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adjustable aquastat setting in conjunction with solar

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if i have water preheated by a solar loop.....which is then fed into the indirect cylinder attached to the boiler....what setting should i use for a variable aquastat on the indirect tank?

my intent is to have the boiler cycle, and make the water in the indirect reasonably hot, and then the incoming water is preheated by a separate solar system.
i would hope that the boiler would not cycle again until the water being fed into the indirect tank from the solar tank has cooled due to minimal solar gain.
so for example...if my boiler is set at 180... what should be the tank max temp, and the differential setting.

i think the aquastat has a max setting of 45 degrees differential. can i set the tank max at say 170, with a max differential of 45 degress, which would not recycle the boiler until it dips to 125??

hopefully im being reasonable

Comments

  • hot_rod
    hot_rod Member Posts: 22,157
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    the indirect tank aquastat

    should be set at the temperature you want at the DHW loads or faucets.

    It may be possible for the solar preheat to supply a temperature hotter then you might want. Depends on your panel and tank size. You might add a thermostatic mixing valve at the solar tank to limit it's output temperature to the indirect cylinder.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • phil the limey
    phil the limey Member Posts: 31
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    i put an anti scald mixer after the domestic tank, before any loads, thereby not cooling the solar before it enters the dhw tank.

    so what is a good temp for dhw? and where would y'all set the adjustable aquastat differential in this case?
  • hot_rod
    hot_rod Member Posts: 22,157
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    The correct temperature is

    depends on who you ask :) The water heater manufactures suggest 120F. and they include scald potential charts for temperatures above that.

    Dishwasher manufactures like 130 to dissolve soaps. Some say 140 to assure potential baterica is handled.

    Too cool and you have baterica issues, too warm and you risk soft tissue lawsuits. I doubt anyone will give you an "exact' number.

    I suppose ideally 140 into the system and a mixing device at EVERY hot water faucet and connection, would keep everyone happy.

    I noticed a few anti legionella devices at the ISH show this spring.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ted_5
    Ted_5 Member Posts: 272
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    do you have a

    transfer pump from the preheat tank to the indirect? How is the solar heating the preheat tank? Do you have a drawing? There are controls that can do this. If you did not want to spend the money a complete package, then you could do it with aqua stats. If you do not have a transfer pump then put an aqua stat in the preheat tank also. Set them both to your DHW temp. Run the boiler enable wires in series. This way both your preheat and DHW tank temps would have to be lower then your set point before your boiler kicks in. I would set the differential between 7 or 10 degrees.

    Ted
  • phil the limey
    phil the limey Member Posts: 31
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    i dont have a transfer pump. the dhw tank is positioned directly above the solar storage tank. basically a preheat of my domestic hot water, in an effort to save energy costs. i have attached a pic of the tank setup. the solar panels run through the indirect loop of the lower tank.

    the solar tank regularly gets up to 170 degrees.
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