External Shading Device Transmittance Factor

[SakuraOno]

Hello,

I have 2 questions regarding the Transmittance Factor input fields under the External Shading Device dialogue.

1) for the degree, does 0 degree mean completely parallel to ground? or does it mean completely parallel to the glazing?

2) Also, I don't understand completely why we have to do this in 15 degree increment?

Is this because there's no other way of specifying the geometry of the shading device (because unlike Local Shading, External Shading Device doesn't allow you to specify width, offsets, etc, basically the shape of the device?

So does this mean that in order to figure out what I should put for the transmittance at various degrees, I just have to do some quick drawing/calculations to figure it out? sorry if this is a dumb question, but I just want to make sure I understand this correctly.

Thanks!

[PCully]

Hi,

1. From the user guide

The angle in question is the solar altitude measured in a vertical plane perpendicular to the glazing construction.

I take this to mean 0 is suns rays parallel to the ground so in general you'd have a larger transmission at 0 and typical shading devices would be closer to 0 as you approach 90 degrees.

A test sim measuring solar gain with and without the shading device defined would let you see the effects of this by comparing early morning versus midday when solar altitude peaks.

2. This is to permit slatted shading devices to be represented where the transmittance will vary with the solar altitude, if you are modelling something that will not vary then you can enter the same value here for all inputs so it is consistent.

Phil