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make-up water from DHW??

Tom R.
Tom R. Member Posts: 139
When you say the tank is too small, we would think that it runs over sometimes, and runs dry at others. Otherwise introducing make-up water at half full is normal, compensating for leaks in the system. If the boiler takes on more water than the tank has in inventory in one feed cycle, move the float point of control up higher and widen the start/stop distance on the float. Another option is to regulate the boiler level more closely. This will cause the boiler feed pumps to start and stop more often, but will result in taking less condensate from the tank at one time. The size of the tank is based upon the amount of condensate returned from the system in a boiler idle condition, which should be more than required to maintain the level of water in the boiler. As the tank level only should change several inches each time the make-up valve opens, the total temperature of the water entering the boiler is not affected much. Should you find the make-up water on frequently, you either have abnormal leakage, or a process that does not return condensate. BTW, what pressure does the boiler operate at?

Comments

  • Stuart Rogers
    Stuart Rogers Member Posts: 49
    cold or hot make-up water to steamer?

    This seems like such a good idea, yet I've seen no discussion or suggestion about it... so I wonder why it's not standard practice.

    We have a WM 1280 boiler with a too-small condensate tank (not by much). When it gets about half empty, a float valve introduces cold water from the municipal supply.

    I've suggested to our steam fitters that (since we have to install a backflow preventer anyway) we should source the make-up water from the nearby domestic hot water tanks, rather than the incoming cold water supply. Wouldn't this be easier on the steam system? Cheaper, since we've already heated hundreds of gallons of water to 120 F and only need 2-3 gal. of make-up supply. The make-up water would be free of oxygen, and pre-heated to prevent thermal shock.

    Any potential problems?
    Why wouldn't this be standard practice?

    thanks!

    (By the way, later on I will post the results of our rehabilitation project, begun in mid-December. I can tell you today that we are paying a FRACTION of last year's gas bill!!)

    gratefully,
    Stuart
  • gerry gill
    gerry gill Member Posts: 3,078
    we use hot water

    often..but..the feeder has to be rated for hot water temperatures..most mechanical feeders are not..many electronic feeders are..slantfin boiler company actually recommends this in some of their literature..we do it cause the hot water contains less air..

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  • Stuart Rogers
    Stuart Rogers Member Posts: 49
    but it's sitting in hot condensate, isn't it?

    Thanks, Gerry, but I'm confused. The feeder mechanism is just a float valve inside the condensate tank, so whenever the system is running, it's sitting in 160+ deg. water; the DHW supply is only about 120 deg.

    There is a couple of electronic valves on the supply line a few feet from the tank, but I understand it's some kind of safety measure. If I remember what our contractor told me, the idea is that if the condensate tank approaches empty, the safety controls would shut down the feed so that the boiler would not suffer thermal shock from having only cold water pumped into it straight from the make-up supply. Is this the device you're referring to that has to be rated for hot water temps? (pix attached.)

    thanks!

    stuart
  • Stuart Rogers
    Stuart Rogers Member Posts: 49
    tank

    Hi Tom,

    Sorry to take so long to reply -- it's been busy...

    The tank is slightly too small, not a huge problem. In the shoulder seasons when there's long periods between burner cycles and we're having to reheat all the supply pipes, the condensate doesn't make it back in time and make-up water gets added -- then the tank overflows during the cool-down. In cold weather with longer burn times/shorter cool-downs, the levels are more stable and less or no make-up water goes in or overflows.

    I'll see if we can adjust the float as you suggest. I don't think we can regulate the boiler level; it's controlled by a McDonnell Miller 150 float that I don't think is adjustable.

    The pressure (I'm delighted to say!) is 1.5 lbs in cold weather, and doesn't even reach 0.5 lbs in mild weather when our new outdoor reset keeps the burn cycle short. But the needle barely twitches off zero and the lady with the furthest rads says she is getting steam. (Last year, our 'handyman' had us running on limits only, at 7-9 lbs -- and as we learned during our rehab project this year, we had 60% failed traps (out of about 100). Should've had shares in the gas company stock.

    Stuart
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