Using fans to cool an Industrial Control Panel 10 - Eng-Tips

Hi,

I am trying to design an Industrial Control Panel that can be a drop-in replacement for an existing control panel that has been in service in a machine control application since the 's. The existing control panel (and the machine it controls) still works, but many of the the components inside it (PLC, drive boards, temperature controls, etc) are obsolete and unsupported. We are afraid that the failure of one of these components would result in significant downtime if we are not prepared. For this reason, we are hoping to do a pre-emptive upgrade of the entire control panel.

Using the original control panel for reference, I am trying to select modern (equivalent or hopefully better) components for each control function. While I am certain the original control panel would be found to be far from UL compliant if it were inspected, I am doing my best to choose components and follow practices defined in UL508A for the new control panel. (I am in the process of reading UL508A after receiving some great advice in response to another question I posted on this forum recently).

The question I have now come upon is this... The existing control panel has three solid-state relays that are used to regulate the power applied to resistance heaters. The new control panel will have similar solid state relays. These solid state relays generate some heat inside the panel. In the old control panel, there are two filtered ventilation openings on the lower part of the control panel (one on each side). (The filters look like a metal mesh). There is a fan mounted dead-center at the top of the old control panel that sucks air from above the panel and blows it down into the control panel. The intake side of this fan has the same type of filter as that used on the sides.

I was just wondering if anyone here can comment as to whether this sounds like a reasonable way to keep the inside of the panel as cool as possible (without resorting to air conditioning)? Before I "felt" the direction of air flow, it crossed my mind that there might be an advantage in having the fan on the top of the panel suck air from inside the panel and exhaust it above the panel.

Any comments will be greatly appreciated.

Thanks in advance,
Paul



Our old standard was to put cooling that pushed air into the cabinet either by a fan as you describe, or from a duct from a common cooling fan unit.
I still think there is no better solution.
Reason being, having in our case, one fan unit supplying cold air to many cabinets and over pressure makes it more energy efficient and it's less of a maintenance cost, then to have several small fan units and filters.
The installation cost is of course higher, but that is a one time cost.
Today usually they put in heat exchange units on each cabinet when needed.

The reason for for pushing air into the cabinet instead of sucking it out, is, regardless of which filters you use or how you try to isolate the cabinets you will always suck dust into the cabinet.

We have electrical cabinets that are over 35 years old which are supplied with incoming air which makes the cabinet "over pressurized" and they are almost as clean as they where 35 years ago.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein Not conclusively, but in my general experience the desired approach tis to have the "high pressure" zone inside the cabinet. The basic reasoning is that I want one of two things to occur: either I keep the "dirty environment" out of my cabinet, or I "exhaust" my dirty secrets out to the rest of the world, thereby keeping my cabinet clean(er). Is the OPs "blow down from top" approach truly optimal? In my opinion, no - it always works better to use physics to your advantage (hot air DOES rise!). Is it perhaps better because the parts that need the most cooling (or at least largest temperature differential) are located at the top of the cabinet? Maybe.

The trick to "clean" air flow is to have filtration on the air inlet (to capture the incoming "crud"), and some form of anti-varmint protection on the exhaust - usually louvres or screen, not actual filter - to minimize pressure drop through the whole system. For a "pressurized" system, that filter would normally be BEFORE the fan intake where it's easy to see, check, and change. For a "depressurize" system, the filters are at the actual air intakes (again easy to see, check, and change)which are going to be somewhere other than where the fan is located.

Converting energy to motion for more than half a century Dear Mr. PaulKraemer
#204A87]".......In the old control panel, there are two filtered ventilation openings on the lower part of the control panel (one on each side). (The filters look like a metal mesh). There is a fan mounted dead-center at the top of the old control panel that sucks air from above the panel and blows it down into the control panel. The intake side of this fan has the same type of filter as that used on the sides....."
I am of the opinion that:
1. assuming that there is NO over-temperature/heating problem with the old control panel and that new components do not generate more heat; the existing cooling air-flow volume is in order. But, see 2 below.
1.1 If you are considering to re-arrange the new components, try to locate those (heat generating parts) at the [bottom]. NOT at the top .
2. you mentioned that "....a fan mounted dead-center at the top of the old control panel that sucks air from above the panel and blows it down into the control panel. ....".
This is unusual to me. Usually, the top fan sucks in the (cool air) from/through the bottom two sides and blows/discharges the (hot air) through the top. Reason: hot air rises. No reason to blow (hot air) down to be discharged to outside, at the bottom!
3. Strongly recommend to reverse the top fan direction of rotation to blow/discharge instead of suction.
3.1. Refer the fan manual on how to reveres the rotation by electrical connection or reverse the fan installation, if possible?. Do NOT pull out the fan blade from the shaft and flit it over.
Che Kuan Yau (Singapore) All cabinets I have seen have the fan at the top, or more correctly at the side at the top and the outlet at the bottom.
The only reason I can think of for this is that the air is much cleaner at the top then at floor level where all the dirt sooner or later ends up, and having the fan at the bottom can also create a under pressure socking in air from the cable entries if it is at the bottom, which is common, in old cabinets they are not always so tightly sealed either.

Most electrical components at least here can stand at least +55 C, so pushing hot air down and out at floor level is usually sufficient to keep the components cool it is after all the amount of air exchange and the temperature on the incoming air that makes the biggest difference not which way the air goes.





“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein You are correct in what you say Che, I was merely pondering over why old cabinets where never built like that.

Still pondering.... even with filters on the fan, more dust will be pulled in when you open the door if the fan is at the bottom.
And for the function these old cabinets with the "wrong" airflow direction have, they still have done the job at least the ones we have for more then 35 years.

Back to the original question.
As someone said new components usually are more energy efficient and emits less heat, so if there where no overheating problem with the old cabinet the same functionality would work on a new one.

Today most cabinets whit great need of cooling is usually fitted with a heat exchanger, Rittal have several versions there are probably other brands too.
With these there is no air exchange from inside to outside of the cabinet, you put in your preferred temperature and they only run when needed and when you open the door it stops cooling.
Of course this is a more expensive solution at installation compared to installing a fan, but it saves on energy in the long run since it only runs when there is a need for it.



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein @ Dear Ms RedSnake (Electrical)8 Jan 23 08:33
" #1. ..... till pondering.... even with filters on the fan, more dust will be pulled in when you open the door if the fan is at the bottom. And for the function ....... they still have done the job at ...... for more then 35 years."
Look at thousands/millions of VFDs on the market:
(a) those with plastic enclosure are NOT intended to be in (normal operation) with [the enclosure/cover removed]; even with the [fan is still in position/operation!].
(b) for those with higher kW rating with enclosure say 2m in height or with multiple panels, they are NOT intended to be [in normal operation with the doors open]. The doors if open for testing etc. are of very short duration (say within <1h). Any dust drawn in, during this short time is minimal.

" #2. ......Back to the original question. As someone said new components usually are more energy efficient and emits less heat, so if there where no overheating problem with the old cabinet the same functionality would work on a new one...."
If the design was with the cooling air entering from the bottom and hot air is discharge/exhaust through the top, (i.e. with better heat ex-changing); a smaller kW fan ,or no fan is required. Ultimately save fan running cost.

" #3. .....Today most cabinets whit great need of cooling is usually fitted with a heat exchanger, ...... . With these there is no air exchange from inside to outside of the cabinet, ....... only run when needed...... is a more expensive solution at installation compared to installing a fan, but it saves on energy in the long run since it only runs when there is a need for it."
(a) Thousands/millions of single plastic enclosed (small kW )VFD are NOT installed with [externally mounted/attach heat-exchange]. Reason: One or tow/three fans are adequate. See also below FYI.
FYI: (a) Externally/attach mounted heat exchangers are NOT useful on plastic covers. They are to be mounted on metallic (i.e. high heat conduction material) panels.
(b) Extremal heat exchanger are expensive. Very very low efficiency, as the cooling effect is "indirect" (i.e. going through cooling the metallic panel to cool down the heat generating parts attached on the panel)
(c) All heat exchangers work on same basic principle : cool air enters from bottom with hot air exhaust through the top. NOT reverse.
(d) when the heat generated is very low and the metallic enclosure is very large plus if the environmental temperature is low (i.e. temperature difference is high); NO fan is required.
Che Kuan Yau (Singapore)




Thank you Red Snake, Gr8blu, Che, Jraef, CompositePro, Lional, mparentau, and Ed Stainless for your detailed responses.

My take is that while physics dictates that the most efficient cooling would occur if we put intake filters at a lower position and use the fan to suck air out of the panel at the top (making the inside of the panel negative relative to the room), the panel might stay cleaner if I stick with the current arrangement where we push cool air in from the top and allow it to exhaust at a lower location (making the inside of the panel positive relative to the room, which is the arrangement in my existing panel).

The ideas of a "fins out design" for my SCR's is interesting, but the location for this panel will be pushed right against a wall, so I think "fins out" might be difficult in my case. I think mounting the SCR's directly on the inside of the enclosure and using the enclosure itself as the heat might be less than ideal for me for this same reason. (Also, the enclosures I typically use come with a panel that is offset a small distance from the back enclosure wall, so I usually mount my components on this panel rather than directly on the enclosure wall).

I do believe (in fact, I am fairly certain) that the new components I use in this new panel will generate less heat than the old components in the old panel, and I have observed no sign that the old panel has been getting excessively hot. I suspect that I will have no over-heating issues whatever I choose.

Lionel's point that UL does not typically like openings on top is well taken also. This makes sense, as I have had panels in locations that I believed to be totally out of harms way, and water somehow found its way in as a result of an unexpected event.

Thanks to you all, I feel like I am in a much better position to make an informed decision on how I proceed. I still have some work to do on my actual layout. I'll make the final decision where I'll put my fans and intakes after I get a little farther with that.

I really appreciate all of your help.

Thanks again,
Paul Some thoughts about optimal cooling:
Hot air rises.
Yes, absent any other influence, hot air rises. Hot air expands, and the specific gravity drops, hence, the hotter, light3er air rises above the cooler, denser air. The effect is called convection.
It doesn't take much of a fan to overcome convection, and in the case of an fan cooled electrical panel, I tend to ignore convection.
Where to direct the incoming air?
All else being equal, although that is seldom the case, I would direct the cooling air first owards the hottest components.
With the cooling air stopped, the various components will be at different temperatures depending on the internal heat generated by each component.
The greater the difference between the cooling air and a particular component, the greater the cooling, or temperature drop of the component.
With the air directed first to the hottest components, they will experience the greatest cooling or temperature drop. As the air continues over the cooler components, it will have been warmed by the hotter components and the temperature difference and the cooling effect will be less.
With the air directed first to the cooler components, the air will be heated somewhat before it reaches the hotter components. There will be less temperature difference and thus less cooling.
So, comparing air first to the hottest parts with air first to the coolestparts:
Air first to the hottest parts, the hotter parts will run cooler and the cooler parts will run hotter.
Air first to the cooler parts, the cooler parts will run cooler and the hotter parts will run hotter.
How much hotter or cooler?
Probably not enough to worry about.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

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