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What's the correct condensate level?

What's the proper water level (or range) for a condensate tank?

The gauge glass on our tank is always full past the top. Every time the condensate pump runs, a solenoid valve opens and cold water tops up the tank. Then I hear overflow running into the floor drain. I found the following in the paperwork from when the boiler was installed. It's from the consulting engineer who wrote the bid specs, when he was following up after installation.

"The water supply pump is directly connected to the condensing tank. There was a new by-pass line with shut off valve installed. Recommendation: Solenoid valve and water pump should be interlocked so that whenever the level in the condensing tank drops below set up value, the solenoid valve will open the water supply and at the same time signal from solenoid valve will engage pump to supply water to the boiler. This control must be installed for the proper boiler operation."

I would have thought that the condensate pump should run only when the condensate level is high, and that the make-up solenoid should only operate when the condensate is (extremely) low. It seems to me that now, every time the condensate pump puts water in the boiler and lowers the level in the tank, the make-up supply comes on, and runs the pump while also trying to refill the tank. So we get lots and lots of fresh cold oxygenated water in the system and too much water in the condensate tank, which overflows. No high water alarms from the boiler; just lots of cold water mixing with the condensate every 5 minutes or so. This can't be right?

Comments

  • Brad White
    Brad White Member Posts: 2,398
    Condensate Receiver vs. Boiler Feed Unit

    I think you have a piece of equipment trying to do two disparate things and they seem to be fighting each other.

    If set up as a boiler feed unit, the pumps will run on a low water condition at the boiler to top it off.

    If a conventional condensate pump, when it gets full, it empties itself regardless of what the boiler needs. (Nicole Ritchie comes to mind here.)

    What calls for the pumps to come on? High float or low boiler? I would start there.

    If you do have a need for a bona-fide boiler feed unit and a condensate tank, you can install another in series. The first would be sized for about 20 minutes of condensate storage, the so-called surge tank. This will hold the volume you generate until it is needed and would also receive cold water but only as needed. It acts as a buffer to absorb massive warm-up flow but also allows free air to vent out to a point, "deadening" the water. Some have a sparger tube to inject steam into it as a pre-warmer and rudimentary deaerator, but that is more of a commercial/institutional approach. (I do not know how big your facility is.)

    This surge tank then fills the boiler feed unit when it gets low. The boiler feed unit water level controller initiates this.

    You just have to set the boiler feed unit to only run on boiler low water and not give any cold water connection or response.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Stuart Rogers
    Stuart Rogers Member Posts: 49
    condensate vs boiler feed

    Thanks so much for responding, Brad.

    I'm working without much in the way of documentation on this system, trying to figure out how it has been set up. Mostly what I'm finding is things that are plain bad practice according to Mr. Holohan's "Lost Art" book. I'm in a 1925 co-op building with 25 apartments, original column-type rad's, and a 2-year old Weil McLain 1280 boiler. (President of the Board, trying to identify and fix the things that are costing us $40,000/year in natural gas.)

    I don't know yet whether it's a condensate pump or a boiler feed pump we've got -- not sure how to deduce that from what I see. But either way, it just seems wrong to me that there's fresh water entering the system every 5 minutes or so. Doesn't fresh water corrode everything pretty fast?

    I do see two low-water devices on the boiler, one higher than the other -- does that imply a boiler feed setup, or just a redundancy for safety? If it is a boiler feed, then shouldn't the water-makeup valve only operate when the condensate tank is almost empty? (It's never less than 100% full, now.)

    many thanks,
    Stuart
  • Brad White
    Brad White Member Posts: 2,398
    Stuart

    The units are outwardly identical in appearance, usually a cast iron receiver and one or two pumps mounted to the sides. What distinguishes them is what operates the pumps as we have been discussing- watch what happens when the boiler feed drops- that should trigger the pumps to go on as I would think.

    The water feed is your culprit. It sees an empty receiver as a sign of low system water and is not watching the right things. Yes, too much makeup water is detrimental to system life, you are correct. In my opinion, it should operate only after the receiver is empty (boiler being as satisfied as it can be made) but that the boiler is still low on water.

    A good electrician familiar with boiler controls would be worth calling. Watching the control actions and reactions is essential.

    The two devices on your boiler may be redundancy, hard to tell from here. You could post photos maybe?

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Stuart Rogers
    Stuart Rogers Member Posts: 49
    boiler-feed vs condensate

    Hi Brad, I finally found a good steam pro in Toronto, and had them round this a.m. They said (a) it's a boiler feed pump and (b) the higher of the two low-water sensors is controlling it. They also agree that the condensate tank & water feed are set up wrong, so we're getting way too much fresh water introduced. I sent them away to prepare a fullscale staged renovation plan of the system (add an outdoor temp. sensor to control boiler, fix traps, skim boiler, etc. etc.). I think I finally see some light at the end of this very hot tunnel!!

    Thanks so much for helping me understand our system,
    Stuart
  • Brad White
    Brad White Member Posts: 2,398
    I think

    that you are in very good hands. The use of OD controls, traps, skimming, all good indeed.

    Please post updates and what you see in terms of economy of operation or anything else of note.

    Cheers!

    Brad
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
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