DDC vs. Pneumatic
I will be meeting with a customer next week too discuss his control options. It is an industrial building that doesn't need real high end control over the temp.. I am thinking of pushing the pneumatic because of the low maintenance and how long it will last. It is not necessarily a hazordous building, but if they go DDC I will suggest explosion proof in many areas because of the high temps., it is a foundry. Does anyone have any drawbacks to pneumatic that I should consider? An example being the lack of techs. trained in servicing pneumatics.
What comes to mind is if the customer would want remote capabilities, even from within the plant, DDC would be the better way to go.
Maybe I am missing something but I've always considered DDC low maintenance, if installed correctly, when compared to pneumatic. No compressor oil changes, no air lines to worry about leaking, no air dryers, no drain valves, no drain valve controls, etc. The other thing is I know of DDC systems that are over 25 years old still running strong. Granted I know of pneumatic systems running longer than that, but most older pneumatic systems I've come across have been poorly maintained. Pulled out one pneumatic system for DDC that was about 18 years old, but it was pretty. The maintenance guys kept things in top shape, I was actually kind of sad ripping it out, cause it was such a showpiece.
For an industrial application they may have clean air running all over the place already and it makes it an easier tie in. The other thing is the timing needed for any valves - pneumatic is still faster and less expensive than an electric valve overall.
The major drawback is that if they want to do any trending, remote monitoring/control, alarming, etc. you will then have to have some kind of interface on top of the pneumatic.
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Being a foundry I would guess they do a fair bit of exhaust ventilation. Depending on the situation they might see some cost savings tying them into a DDC system in the future.
1.Draw backs, small labor pool with actual knowledge of "Pneumatic Controls". Compressor Maintenence for that Clean dry Air.
I would suggest a Hybrid of Pneumatics and DDC. Use Pneumatic Valves/Actuators and run E to P transducers via DDC. You get the power and speed of Pneumatics with the "Fancy" capabilities associated with DDC like remote access, graphics, Trending, email/text alarm notifications and so on.
But you still have the compressor to maintain. It is a small peice of the system yet still very critical. Use a duplex compressor and life should be good !
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Hmmm. Explosion proof? I'm trying to wrap my mind around your thinking here.
Originally Posted by Big Unit
Just how hot are the places you'll be running control lines (either pneumatic or electrical)?
I've never done HVAC controls work for a foundry, but I've been in one numerous times. (Father-in-law used to be the general foreman of one and I spent some time there with him as I found it interesting. I'm one of those idiots who just likes to find out how stuff works.)
In any event, I never saw any of the HVAC controls that were located in any place hotter than a human being being could tolerate. Actually, in general, the foundry he worked in, and several others he took me on a tour of, weren't any hotter in most spots than many a boiler room I've been in.
In any event, I'd presume none of the actual HVAC controls and equipment would be located just all that close to furnaces, pour pots, etc. And right now I have DDC controllers that have been installed in older ... hotter ... boiler rooms since the late 1990's. Some of them running 120 - 130'F on average. With control electrical cabling running through areas (to valve motors, damper motors, etc) that are probably 30 to 50 degrees hotter. Hot enough so that one time I was checking a valve actuator while standing on the top of an operating boiler and had the problem of slipping and sliding because the heat was melting the soles of the shoes I was wearing at the time.
Certainly, under such conditions we keep the controllers themselves away from the worst of the heat, install them in the "cool" areas. And installed in decent cabinets to minimize chances they'll get splashed upon by liquids or collect excessive amounts of dust, grit from grinding operations, or whatever. Not explosion proof cabinets, just ones that close tightly, have vent holes on the sides (top and bottom), with the downward angled slats.
In cases where we have to turn on or off a fan or motor that is itself in a really hazardous location, we'll typically do so by placing a contactor or relay at the LC or breaker panel rather than running a control line into that hazardous location, whenever possible.
In any event, I've nothing against pneumatics except the thoughts already expressed by others in this thread. Pneumatic controls can work fine, despite their disadvantages.