Fan in an electrical cabinet

We have a customer that spec's that every electrical cabinet have a fan with filter communicating with the outside.

This machine is going to have a starter, brick plc and a few terminals and fuses. In this case it is completely unnecessary.

I have spent quite a bit of time in their plant and control cabinets, and every one is full of ****. They never maintain the filters. The are a machining environment with lots of coolant splashing around.


I am not asking about this specific situation, but it got me thinking. What are other's experiences with fans and other cooling mechanisms? My opinion is that in dirty environments, you would never want outside air going into a cabinet. I would prefer a closed system like an air conditioner or heat exchanger.

How do you people look at it? My perspective is as an OEM, so I don't have to live with the stuff. I would like to know what it is like to live with it.

I have worked both sides of this particular fence, and agree with you whole-heartedly. The spec to have cooling on virtually all cabinets is, on the surface, a good one but, as with just about every across-the-board mandate, it is a bit short sighted to require "fan cooling".

On the other hand, my experience with air condtioners is tough environments isn't much better. They, too, have filters that no one will keep clean. They do keep the cabinet cleaner, though.

I don't have a lot of personal experience with heat exchangers, but they seem like the right piece for this portion of the puzzle. I have seen some that look pretty promising. And since most electronics are more than happy to run at even the most uncomfortable of ambient room temperatures, they sound even better still.

That's my 1-1/2 cents.

Steve

Pros and cons

I agree that fans are a poor solution for heat dissipation in a dirty environment.

Natural ventilation is often better: less filth forcibly collected. Drip proof or baffled air inlets and outlets work well to allow natural circulation and have the advantage of no moving parts to break or wear out.

As far as the chiller option goes the main diadvantages I have experienced are:
If it is in a humid climate/environment the condensation may pose unforeseen problems (e.g. dripping into a control pc...)
It will fail in winter and the end user won't figure this out until they have real problems in midsummer.

Heres my two cents..... Ultimately they dont last. Bottom line. They are in theory good, but down the road they will be disconnected or yanked out completely, speaking of fans. A/C is nice if you can afford it and if you maintain it. I prefer to exhaust the air from the cabinet. I have worked in alot of places and fans are the least maintained of all. However we make the fan housing for cabinet fans that you find in grainger, so, keep using them please, ha ha.

Ed

If shop air (compressed air) is available I've always thought the vortex coolers such as sold by AutomationDirect.com (W750400 for example) were a pretty slick solution.

Tom Jenkins said:

If shop air (compressed air) is available I've always thought the vortex coolers such as sold by AutomationDirect.com (W750400 for example) were a pretty slick solution.

Click to expand...

Are they expensive to run?

I've been thinking about some sort of venting system that would just use natural convection to circulate the air but you run into the same filter neglect as you do with a/c units. pretty tough to get around neglect

The natural convection approach will gather some dust but not as much as forced flow. If you add filters at all they could be a metal mesh variety that could be cleaned with air or just whacked.

Just a thought from the maintenance side.

I learned a lesson long time ago, never, never, never put any holes in the top of a cabinet. Heat exchangers, air conditioners, conduits will drip condensation. Conduits can actually pipe water in from outside via a leaky cover or fitting. Vortex & mill air will introduce moisture and oil into the cabinet. If you must have holes in the top then lay them out as to drip behind the cabinet backplane.
One solution that fits all will not work, different fix for different situations. Proper engineering from the start will help a great deal, size of cabinet, type of cabinet, location of cabinet, location of power supplies and other heat producing components in the cabinet. Even module placement in a chassis will be a big help in keeping heat away from the PLC. In using PLC-5 PLCs, when using a in-slot power supply, place it in module group seven, one reason is to keep the produced heat away from the PLC and another is you can select not to scan module group seven. No sense in scanning a power supply(s). There is never time to do proper maintenance, maintenance is a necessary overhead.

Roger

In the places I've worked I have seen the use of the buildings' air conditioning, self-contained air condioning, muffin fans, thermostatic controlled muffin fans and nothing at all. I liked the building air conditioning with a simple damper controll the best as the cabinets are very clean. The self-contained units are ok until they fail. Muffin fans are the most common but of course the inside of the cabinets soon collect particles from the outside of it. We always put a small ribbon on the muffin fans so you can tell if they're working or not. The thermostatic controlled units would be the most energy efficient, aside from nothing if they're not needed, but we're not talking huge savings here! I haven't seen the vortex coolers Tom Jenkins mentioned but they sound very interesting and I will check them out. As far as maintaining any piece of equipment, I'm sure your competitors would encourage you not to...

I've used the vortex coolers from Exair (http://www.exair.com/cabinetcooler/cc_page.htm) for a while now with very good results. They have several sizes and some pretty good reading on air usage and cost.

They are a bit noisy but the price was right.


Bob

be sure to use a water/oil filter on these.

Why not use Solid State AC units
No Filters , No air exchange inside to outside
No moving parts
I have been using them for years on mill cranes, best thing we ever did.

GSI1:
Do you have an example (or several maybe) of a supplier of solid state air conditioning units ?

To all:
I use "augmented convection".
Thats simply a fan inside the cabinet to increase the natural convection.
Not as effective as outside air or air conditioners, but there are no openings to the outside. So there are no filters to clean.
The heat dissipation should be 25-35% increased as compared to natural convection, but I think that the effect is quite a bit greater, as the fan evens out the temperature difference between the top and bottom of the panel. As the PLC and HMI is typically placed in the top of the panel (and they are the most temperature sensitive parts), this also betters the situation.

GSI1 said:

Why not use Solid State AC units
No Filters , No air exchange inside to outside
No moving parts
I have been using them for years on mill cranes, best thing we ever did.

Click to expand...

Do you have more info?

I just did a Google search using "solid state""air conditioning" and got quite a few good hits.

Looks like a pretty good solution too. I think I will give one of these a shot on a system I am getting ready to build.

Thanks for the idea GSI1.

Steve