Pneumatic thermostat question

Old 10-22-08, 04:02 PM
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Pneumatic thermostat question

At work our airhandlers use pneumatic thermostats, they work both the A/C and Steam heat. Is it possible to change them to electronic thermostats? If so, how hard is it? Is it something I can do myself?
Old 10-22-08, 05:25 PM
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Sure you can change them if you gain the knowledge to do so.

Your pneumatic thermostat will be connected to an air supply which through the thermostat operates operates a modulating valve to control steam.
If this is generally what you have you will have to pull everything out and go totally electric which would require electric modulating thermostats and steam valves.
You will likely have a ventilation system with pneumatic dampers where you would also have to pull the pneumatics out and use electric proportional damper motors with electric controllers.

My personal opinion is it would it would be easier to learn how the pneumatic system works and adjust it properly.
Pneumatics are old school but if set up properly are bullet proof and should require little service.
They absolutely must have a clean and dry air source which means an air dryer is necessary.

If you are asking this from a maintenance person perspective I would suggest that it would be a wise investment to hire a major controls company give you a tune up.
Old 10-22-08, 05:48 PM
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I went through a similar situation several years ago at my old workplace. We had a large building built in 1962 with a pneumatic system. For the most part, it was extremely reliable, but it did require periodic maintenance to keep it running at it's best. When energy costs began to skyrocket, they decided to replace the controls with a DDC (Direct Digital Control) system, but left all the actuators, etc..under pneumatic control. It did save the company a lot of money, but we determined that by simply keeping the pneumatics properly adjusted, that was the real money saver.
If your system is in generally good shape, as Greg said, keep the pneumatics. PROPERLY ADJUSTED, they ARE bulletproof. You could get estimates from a HVAC company to convert your controls, but generally, it is not a simple job.

Here is a nice (but 28 pages long) general link illustrating typical pneumatic principles:
Old 10-22-08, 07:57 PM
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While I disagree with the statements of pneumatic systems being bullet proof I will agree that changing a pneumatic system to electronic would be a HUGE expense with very little gain.

One of the nice things about an all-electronic system is that they usually work or they don't. There is very little chance of their "sort of" working. The same is definitely NOT true of pneumatic systems. As the others have stated, a pneumatic system REQUIRES clean, dry air to operate well. Dirt and oil in the air are the two main reasons for a pneumatic system's operation to degrade over time. Often this degradation is so slow that you never notice it until finally the system either refuses to work or it works erratically or with poor control.

The good thing about pneumatics is they are fairly easy to understand with a little study and the tools needed to test, repair and calibrate them are fairly inexpensive.
Old 10-23-08, 09:15 AM
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Thanks guys, I appreciate all the advice and I'm going to follow it. I'm going to leave it as is and just get a tune up on them.
Again, Thank you.

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