Something crazy going on with Ecotect reflectance values

[Anonymous]

Hi,

I have been doing some solar radiation simulations on a stadium which is covered in transparent plastic. I have modelled the platic as a window element. After playing around with various material properties related to solar radiation I have found a few things in Ecotect which are odd. I may be looking at this the wrong way but please steer me straight if you can see what I'm doing wrong.

I have done a whole lot of reading from various Ecotect sources. The one article which explained most of everything was this one though...

http://squ1.org/wiki/Solar_Absorption

From this article I withdrew several key ideas which are relevant to my particular model.

Firstly, the reflectance property is calculated based on the colour of the material. However, it is also possible to manually update the reflectance values.

Secondly, the following relationship is true: Absorption = 1 - Reflectance (Although I don't know where the transmission is represented in this)

Thirdly, SHGC is to solar radiation what the transparency is to light and both transparency and SHGC are completely interchangeable and cumulative.

Ecotect behaves very differently to what you might expect. I have tried altering the material properties on both version 5.5 & 5.6.

V5.5

After updating the reflectance values manually to 0.06, ecotect offered to update the absorption values for me. When I clicked yes the only thing I saw change was my SHGC. The SHGC updated to 1 - Transparency.

Now there's a couple of problems with this.
1. SHGC isn't the absorptance so why does it update?
2. Why does SHGC update to "1 - transparency"? If this is correct, the maximum overall transmission you can possibly have is 0.5(SHGC) x 0.5(Transparency) = 0.25(Overall transmission) because the SHGC and transparency are cumulative as I stated before.

Is the absorptance a background number which I cannot see? If so, then why do my results not change when I change the reflectivity without changing the SHGC?

V5.6

-In V5.6 this all changes. When altering the colour of a material it now changes the visible transmittance rather than the reflectance. As I said before the reflectance is based on the colour of the material...not the visible transmittance. So why does this happen?

Please help
Thanks
Tom Edited by: tomwilson1 on May 6, 2009 2:30 AM