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  1. #1
    Join Date
    Nov 2010
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    166

    3 Pipe Unit Ventilators

    As with the other subjects of interest, such as boilers, chillers etc, I thought I'd start a thread to answer questions regarding the old pneumatic 3 pipe systems that are rarely ever seen.

    I have attached a picture below. What exactly am I looking at? I know it’s a Unit ventilator of some kind, is it three pipe etc? What are the two small doors near the grill used for (one is on the right, one on the left)? Are these systems strictly pneumatic, and seen only in older installations? I don’t see these units in new construction, when did this style unit go out of favor with architects. Are any still made today?

    NOTE: I’m not talking about the “hotel units’, which look similar but function on their own. I believe the system I’m referring to requires a boiler/chiller to operate as the door on the left typically reveals pipes going into the wall.

    I apologize if this has already been discussed.

    Thank you
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  2. #2
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,415
    I get to work on a ton of unit ventilators, so they are still made, and quite popular in the schools around here.

    The older ones are likely pneumatic, but the new one's do have the fancy flashy box controls too.

    The one's I run into are usually a 2 pipe or 4 pipe, can't say that there's many 3 pipe one's around here, but I'm sure there are a few I forget about.

    The doors on the top, generally... one side is fan controls and the on off switch, the other side is usually for the illusion of being able to work on something with out tearing the unit apart. That door works good to open and stick your ear in when you're lookin for an air leak though.

    Some of them are horrible to work on, they put a freeze stat clear in the back, or a low limit control buried under a valve. I know there's not a lot of room in these, but man you'd think they'd at least lay them out a little better.
    The one's with digital controls in them are a bit better usually since there's less stuff, or less bulky stuff in there like some pneumatic one's have.
    "If you call that hard work, a koala’s life would look heroic."

  3. #3
    Join Date
    Nov 2010
    Posts
    166
    Quote Originally Posted by amickracing View Post
    I get to work on a ton of unit ventilators, so they are still made, and quite popular in the schools around here.

    The older ones are likely pneumatic, but the new one's do have the fancy flashy box controls too.

    The one's I run into are usually a 2 pipe or 4 pipe, can't say that there's many 3 pipe one's around here, but I'm sure there are a few I forget about.

    The doors on the top, generally... one side is fan controls and the on off switch, the other side is usually for the illusion of being able to work on something with out tearing the unit apart. That door works good to open and stick your ear in when you're lookin for an air leak though.

    Some of them are horrible to work on, they put a freeze stat clear in the back, or a low limit control buried under a valve. I know there's not a lot of room in these, but man you'd think they'd at least lay them out a little better.
    The one's with digital controls in them are a bit better usually since there's less stuff, or less bulky stuff in there like some pneumatic one's have.
    Who makes the "new" unit ventilators? I'm still fairly sure that they are not included in most new construction; they are probably made to be used as replacements.

    Do any of the “new” univents NOT have the “flashy controls”? I’m looking for the standard units with the basic; Hi, Med, Low knob. The standard univent would also need to incude pipes to the boiler. Are these still made?

    Thanks

  4. #4
    Join Date
    Oct 2005
    Location
    Phila
    Posts
    118
    There are lots of unit vents still out there. Marvaire, Trane, McQuay AAF are just a few. I am told you can still special order Nesbitt if you want one. But that looks like an airtherm cab heater to me.

  5. #5
    Join Date
    Nov 2010
    Posts
    166
    What's an "airtherm cab"? Is it a type of univent?

    To be more specific; I'm looking for a new FLOOR MOUNT univent, such as the one in my picture. NOT an RTU unit ventilator.

    I'm looking for a basic floor mount univent with; a Hi, Med, Low knob, and an access door on the other side. No need for the flashy controls, just the three basic settings compatible with a 3 pipe system. Does anyone know what I’m referring to?

    Just out of curiosity, when were these phased out in favor of the new RTU unit vents? I know 3 pipe systems aren’t manufactured anymore, when were they discontinued??

    Thank you,

  6. #6
    Join Date
    Oct 2005
    Location
    Phila
    Posts
    118
    http://airthermhvac.com/

    A unit ventilator has a controlled outside air damper.
    A fan coil and cab heater have a 2 position or no OAD.
    In that picture it looks like an airtherm fancoil/cabheater.

  7. #7
    Join Date
    Dec 2005
    Location
    Spokane Wa
    Posts
    169
    typical 3 pipe system consists of chill water going to 3 way valve port. Hot water to the 2nd port of the valve and a 3rd port goes to the inlet of the coil. There is only one coil. The return water is usually common to the hot water and chill water. Pneumatic acuator on the valve. Those are labled school room fan coils. The left door usually has the pneumatic 3 port valve buried in there and the right door is controls. It will probably have a belt drive fan.

  8. #8
    Join Date
    Jul 2001
    Location
    Canada
    Posts
    1,827
    Up this way they have direct drive dual shaft motors ( 3 speed ) for the squirrel cage fans , belt drive is very rare

  9. #9
    Join Date
    Nov 2010
    Posts
    166
    Please eleaborate more on;

    three pipe, four pipe, 2 pipe etc

    Thank you

  10. #10
    Join Date
    Nov 2010
    Posts
    166
    Is it refrigerent/coolant or water going through the various 2,3,4 pipe systems?

  11. #11
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    Water

    2 pipe has a supply & return pipe. You get what the building is putting out. In the winter, hot water, in the summer, chilled water. This is the most common system, cheapest to install & run but least comfortable.

    3 pipe is rare. With it, hot water comes in 1 pipe, chilled in the 2nd and whatever you use gets returned to the mechanical room. That means the hot & chilled water is mixed together in the return system so the boiler & chiller have a lot more work to do.

    The most desirable is 4 pipe so in mixed weather, the space can have both heating & cooling as needed.

  12. #12
    Join Date
    Jul 2001
    Location
    maryland
    Posts
    1,355
    Never heard of 3 pipe until just now. Sounds silly to me, but I guess they did all kinds of wasteful things back in the day.
    Saving the world...one service call at a time.

  13. #13
    Join Date
    Nov 2010
    Posts
    166
    Quote Originally Posted by mallron View Post
    Never heard of 3 pipe until just now. Sounds silly to me, but I guess they did all kinds of wasteful things back in the day.
    Anybody have any information on when these systems went out of use? The only time I ever saw a 3 pipe system was in a building built in the early 1960s. Has anybody seen a later installation?

    Best

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