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  1. #1
    Join Date
    Aug 2012
    Location
    Coal Country
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    6

    Question AIR! in a Closed loop chilled water system

    After replacing two redundant chilled water pumps we have had constant air on one side of our chiller plant. The pumps and piping were refilled up to the check valves after recommisioning. Our tech's bleed the air off and 48 hrs later it is back. luckily it hasn't moved to the rest of the system. Is there anyway to find the air leak on the suction side of the pumps? Other ideas?

  2. #2
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    2,063
    "Up to the check valves" doesn't tell us anything since we don't know the layout of your system. How many stories in height does your chill water system go, and where are the pumps located? Especially location as related to the height of the system. Verify there is no part of the system that is at a negative pressure, or a vacuum. Are you certain that air being removed is not simply residual air that was introduced during repairs?

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Are there gauges on the pumps? Is there enough net positive suction head (NPSH) on each pump? Pumps not cavitating?

    Do you have automatic air bleeding devices on the loop, especially in the plant where the air is collecting? And if so, have they been checked to be sure they're not clogged or faulty?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Aug 2012
    Location
    Coal Country
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    We are not sure that it is not residual. But we have been bleeding a ton of air over the last month. The check valves are installed about 3ft above the pumps. The check valves are above the vibration dampeners and a 10" to 8" reducer. We have a primary secondary chilled water system. The inlet side of the pump is definitely at a negetive pressure at the decoupler. the decoupler can swing positive or negative pressure.

  5. #5
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    2,063
    Sounds as though you probably have a leak at or near the inlet of the pump. Since it is at a negative pressure, it is sucking air, instead of leaking out water. Try adjusting the make-up water regulating valve to maintain a positive pressure at the point of the lowest pressure in the system, which is quite possibly the pump inlet. But first, make sure the negative pressure is not a result of a restriction, like a dirty strainer or a (partially) closed valve.

  6. #6
    Join Date
    Aug 2012
    Location
    Coal Country
    Posts
    6
    Pumps are running great no cavitation. The engineer who designed the system put air bleeders in all the wrong places. The air seperators are working but not picking ithe air up. The air is staying in one high spot on the primary loop. The primary loop is 15 ft above the replaced pumps and is the same elevation all the way around the chiller room.

    I am sorry if i am not being clear, it is a little stressful the equipment is mission critical and we can't loose this cooling. THANKS FOR ALL YOUR HELP EVERYONE!

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    You said the pumps are "running great", but do you have gauges on both sides of the pump to indicate exactly how great they're doing?

    Are these primary chilled water pumps, or secondary?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Hot Tap bleeders into the section thats collecting air. Simple solution.

  9. #9
    Join Date
    Aug 2012
    Location
    Coal Country
    Posts
    6
    The inlet gauge on the pump reads 5 psi and the outlet reads 30 psi. I am judging the performance on amp draw vs. flow rate. The pumps pull water off the primary loop to feed the secondary loop. We are suspecting a bad guage and are replacing all gauges.

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Out of curiosity, you are suspecting a "bad gauge" for what reason?

    I've had good experiences with liquid filled gauges as replacements. Eliminates needle flutter and seem to last longer.

    Now, where the air is gathering, is this on the primary or secondary loop?

    I agree with the hot tap air bleeder suggestion. Do you also have a water meter on the make-up water to the loop? ALWAYS good to have that, so you know if you have a leak.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #11
    Join Date
    Aug 2012
    Location
    Coal Country
    Posts
    6
    Our facility managment team frowns against this idea. i don't know why. Probably cause they don't understand it. Thanks for the suggestion

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Frowns against which idea...the hot tap or the make-up meter?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    Aug 2012
    Location
    Coal Country
    Posts
    6
    Air is gathering in the primary loop right before the piping turns and drops 15' down to the pump inlet at floor level.

    They love the make up water meter suggestion. But, the term " Hot tap" is like a curse word around here. We have ordered liquid filled gauges and suspect the faulty inlet pressure caused one of our tech's not to add enough make up water. Now that we do not have negetive pressure on the inlet to the pump hopefully the air will stop. It is a waiting game to see if the air returns.

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