Re: [EnergyPlus_Support] Re: Solar distribution in a double skin facade against simple skin results

[ppeixeiro@xxxxxxx]

Your interior window is defined two times: once in each zone they
seperate. It might be the case that you're reporting "Beam Solar
transmitted through interior window" for the inteiror window on the
surface of the DSF zone, and it should be the window that is located the
surface of the main zone.


> Pedro,
>
> In regards with the transmission of solar energy through the double skin,
> I have a question:
>
> In the results, we can see that the output variables at the building
> central zone level (the zone supposedly protected by the DS system)are
> generated, say you have about 20kW of Zone beam solar from interior
> windows and 40kW of Zone diffuse solar from interior windows.
> It is weird that I have a 0 value for the interior window level ouput
> "Beam Solar transmitted through interior window" I don't quite understand
> that...
> Because of that I am not sure anymore how E+ handles the solar in and out
> the zone and the cavity.
> I am not sure if the big difference I was talking about in my first
> message was not due to the fact that only the diffuse part is well treated
> here...What do you think?
> Because the impact of the cavity airflow is clearly on the glazing net
> gains which makes sense since it cools down the structure that was partly
> charged with solar heat, hence one can say it takes away part of the sun
> heat (although I still think it is small).
>
> Aymeric
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Pedro Peixeiro <ppeixeiro@...>
> wrote:
>>
>> 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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