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Can a 4 Pipe System share a common Compression Tank?

JUGHNE Member Posts: 11,089
Hospital went from a 2 pipe system to 4 pipe.
They have a chiller with glycol and heated glycol from steam boiler heat exchanger.

The maintenance man pointed out that there is only one compression tank for both heating and cooling.
The water level in the sight glass used to be higher before the change over.

From the piping it looks like both the hot and cooling water are somehow connected together via the tank.

Is this standard procedure?


  • Jamie Hall
    Jamie Hall Member Posts: 23,536
    I wouldn't know what standard procedure was -- but if the tank can connect to both systems at all times, I can't see a problem with it. The water in the tank doesn't circulate, after all. The one trick would be making sure that any air which was wondering around in either system could make it to the tank.

    Do you have an automatic air valve on that tank? Many larger tanks do, and that should be holding your water level.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,341
    4 pipe like this?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JUGHNE Member Posts: 11,089
    Not sure about all piping.

    But chiller for cooling and steam tube in shell for hot water glyco.

    The steamer has to run for reheat in certain areas.

    I can look more in a couple of days.
    EBEBRATT-Ed Member Posts: 15,737
    No. Not standard procedure at all. Wrong.

    I would assume the existing expansion tank was sized for heating when they ran it as a 2pipe system because the expansion on chilled water is not much. It maxes out when the chiller goes down!

    If they added a lot of pipe converting from 2-4 pipe that would explain an expansion tank issue. If the original 2 pipe system is now the Heating zone the expansion tank is probably ok for that.

    Now that they have added chilled water pumps and more pipe & glycol it's a completely different animal.

    The chilled water side needs it's own tank. It should be two separate systems.

    2 pipe disadvantage is you can't cool and heat at the same time. Hospitals with high heat loads in computer rooms operating rooms etc need cooling year round in some spaces
    JUGHNE Member Posts: 11,089
    Thanks to all.

    To me, this seems like a cross connection between hot and cold.

    I will look at it again.

    I shouldn't even worry about this....but curiosity.

    All installed by engineers and pros from the cities, at least a 100 miles away.