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  1. #1
    Join Date
    Jun 2004
    Posts
    956
    Good day guys,
    I've just been moved into a building with the hot/cold wells in the system.

    I have the basic understanding how they work and why they are there but I saw something the other day and the senior operators have no clue what to say about it.

    The cold well usually runs a higher water level and will dump into the hot side, great, its cooling the hot down before it goes to the tower.

    The other day the hot side was high and dumping into the cold, raising the temp enough to cause alarms on the BAS.

    They think the water makeup was sticking and caussing the switch but I dont buy it. If there is too much water shouldnt both wells be high.

    Sorry for the long post but I like to know the equipment we work with, and get better answers here than from the guys at work.

  2. #2
    Join Date
    Oct 2001
    Posts
    6,956
    if the tower pumps go off for any reason won't the riser dump back down into the well on the hot side and alarm the BAS with hi cold well temps.does the chilled water depend on the hot well over flow to stay solid and does that dump back along with the condenser side
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  3. #3
    Join Date
    Jun 2004
    Posts
    956
    Originally posted by maxster
    if the tower pumps go off for any reason won't the riser dump back down into the well on the hot side and alarm the BAS with hi cold well temps.does the chilled water depend on the hot well over flow to stay solid and does that dump back along with the condenser side
    if the pumps go off it does dump back to the hot well

    3 way valve will short cycle water from the condenser outlet to the inlet if the water from the tower/cold well is to cold.

    this system normally has the cold well dumping into the hotwell, but a couple times has reversed to hotwel;l dumping into cold well and the guys cant explain why

  4. #4
    Join Date
    Feb 2006
    Location
    Lexington, Ky
    Posts
    169
    Let's pretend that the design conditions for the hot well/cold well system are:

    1000 gpm of pump for the cold well.
    1000 gpm of pump for the hot well.

    The normal sequence of operation is to start the hot well pump/s first, then the cooling tower fan/s to maintain the setpoint in the cold well. The cold well pump/s come on to maintain required flow to a process/chiller/HX.

    On a design day you might have all pumps (hot and cold) running to supply the needs of the facility. The hot and cold wells will have some steady level in each sump.

    If there is a reduction in flow (draw) from the cold well (maybe a chiller and its pump was shut down)to 500 gpm. The cold well will begin to rise and then spill over into the hot well.

    If, for some reason the hot well pumps shut down and water is not being pumped over the tower, the hot well will rise and spill over into the cold well.

    If the temperature controls are workng properly the water temp in the cold well will rise and bring on the hot well pump/s.

    Hope this helps.

  5. #5
    Join Date
    Jun 2004
    Posts
    956
    Enart
    that all makes sense to me.

    on this day all the pumps were running, it was a very hot and humid day and the hot well level is what went high, causing alarms for cold well high temp.

    I was thinking st causing lower flow but everything went back to normal the next day

    the senior guy thinks its because there was too much water, the float was sticking and make up wass going almost constantly. I think if there was too much water then both wells would be high.

    they dont want to dig and get the info, if everything is still running they are fine with that, they have 20 years on site and it seems I have alot of questions they dont have answers to.

    Do you guys know where I can get tech lit on systems such as these?




  6. #6
    Join Date
    Feb 2006
    Location
    Lexington, Ky
    Posts
    169
    Operator, I don't know where you can get any tech lit on this "system", but you should be able to find plenty of info on the individual components. Once you find that, start doing some "what ifs".

    Ex; what if someone turned on another pump from the cold well and I started removing 1300 gpm?

    what if I was only drawing 800 gpm from the hot well because I had a restricted strainer?

    what if, on a design day, the cooling tower is evaporating 1000 gallons of water per hour?

    what if the cooling tower started overflowing and someone closed down on a valve going to the hot deck to stop it from overflowing?

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