Hi Aymeric
SHGC is the amount of solar radiation that enters a room both directly transmitted through the facade and the fraction of radiation that its absorbed by the facade and then transmitted into the room by both convection and radiation heat transfer. In the pressence of a DSF, there is a certain amount of heat transfer occurring inside the cavity (heat removed by the air flow). This amount is not stationary, because it depends on wind incidence, wind velocity, temperature difference between cavity air and outside air, and surface temperature of the panes. Because of this un-steady state heat flow, its not possible to establish a convectional SHGC value for a DSF. Also, in reality, the heat flow also varies with the height of cavity (temperature inside the cavity increases with height) and so will heat transfer through the inside pane. So it basically means we would get a difference SHGC value in function of height, which complicates even more a definition of a single SHGC value for a facade.
Pedro
On 01-04-2011 11:43, aymericnovel wrote:
Dear all,
I am studying a double skin facade design. I want to compare with a design using a simple skin with windows that have a SHGC of 0.25 because it is the assembly SHGC I have to reach according to the local chinese standard. See the architect have asked me to justify the cost of using the external skin...good question when you think about it!
So I have chosen inner skin and outer skin glazings so that it is equivalent first with a simple approximation of SHGCin x SHGCout = 0.25 . I know it is too simple but still it should not be too different in the zone inside the building.
I am having trouble understanding the following fact:
Having a combined SHGC of the inner and outer skin very close to the simple skin I try to compare with, I do not obtain at all the same amount of sun in the zone inside the building. Why? Normally the sum of the direct and diffuse solar transmitted through the internal windows should be close to the one through the external window in the case of the simple skin no?
I have the feeling I am totally missing something basic here but it's late and I don't see it.
Your help is more than appreciated!
Thanks
Aymeric
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