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Ambient Air DHW Preheat

I try to keep up on all things that save residential energy, but I haven't heard of this one yet:

With all this hot weather lately (95F avg. daytime highs) it occurred to me that a fan coil to preheat domestic hot water might have a quick payback. Heck my showers are only at about 106F, but the water coming in from the street is 55F. Are you thinking what I'm thinking?

Has anyone seen a device like this? It would be a lot cheaper and easier to install than conventional solar hot water.
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments

Comments

  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Drycoolers

    such as used for closed condenser water cooling systems may make sense, assuming you remember to drain them down come winter.

    On occasion I have used drycoolers (fan and coil like a condensing unit without the compressors) to make "free" hot water for summer reheat, to temper high ventilation spaces by diverting the normal flow up through the drycooler. Usually it is enough to do the job even if in the shade.

    I think you are on to something. Preheat at least, is essentially free...
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Drycooler

    Brad, thanks for giving it a name so I can do a little more research. For freezing climates, I envision it being inside, perhaps in a ventilated room.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • hr
    hr Member Posts: 6,106
    Yes

    I have lost the link but there is a company that makes DHW pre-heaters. Looks like a large Modine hydronic unit hesater with a drip pan below.

    It ventilates your attic and prehesats the water before the tank. It would need some sort of freeze protection mechanism, perhaps like a drain back tank system.

    I also heard of a steam back system Schuco is working on. It is an overhesat protection devise that allows the water to steam out of the glycol solution to prevent solar panel over hest. Takes a special glycol blend. I will try to get more details.

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  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    When I started....

    And boilers were big and furnaces were way oversized, I used to see lots of "pre heater tanks" in the basement.They held the water that would be going to the water heater in check, pre heating it in the space.

    They were usually 40 gallon galvanized tanks, set vertical on a stand. They had a swing check in the line to make sure that water only went to the heater when needed.

    Boy, I dont miss removing those things! Chris
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Chris

    Despite recent birthdays on your part :) you are NOT old enough to start telling, "back in the day" stories....Got it?

    You are starting to make me feel old... wait- I am getting there... slowly.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Uninsulated preheat tank

    That's one of the simplest ways to do it. In order to take advantage of Global Warming, one could then ventilate the mechanical room so it tracks outdoor temperature in the summer. In the winter, it would still work like in the olden days.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,226
    Those were called...

    ...tempering tanks and used to be recommended by electric utilities in the early days of selling electric water heaters. Originally electric heaters had only .75 to 2 kw heating ability. They were slow to heat, so preheating the water made them easier to live with.

    Put your tempering tank in a hot attic and you've got solar preheat, (or night time cooling). ;~)

    Yours, Larry
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