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Which variable is more appropriate for shading control?

asked 2023-08-03 17:10:03 -0500

Selma Inger's avatar

Dear unmethours members.

I am studying shaiding (venetian blind) control. During selection of input variables shading control, I found two varaibles which express solar beam's incidence.

The one is "Surface Outside Face Beam Solar Incident Angle Cosine Value". This variable indirectly expresses solar incident angle. But EnergyPlus example employs this variable for solar blocking, which is about shading control by EMS.

Another is "Surface Window Solar Horizontal Profile Angle". This directly expresses solar incident profile by projection of solar beam vector on wall. It is said that in EnergyPlus document."For a vertical exterior window, this is an angle appropriate for calculating beam solar quantities appropriate to horizontal window elements such as horizontal reveal surfaces, horizontal frame and divider elements and horizontal slats of window blinds. It is defined as the angle between the window outward normal and the projection of the sun’s ray on the vertical plane containing the outward normal." From the document, it is described for this variable to be more proper to shading control, especially Venetian blind.

However, I think that "Surface Window Solar Horizontal Profile Anlge" is hard to calculate in reality. Also, I want to know the big difference between first one that is translated to degree, and second one. In my thought, solar incident angle (translated from cosine to degree) expresses solar position in detail regarding specific surface.

image description

(I've attached an image)

In this image, during solar beam inciding to south wall (not tilted), it is not that much different. I hope the positivie reponses that which variable is more practically appropriate to blind slat angle control.

Sincerely, thank you.

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2 Answers

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answered 2023-08-05 10:42:58 -0500

updated 2023-08-05 10:43:56 -0500

I use these two variables (my shading control is “OnIfHighSolarOnWindows”)

Surface Outside Face Incident Solar radiation Rate per Area (W/m2)

Surface Window System Solar Transmitance (--)

But probably in some cases if you use other shading control other variables can also be helpful

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answered 2023-08-09 18:56:32 -0500

Rebecca Powles's avatar

The profile angle is the angle the direct solar radiation makes with a horizontal line in a vertical plane that is perpendicular to the surface. The other angle is the angle the direct solar radiation makes with the normal to the surface.

For controlling venetian blinds with horizontal slats, the profile angle is appropriate. For vertical blinds, or other shades which have properties depending on both the profile and azimuthal angle, the profile angle is less appropriate.

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Asked: 2023-08-03 17:10:03 -0500

Seen: 121 times

Last updated: Aug 09 '23