Switchboard Internal Temperature 1

[stanier]

I am looking at a project where the customer is arguing about what colour to paint the exterior surface of the swithboards. The local residents want dark green and we are trying to justify this as far as internal temeprature is concerned. the swithboard consists of an internal IP45 cubicle with vents top and bottom housed in a kiosk that again has vents top and bottom (gives chimney effect). Solar radiation and ambient temperatures of 50C are a problem in Australia.

Has anyone any software, technical articles etc for this exercise?

 

[IRstuff]

EOI has a table of emissivities:

http://www.electro-optical.com/bb_rad/emissivity/matlemisivty.htm

Hope that helps.

TTFN

 

[richvangenr1]

There are IR reflective pigments that can be used as a primer to reduce the surface temperatures. You may want to contact Ferro in Washington PA who authored an
article “When Black is White” on the Paint and Coatings Industry web site:

http://www.pcimag.com/CDA/ArticleInformation/coverstory/BNPCoverStoryItem/0,1848,17187,00.html

Hope this helps.

 

[JKEngineer]

Let me be a bit of a contrarian here. It sounds like we are all assuming that the best coating for the outside is a reflective one. (I sort of think so too, but read on.)

I am not that familiar with switchgear, and even less so with Australian nomenclature for same, but it sounds like you have a heat producing element in a vented box that is inside an outer vented box. The rest of my comments are based on this.

Consider: it is said that the Bedouins who wear black clothes are actually cooler than those wearing white because the hot clothes create an enhanced chimney effect.

Also consider: in addition to the solar heat loads in question, there is the internal heat load of the power equipment. If this is significant, then a high emissivity coating may be more desirable for increasing the heat rejection of the internal heat, than a reflective coating's rejection of solar load.

An FEA or CFD model, including the transients of solar load and the chimney configuration would be an appropriate way to look at this problem.

Of course if the internal heat load is very low then its rejection becomes unimportant. The chimney effect is still in question however. (and why put that type of structure in if the internal is very low)

richvanger1 suggests a primer to reduce emissivty. It is my understanding that a primer would not be effective if there is another coating over it. The top coat's properties would govern.

If it proves that low e is good, then you might still use dark green with aluminum flake dispersed in it, or another low e approach. (Just watch out for the glare! ;-))

I have done some models along these lines in FEA. They can be quite informative. Some samples are on my website, if you are interested. Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[JOM]

JK,

This is a bit off-topic (well, completely off-topic), but..

Is thermography applicable to identifying below zero C temperatures? That is, where the abnormal temperatures are cold rather than hot.

JOM. Cheers,
John.

 

[JKEngineer]

John -
The off topic answer is "absolutely" (no pun intended -- in fact you will have to look real hard to find it! ;-) )

Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[JOM]

JK,

Can't spot the pun
Cheers,
John.

 

[JKEngineer]

Oh well.
"Absolutely" (zero), as in very, very cold.

Stop groaning after 5 minutes. Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[JOM]

JK, that's pathetic.

This came to me in traffic:

absolutely>absolute temperature scale>degrees Kelvin>Calvin Klein>Jack Kleinfeld (you)

Now that's a pun!
Cheers,
John.

 

[JKEngineer]

Stanier -

I just came across a discussion in places that shall remain nameless (being red flagged by the owner is the worst ;-) ) but I pass on some thought from it.

It related to a similar situation. The points made were:
(appropriate)white paint has low absorptivity in the wavebands in which most of the solar radiation's energy is concentrated, i.e., visible light.
just about any paint has high emissivity in the IR at wavelengths that correspond to peak energy emissions for ambient to warm ambient temperatures.

This leads to the suggestion of white exterior to reduce solar loading while maximizing re-radiation of the heat from the components. The heat generation of the components becomes a very important consideration in this, especially when the discussion moves, as this one did, to the correct paint color or metal coating for the INSIDE of the box. If the components are going to generate enough heat to be hotter than the shell, then the inside paint should be absorptive to allow the components to radiate to it and then have the shell send it outwards. If the components are going to be cooler than the shell, then the interior should be reflective. This will reduce the loading from the shell to the component.

The process of using the white paint as reflective in the visible and emittive in the IR is called Selective Coating.

Hope this helps. Still sounds like a dark exterior, if you have solar exposure is probably a bad idea under normal circumstances. (My contrarian opinions above not withstanding.) Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com