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  1. #1
    Join Date
    Nov 2019
    Posts
    1
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    VAVs making no sense

    I work in a hospital. We have about a dozen inpatient rooms. Each rooms temp is controlled by a vav. The hallway im having trouble with has 5 vavs for 5 individual rooms. They all operate off the same supply and return lines. However the two vavs on opposite ends of the hall will not provide a supply air temp anywhere close to warm enough to heat the rooms. Now the 3 in the middle are operating perfectly. Ive cleaned filters, removed a bunch of gunk. Still nothing. Supply water temp is still top cold at opposite ends of the hallway. Does anybody have even an inklinh why this would occur.

  2. #2
    Join Date
    Jun 2009
    Location
    Dallas/Fort Worth
    Posts
    3
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    If there’s cold air coming out of the supply grills for those rooms then all that tells me is that the damper is open, grab a ladder and flashlight, look above the ceiling where VAVs are located and see what’s providing heat for that particular room, could be electric heat strips, a hot water coil, steam coils, or maybe nothing connected to the VAV to heat the room at all??? Sorry just not enough info...

  3. #3
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,793
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    You are not getting hot water flow. Check for plugged strainers and nonfunctional valves or closed isolation valves.
    No man can be both ignorant and free.
    Thomas Jefferson

  4. #4
    Join Date
    Mar 2018
    Location
    Sumter, SC
    Posts
    726
    Post Likes
    Going to follow this thread. Just got a new job and have been working on VAV's this past week. I am new to them, and the control system we are using on them.

  5. #5
    Join Date
    Aug 2019
    Location
    Central Florida
    Posts
    105
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    Wayne is correct. Is this steam or hot water?

  6. #6
    Join Date
    Sep 2019
    Location
    Northern Ontario
    Posts
    58
    Post Likes
    Like others said, need more info. Ours are dual duct (hot air mixed with cold air). Few units have a hydronic heat coil after the vav to boost heating. Dampers and valves are operated by belimo actuators. So no power or signal to actuator? Or actuator bad? Had a couple set for wrong rotation from install 5 years ago.

  7. #7
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,793
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    His description fits single duct boxes with hydronic heat. The coil can be on the box inlet or outlet or duct mounted but on VAV'S they are almost always on the box outlet.. He said the pipe is cold indicating no flow. Dual duct VAV'S normally heat from a hot deck coming from the AHU so they seldom have heat coils.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. #8
    Join Date
    Jan 2013
    Location
    Central Arkansas
    Posts
    207
    Post Likes
    if they are hot water reheat check as others have said for isolation valves turned off, have done it when valve not closing off all the way, check for plugged strainer, bad actuator, bad valve

  9. #9
    Join Date
    Jul 2018
    Location
    Wisconsin
    Posts
    1,095
    Post Likes
    Strainer could be plugged. If it is a pneumatic damper actuator the diaphragm may be ruptured and the air flow may be to much for the coil to heat the air, or a combination of things.

    Sent from my SM-G960U using Tapatalk

  10. #10
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    289
    Post Likes
    Did you check the discharge temp of the two not working?

  11. #11
    Join Date
    May 2004
    Location
    SE Pennsylvania
    Posts
    1,903
    Post Likes
    Is the heating valve opening fully? Is the airflow set correctly and verified? Check the strainers and circuit setters for blockages. You stated you had changed filters. Were these in the VAV? If so that would tell me these are fan powered. If so, verify the fan airflow is correct.

  12. #12
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    7,059
    Post Likes
    KISS.

    If you have cold..... hot water pipes, you either don’t have flow, due to a restriction, valve, or air lock. Or you don’t have any water in the hot water loop.


    Wayne is correct....

  13. #13
    Join Date
    Aug 2019
    Location
    Central Florida
    Posts
    105
    Post Likes
    It would be nice if the OP would follow up here so we could all see where this is going.BTW....lots of good advice given above .

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