Specs for sunlight exposure on outdoor elec equipment.

• Apr 13, 2003

• #2

cubic

Military

Mar 11, 2003

1

CN

you should also consider the absorbtion effect

 

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• Apr 21, 2003

• #3

cbiber

Mechanical

Apr 18, 2003

49

US

The spec may be an oversimplification, or specific to a certain geography... and did it say what to use for the insolation (incoming radiation)?

I'd use some geometry and let the spreadsheet figure it out for me. What can I say, I'm lazy!

Biber Thermal Design

http://www.biberthermal.com

 

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• Apr 21, 2003

• Thread starter
• #4

Tunalover

Mechanical

Mar 28, 2002

1,179

US

Folks-
I'm one of those overly-practical design engineers who would rather impose a spec than do the calculations for a particular case (besides, the equipment may be placed ANYWHERE by the customer). The solar radiation, call it "S" (W/m^2) I can obtain for various regions of the world at the hottest time of day. I was really looking for the spec number that helps apportion the incoming radiation to the sides and top for general design purposes.

Before I can figure the absorbed heat (Qa=alpha*S*A) I first need to nail down the apportioning to the sides and top.

Thanks,
Tunalover

 

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• Apr 21, 2003

• #5

IRstuff

Aerospace

Jun 3, 2002

44,911

US

The basic value for solar load is about 1152 W/m^2. If you track down an architectural lighting program, it should be able to provide with the sun slant angle as a function of time of year and you can couple that with what you might expect the ground to be at any given installation.

Otherwise, you'll just have to assume the maximu solar load directly impinging plus a 20% diffuse reflective ground cover.

TTFN

 

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• Jun 2, 2003

• #6

smltwnboy

Mechanical

Feb 17, 2003

4

US

I would look at Mil-Std-810...There's a wealth of information in there, solar exposure is just one of the topics (section 505.4). Perhaps you can extract what you need.

 

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• Jun 2, 2003

• #7

cbiber

Mechanical

Apr 18, 2003

49

US

Check out a similar thread in the Heat Transfer & Thermo forum. (Sorry, I don't know how to put in the link!) It's called "Solar Radiation on an Object".

 

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• Jun 4, 2003

• Thread starter
• #8

Tunalover

Mechanical

Mar 28, 2002

1,179

US

smltwnboy-Thanks but it does not provide the apportioning of the sun to the top, sides, bottom.

cbiber-Thanks. I looked it up but ended up providing more information than I gained.

This is what I have recently found:
The fraction of exposure to the top and sides is available from BELLCORE TR-NWT-000057 Functional Criteria for Digital Loop Carrier Systems. For lack of better data, the fraction of exposure to the bottom I will assume to be .1 to make provision for scattered and reflected environmental radiation. Otherwise, per the spec the top sees 1.0 and the sides and ends see .50. Of course if the object is sitting on the ground, the bottom will have only conduction cooling to whatever it rests on. Mil-Std 810F says to use 1120W/sqm for enclosures with short time constants (2hrs or less) residing in the hottest places on earth.

 

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