Heat Dissipation for Controls Enclosure 2

[robbm]

I have a formula that was given me for determining the required surface area of an enclosure, but I'm curious if anyone else has seen it or knows where I might be able to find it. I want to make sure I can show a legitimate source for it should anyone request more info on my calculations. Obvisouly, this formula requires you to know the heat load of the panel (in watts) and the amount of allowable increase in temperature (in °C). Here it is, any help would be great...

(watts to dissipate) x 300
--------------------------- = required surface area
?T in °C


thanks again.

 

[Mobius44]

Your equation leaves out the answer's units of measure(in^2, cm^2, etc).

There are several other factor's that your equation must be including assumptions for, like panel material (steel, aluminum, fiberglass) and whether it's inside or oustide (solar loading).

I suggest using thermal management equations from panel box mfg.'s, for instance Hoffman page A.36 and A.37 of spec guide volume 20.

-Sean

 

[robbm]

oops, sorry. the units of measure are in^2. and our panel material is stainless steel and all enclosures are located indoors. the main thing i dont particularly like about the hoffman guide is that you have to rely on a graph for estimating the temperature rise. also, we tend to size our box and loads and then will find out our temperature 'tolerance' so estimating the temperature difference from the graph is somewhat backwards to the way we calculate things. you aren't familiar with this formula though? the person we got it through received it from an Allen Bradley drives specialist and we're trying to find out more info on it.

 

[djs]

Hello;
Hoffman has downloadable software that performs your calculation. follow this link:

http://www.hoffmanonline.com/produc...?cat_1=34&cat_2=375&SelectCatID=375&CatId=375

 

[LionelHutz]

I have seen numbers like that. We've used 0.6W per square foot of surface area gives 1C rise which is just a different factor than your formula (0.48W). Is it correct - not really due to things such as sun loading and the heat rising to the top of the box but it will work OK in many cases.

 

[itsmoked]

robbm; Please note this thread on exactly your subject.
thread248-158079

I cannot see how your equation even comes close to describing the true situation. This is from years of experience with jamming stuff into metal enclosures.

If the shape of the box is not considered then the result will be utterly worthless.

Remember that only the top surface and a rapidly decaying down-the-sides gradient area are able to dissipate any of the heat from inside a sealed enclosure. Because of the truly pure convection system present inside the box the warmer less dense air all sprints for the top and then just statically sits there - stratified down from the top.

And if sunlight hits the box directly it's toast!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com