simulate this effect in TRNSYS 15.3.

First I made a simple 4 zones box model. The dimensions of every zone are 2
x 2 x 2  m. In one external wall in every zone there is a window of 1 m2,
with 21.6 % frame area. The total annual heating demand of this box is 5.21
GJ/year.

For the second simulation, I modified the model to a model with in every
external wall 4 windows of 0.25 m2. In the first model I had an external
wall of 4 m2 with 1 m2 window in it. In the second model, I have 4 externall
walls of 0.5 m2 each with a window of 0.25 m2 in each wall. The frame area
is again 21.6 %. I defined both windows myself with the help of Window 4.1.
In window 4.1 I chose for a custom size and for the window in my first
simulation I had the dimensions of 1000 x 1000 mm (width of frame is 57.15
mm). The dimensions of the window in my second simulation were 500 x 500 mm
(width of the frame is 28.575 mm). The frame area of 4 windows of 500 x 500
mm is exactly the same as the frame area of a window of 1000 x 1000 mm. In
both simulation I chose in the windows menu for ID-spacer option 0 (data
from W4lib.dat). Also in this case the total annual heating demand was 5.21
GJ/year. To be exact, the difference in the annual heating demands was
0.00155 GJ/year. I think this is impossible. The heating demand of the model
with windows of 500 x 500 mm must be significant higher. Does anybody has
experience with the influence of the edge effects of windows on the heating
demand in TRNSYS ?  

Analysing the W4lib.dat file I found something that I do not understand. For
every window in the library, you can see values as shown below. As I
interpretate the numbers will, you have for 4 temperatures (-17.8, 15.6,
26.7 and 37.8 °C) the overall and the Center of Glass U-value of the window.
For every window in the library, these 2 U-values are exactly the same. I
think there must be a difference between these 2 U-values. The overall
U-value must be higher than the Centre of Glass value. Is this correct ?

Overall and Center of Glass Ig U-values (W/m2-C)
Outdoor Temperature                 -17.8 C      15.6 C      26.7 C
37.8 C
Solar      WdSpd  hcout hrout  hin
(W/m2)     (m/s)     (W/m2-C)
   0        0.00  12.25  3.24  7.59  1.44 1.44  1.35 1.35  1.38 1.38  1.45
1.45 
   0        6.71  25.47  3.21  7.62  1.51 1.51  1.39 1.39  1.43 1.43  1.51
1.51 
 783        0.00  12.25  3.41  6.82  1.41 1.41  1.42 1.42  1.47 1.47  1.53
1.53 
 783        6.71  25.47  3.31  7.10  1.51 1.51  1.45 1.45  1.51 1.51  1.56
1.56 

With kind regards,


Maurice Jong.

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Maurice Jong
ECN - Energy research Centre of the Netherlands		Department: DEGO
P.O. Box 1    1755 ZG  Petten				Country:   The
Netherlands
Telephone:    +31 (0)224 564938				Fax:       +31
(0)224 568966
E-mail: jong@ecn.nl					Internet:
http://www.ecn.nl/dego

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