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Dear Knut, dear Joke A g-value is always
defined for a shading device in combination with a glazing. As the g-value
includes the heat flow from the internal surface (glazing) to the room, a
definition of a g-value of a shading device without a glazing does not make sense.
In TRNSYS the shading
device is modeled by the external shading factor, which reduces the solar
radiation on the window. The heat flow to the room is reduced by the same
factor. So in my opinion Joke’s calculation is correct: external shading factor =
1 – (gwindow+shadingdevice / gwindow) Best regards Nikolai Nikolai Artmann 3-Plan Haustechnik AG, Winterthur Von: Knut Erik
Enerstvedt [mailto:knut.erik.enerstvedt@gmail.com] Joke, I think you should
only consider the g-value of the shading device when calculating external
shading factor. The g-value of the window is
handled separately. So if the g-value of your shading device is 0.23, the
external shading factor becomes 1 -
0.23 = 0.77. Someone please
correct me if I am wrong. Kind regards, Knut Erik
Enerstvedt >Dear
trnsys-users, >I’ve
a question about how to calculate the external shading factor (multizone
building). Is the following correct? >Suppose
I’ve a window with a g-value of 0,37 and a g-value of 0,23 (external
shading device + window). >The
external shading factor becomes then: 1 – (gwindow+shadingdevice/
gwindow) = 1- (0.23/0.37) = 0.38 >Kind
regards, >Joke De Beuckelaer >project engineer mep |