PLC Panel Heat Load Analysis

Question

PLC Panel Heat Load Analysis

R_Roc (Electrical)

(OP)

24 Oct 16 17:40

I have designed a simple control panel that has an internal heat load of 199 Watts.
Its a 72x36x24 Hoffman Enclosure. This control panel is in a temperature controlled
building. None the less the specification is requiring me to do a heat load calculation
with an environment temp of 50°C. All parts in my panel I have verified at rated for
50°C.

The client states that the Outside and Inside Temp shall be 50°C for my calculation.
I tried to explain that a temp of 50°C outside an enclosure will never give the same temp at worst case
condition by using just a Fan. Just like a car. If a car outside temp is 50°C then inside temp will be at least 10° hotter, in
my case 55°C (132°F). By doing this I have now went over the parts rating. Any Suggestions how to describe/pass
my heat load calculations?

The only way to keep the panel at the same temperature at this worst case temp is to have a AC, which I don't need.
I'm I missing something? Any support will be greatly appreciated.

I'm using the Hoffman Cooling Analysis program for my Heat Load Calculation.

Thank you.

GroovyGuy (Electrical) · Answer 1 · 2016-10-25 00:19:30

Hi R-Roc,
I think to need to find a smarter 'client'. Any means to remove the heat from the cabinet, other than an AC unit, will always require a temperature differential.
200W of heat in such a large cabinet could almost certainly radiate the heat without the need for a fan. I suspect that the temperature differential will be only a few degrees C. Even with small fan (say 50cfm) the temperature differential will be much less.
Tell your 'client' that the exhaust temperature will be less than 1C higher than the inlet air temperature.
Regards,
CC

ps The Hoffman software package is very good, I have used it many times.

The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.
Winston Churchill

R_Roc (Electrical) · Answer 2 · 2016-10-26 16:26:45

I have met with the Client and informed me that I have now involved Hoffman Cooling/Thermal Engineer.
At very best we can put the outside temp to 122°F(50°C) and an inside temp of 125°F and the Hoffman
cooling analysis states we need a fan that can do about 400 CFM (overkill in my opinion), but
the client seemed to like this idea without having to provide an AC unit.

GroovyGuy (Electrical) · Answer 3 · 2016-10-27 01:43:19

Hey R-R,
That's 1 air change every 5s. Thtat otta suck the heat out.
Make sure you tie it down real good like; don't want it flying around the e-house. bat

GG

The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.
Winston Churchill

jraef (Electrical) · Answer 4 · 2016-12-01 17:03:52

Fans introduce contaminants, which can also increase your risk of failure in my opinion. I would evaluate the risk of that failure mode against the likelihood of the ambient ever getting out of control and rising to 50C. In a lot of cases, the ambient being that high may ultimately affect whatever else is going on in this space and require stopping that process, so making sure the control system functions might be a moot point.

If the client wants guaranteed operation at 50C ambient, he must accept that it can only be done reliably with active cooling. I have a project right now for a biotech firm who has a similar issue, PLUS they are not allowed to have anything with Freon in the area because even a small leak could result in major economic losses. So we have opted for Thermo Electric Cooling (TEC). This is a panel with a 40HP VFD in it, the TEC unit is costing me more than the VFD! They did not like the price tag, but it is what it is.

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

analogkid2digitalman (Electrical) · Answer 5 · 2016-12-01 18:20:28

Anyone ever use a compressed air based cooler (vortex tube) like these, just curious?

http://www.exair.com/en-US/Primary%20Navigation/Pr...

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
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itsmoked (Electrical) · Answer 6 · 2016-12-01 21:36:59

Let me fix that for you Jeff:

Quote:
it can only be done reliably with active cooling

'it can only be done unreliably with active cooling'

analogkid2digitalman; Yes it's done frequently but is fairly inefficient and can end up costing a lot when you add in maybe having to upsize the air-compressor and its annual electrical costs. They are dependable.

Keith Cress
kcress - http://www.flaminsystems.com

analogkid2digitalman (Electrical) · Answer 7 · 2016-12-01 21:45:23

Keith:

Good take on my handle! (A combo of two Rush song titles, not to mention my transition from hobby to career)

I figured they might be air hogs, not to mention added noise depending on cooling capacity required.

Thanks

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

GroovyGuy (Electrical) · Answer 8 · 2016-12-02 06:56:50

I agree with jraef in that a fan can suck dust and crap into your panel. Obviously if you must have a fan, there are a couple of things you should do, including;
- install filters on the air intake louvers on the panel ,and
- install a cooling-type t-stat on the fan and set it high enough that the fan only runs when the interior temperature is very high. [based on the info that you provided above, this would imply that the fan will never have to operate]

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

jraef (Electrical) · Answer 9 · 2016-12-02 07:15:58

I once investigated a proposal on using a vortex cooler for a control panel on an overhead crane over a pot line at an aluminum mill, i.e. very very hot. Conceptually I liked it because in addition to the cooling, the positive air pressure would keep contaminants out of the electronics.

The smallest vortex cooler required an amount of air that translated to a 7-1/2HP air compressor running continuously. It was a real eye opener.

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

itsmoked (Electrical) · Answer 10 · 2016-12-02 08:00:05

In lue of fans I've switched my customers to heat exchangers. They are the ones with two fans. One blows dirty outside air across the outside top end of the heatpipes and the other blows clean inside air across the inside bottom end of the heatpipes. No air exchanges with the inside of the enclosure at all. It's saved a lot of machinetools from coolant mist and ceramic dust.

There are primarily two types.

One has a horizontal flange and mounts thru the top of an enclosure. It works well because the hot air at the top inside efficiently drives the thermal transfer.

The other style mounts on the enclosure door or side having a vertical flange.

Keith Cress
kcress - http://www.flaminsystems.com

danw2 (Industrial) · Answer 11 · 2016-12-02 18:51:09

>The smallest vortex cooler required an amount of air that translated to a 7-1/2HP air compressor running continuously. It was a real eye opener.

Wow. Thanks for the reality check on the energy useage.

itsmoked (Electrical) · Answer 12 · 2016-12-02 21:56:42

Yep. It takes about 1Hp for every 4SCFM at 100psi (which is the pressure vortex coolers require). A typical vortex cooler can require 35SCFM.

Keith Cress
kcress - http://www.flaminsystems.com

jraef (Electrical) · Answer 13 · 2016-12-03 22:30:39

I like heat exchangers too, but they require at least a 10degC delta if I recall. Side note Keith, that technology was developed here in the Bay Area at a company that is now called Noten, origianally for the stantions used to hold the Trans-Alaska Pipeline off of the permafrost. They couldn't let the heat of the oil get to and melt the permafrost, but there was no power available to run anything active, had to be totally passive.

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

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