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  1. #1
    Join Date
    Jul 2011
    Location
    Charlotte, NC
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    Extremely Low Hot Water Flow Through Fan/Coil Unit

    I have a 4-pipe heating/cooling system in a church. One of the fan/coil units is experiencing extremely low flow rate through the hot water coil. All the other fan/coil units work OK. I have blown high-pressure air through the problem coil and feel confident that the coil is not blocked. What are problems that could inhibit water flow through a how water coil that is not blocked? Any ideas would be apopreciated.

  2. #2
    Join Date
    Feb 2011
    Location
    Chicagoland
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    77
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    Appears to be blockage before, or after, the coil then. Find a good thermal camera, or at least a thermocouple thermometer, and take some measures.

  3. #3
    Join Date
    Aug 2006
    Posts
    3,228
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    Trying blowing Regulated Nitrogen or CO2 through the coil with the supply and return valves open. Have the Gas enter on the Supply side, or through the Bleeder opening. Blow compressed gas through an empty coil isn't going to do anything.
    Retired, after 43 Years

  4. #4
    Join Date
    Jul 2011
    Location
    Charlotte, NC
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    Thread Starter
    Thanks....I can try to get Regulated Nitrogen of CO2 to do this. Also curious about why blowing compressed air through the coil would not do anything??

  5. #5
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    23,065
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    Quote Originally Posted by Joe Howell View Post
    I have a 4-pipe heating/cooling system in a church. One of the fan/coil units is experiencing extremely low flow rate through the hot water coil. All the other fan/coil units work OK. I have blown high-pressure air through the problem coil and feel confident that the coil is not blocked. What are problems that could inhibit water flow through a how water coil that is not blocked? Any ideas would be apopreciated.
    Is it the coil or the supply return piping?
    Pressure gauges and thermometers are needed!

  6. #6
    Join Date
    Jul 2011
    Location
    Charlotte, NC
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    Thread Starter
    It is the coil. There is plenty of flow through the hot water bypass pipe when the thermostat is not calling for heat.
    However, when the thermostat calls for heat, the inlet pipe to the coil becomes hot and the coil becomes warm on the bottom (near the inlet), but becomes progressively cooler toward the top of the coil where the outlet pipe is. It seems that the flow is restricted.

  7. #7
    Join Date
    Dec 2014
    Location
    New Mexico
    Posts
    927
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    Pull the coil out and take it outside, pipe it up so you can flush it with a hose both directions it to a bucket to catch what ever is causing the blockage. That way the water treatment company can address the root problem. The flush with a hose provides enough volume to get in to each pass. The unit should have a tag stating max pressure more then likely since one end is going into a bucket you won’t exceed that pressure. Trust me take it out side if you try it in place you don’t have enough rags to clean up the mess when the loose hose comes out of the bucket.


    Sent from my iPad using Tapatalk

  8. #8
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
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    Since you mention hot water bypass pipe, I take it that the coil has a three-way valve. Is it operating properly? Is it properly installed, with the ports piped up to the proper connections?

  9. #9
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
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    Quote Originally Posted by Joe Howell View Post
    It is the coil. There is plenty of flow through the hot water bypass pipe when the thermostat is not calling for heat.
    How do you know the GPM's? Are there pressure gauges?


    I agree with Nuclrchiller Could be an issue with the control valve!

  10. #10
    Join Date
    Jul 2011
    Location
    Charlotte, NC
    Posts
    17
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    Thread Starter
    Yes, you are right about it having a 3-way valve for hot-water bypass. This valve is installed and operating properly.

  11. #11
    Join Date
    Dec 2004
    Location
    Chicago area
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    Quote Originally Posted by Joe Howell View Post
    Yes, you are right about it having a 3-way valve for hot-water bypass. This valve is installed and operating properly.
    Can you draw out the piping, all the way back to the source of the supply and return.

    Start there.

    Perhaps a strainer is clogged.

    Its almost impossible to tell if flow is good during bypass.

    Also - is this coil larger or different in some way from the others.

    Is the valve on the supply side or the return side.

    Has it been replaced recently?



    Sent from my iPhone using Tapatalk

  12. #12
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
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    Is there a balancing valve?


    Sent from my iPhone using Tapatalk

  13. #13
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    7,878
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    Whats the system pressure, and how high up is the coil?


    Sent from my iPhone using Tapatalk

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