Oil boiler storage tank and DSH connections

Discussion in 'Open Loop' started by clockwalk, Dec 20, 2010.

  1. clockwalk

    clockwalk New Member

    How should I connect the storage tank from my oil boiler to the SDH ? My storage tank has a "hot water out" connection at the top, a drain connection at the bottom, and two more water connections at the bottom. One is connected to the boiler and receives hot water from the boiler and the other goes back to the boiler. The tank does not have a heating element. It is an insulated storage tank.
    Thank you, ED
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    DSH needs its own tank with no other source of heat to work properly.

    There is a marginal way to plumb a DSH to a 2-element electric water heater which results in very limited recovery.

    DSH should not be connected to a gas fired water heater. I imagine it would be similarly useless connected to an indirectly heated water storage tank, which, if I've interpreted your post correctly, is what you have.
  3. clockwalk

    clockwalk New Member

    Curt, I have a storage tank that is connected to my oil boiler but the thermostat is shut off. I do not heat hot water from the boiler any more. i am looking for advice on the connections from the DSH to this storage tank. Please see my first post for a description of the available connections.I want to store water from the DSH in this tank and have it flow to the electric tank for final heating. I expect the storage tank will basically pre heat the water and the electric tank will raise the water to final temp for DHW. Just looking for advice on the connections .
    I have the boiler still connected because I plan on using it when we loose power. Don;t know if there are complications in the plumbing and thought someone may have done this before. Please note that I am not proposing to connect the DSH to the boiler.

    Thanks again, Ed
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    That makes more sense

    The two boiler connections at the bottom likely feed a coil within the tank that is isolated from the tank contents. They will not figure into use as a DSH.

    Does the tank have a cold water inlet that you haven't mentioned? That would be the place to plumb the DSH inlet. The DSH outlet, water coming back from the DSH, would be plumbed into the tank drain outlet. Ideally the cold water inlet has a dip tube that extends most of the way to the bottom of the tank.

    The hot water outlet gets plumbed to the downstream electric finishing water heater. As water loops from the CW dip to the drain it gets warm and when it is warm enough it rises up out of the circulation area to an undisturbed or stratified area near the top of the tank, awaiting demand by the downstream heater.
  5. clockwalk

    clockwalk New Member

    The drain on my storage tank is teed to the cold waterinlet. I don't have a cold water in at the top of the tank so it looks like I can't use this storage tank . Is a storage tank worth the investment as a pre heating tank before the electric tank?
    Thanks again,
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Oh yes

    Turning the question on its head - the added cost of a DSH will NOT be recovered in water heating savings UNLESS it has a dedicated, unpowered, unfired buffer tank. You've invested quite a bit in the DSH option. It would be a foolish economy to skip the buffer.

    I won't even discuss a DSH install without one.

    There might be a way to jury-rig your present tank. A concentric withdrawal / injection connection could be placed in the boiler drain if it leads straight into the tank without obstruction.This approach has sediment concerns. One might also breach the indirect coil line so that it connects with the contents of the tank.

    Another option - sell what you have and buy a moderate priced electric storage water heater. It has been awhile, but last I checked, indirect tanks were astonishingly expensive - what you have may be worth more used than the cost of a nice new foam-insulated 12 year warranty electric storage water heater.
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I emphasize buffer tank sediment much less in design. Our experience is such that there seems to be much less in unfired tanks and that channeling appears to occur where flow is routine (IOWs you'll have a clean path to a bottom outlet of the tank with crud on either side).
    Sound like an Amtrol tank which has cold water feed in the bottom and hot water out the middle top.
    I would go ahead and T DSH inlet to Cold line and outlet to hot line.
    I wouldn't encourage replacement untill needed. You could use boiler connections as well though there would be poorer performance.
    Good luck,
  8. clockwalk

    clockwalk New Member

    Joe, Yes , I have an Amtrol tank as you guessed. If I understand you then your suggestion is to tee the cold water and hot water pipes . The tee at the cold water inlet which is at the bottom drain of my Amtrol you would connect to the DSH in and then you would connect the DSH out to the tee at the hot water out of the Amtrol but isn't the idea of a DSH to raise the storage tank temp 5 to 10 degrees each time the water is circulated back to the DSH? Shoudn't I be taking hot water from the hot water out of the Amtrol tank and sending it back to the DSH in for reheating? Maybe this is what you are saying and I misunderstand.
  9. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I like to flow counter to the norm as warmest water would presumably be at the tank of the amtrol. One could also use a coaxial T.

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