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dual coil tanks

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radmix
radmix Member Posts: 194
in Solar
I installed a dual coil tank on my last solar project and I'm finding out that since the solar coil is on the bottom  and the boiler coil on top, when there is a call for DHW from the boiler there doesn't seem to  be allot of recovery rate from the tank. Because the boiler coil is the top coil it seems that only half of the tank is heated. Does anyone else have this problem.

Rich
lkstdl

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  • hot_rod
    hot_rod Member Posts: 22,143
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    how much boiler?

    and what type of DHW load?



    True that upper coil will only warm and store heated water at the top 1/2 of the tank. assuming it does not have a DHW recirc pump :) Typically a solar tank would be 65, 80, or 119 gallons, so you should have a fairly good amount of storage. But you need to supply what the house hold needs or expects.



    On my system I have a Lochinvar Knight 80,000 feeding the upper coil on priority. it is all piped with 1" and has a dedicated Grundfos 15-58 on speed 3. It has a tank, with a 1" stainless upper coil so it transfers the BTUs well. I can run the hot water non stop with a single faucet flow and never run out of hot water, even without any solar pre-heat.



    I'm on a well so my incoming water never drops below 50- 55F. Incoming water down in the 30's will of course change the load.



    For large DHW expectations a dual tank system is nicer. The first tank is just solar pre-heat, the second is sized for the load even without solar input.



    Here is the tank I have, without the two large windows :)



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Is_solar
    Is_solar Member Posts: 10
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    what brand?

    What make of tank is it.

    ive used heat flo and steibel eltron and never had that problem.  Maybe just turn up the upper limit on the upper coil.
  • radmix
    radmix Member Posts: 194
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    Dual Coil

    My boiler is a Triangle Tube 110, I have 2 dual coil solar 119 gallon tanks for space heating and pre heating DHW. I also have a 50 gallon dual coil tank for my DHW. My control strategy is to feed the 50 DHW tank with solar until  it reaches temp and then I'm using a 3 way diverter valve to route the solar to my space heating tanks. When there is no solar gain, I seem to have a lack of hot water. I believe I have to increase the capacity of my DHW tank.
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