IES-VE User Forum

Dear all!

Could someone help me with the difference between external and internal incident solar flux at surface variables in VISTA.

The external incident solar flux is the sum of direct and diffuse solar radiation. That is easy.
But what is the internal incident solar flux? I thought, it is the rest of the external incident solar flux after the transmission through the transparent window material. However, the values are small for it.
Such as: Ext. surface incident solar flux is 335 W/m², the int. surface incident solar flux is 10 W/m².
My window had only one layer. g-value = 0.90. No internal or external shading system installed.
You see, the factor between the values in front of the window and behind the window is round about 33.5. I wonder why! Is there something I forget or complete misunderstood?

THX.

Hi!

Has anyone an idea?
I keep on searching for a solution.

Thank you.

Hi,

The Vista user guide defines it as:

Incident solar flux: The solar flux (irradiance) incident on the surface.

My understanding is that internal solar flux simply refers to the internal side of the surface (e.g the bit you might put wall paper on).

And external solar flux refers to the outside surface (e.g. the bit you might put render on).

Hence the internal flux is very small eg. 10 W/m2

Im not 100% sure this is correct, but 15 minutes playing around with a room with and without rooflights should confirm things.

Ross

Hi there!

Good idea, but I think we misunderstand each other ...

So you think that the internal solar irradiation is the diffuse reflection of the other internal surfaces? That could be very possible. ...
It helps me but unfortunately not. To check the function of the window structure I am looking for the value behind the window pane. Is it possible to calculate this value?
In Vista, the variable of the solar gain is the entry on all internal surfaces (This is so in the manual.). I'm confused.

Thank you.

Greetings ZWP Inno

Hi,

I have possibly misunderstood. Its hard to describe the situation on a forum.

Can you post up a picture of the room you are trying to look at?

I think the internal solar flux may only account for the radiation from inside the room hitting the window.
Hence anything passing through it will no be counted.

In which case the ratio of external to internal will in no way resemble your G-value.

I hope this helps

Ross

Hi,

I do think Ross is right here, the internal is what has come into the space already and then hits the inside of the surface you are looking at, it's not the inner pane of a double glazed window say. I don't think Vista can tell you that, perhaps it can be calculated manually from the incident external solar value reported and your own knowledge of the properties of the glazing unit?

Phil

Hi!
Of course I can count it manually. But I wanted cleared out whether the model correctly anticipates the window. That does not seem to be possible, that's too bad.
For the evaluation, I could have used it very well. Especially for the presentation of results.
Thank you.