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Thread: Thermosiphon System Design

  1. #1
    DIY Junior Member Quantumstate's Avatar
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    Default Thermosiphon System Design

    Just bought an imported thermosiphon evac tube system which I'm going to install on my house. 40 gallon tank at the top, with 24 evac tubes coming down. I want to connect this to my 38 gallon hot water tank.

    The solar heater is a no-pressure system, so I'll need a heat exchanger, and have in mind the Brazed Plate type, but no idea how to size it.

    Water will need to be forced through both circuits, so I have in mind a Liang DC pump on a solar panel for low pressure. OTOH I'll probably need hot water at night, so maybe this isn't such a good idea.

    I guess the heat exchanger would need to be on the roof, as I doubt the Liang could force water up one story to the roof. I'd rather not send domestic water all the way up there though, if I can avoid it.

    On the high-pressure circuit I have in mind teeing off the cold of the domestic hot water heater to go to the heat exchanger, and from there teeing into the hot side of the hot water heater. So water would circulate through the heat exchanger and hot water heater. I guess the pumps would need to be controlled by a differential thermostat, so the solar supplement is only on when it's warmer. Suggestions on brand for a thermostat, particularly one that has a network interface and computer software? (hopefully open source)

    Does my design seem sound?

  2. #2
    In the Trades Tom Sawyer's Avatar
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    Default

    the easier route would be to buy the exchanger, tank, pumps and controls as a package. Try these guys www.caleffi.com

  3. #3
    DIYer, not in the trades LLigetfa's Avatar
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    Default

    Quote Originally Posted by Quantumstate View Post
    I guess the heat exchanger would need to be on the roof, as I doubt the Liang could force water up one story to the roof.
    The weight of the hot water coming back down will almost balance it out so there would not be any heavy lifting. See "Density of liquid water" table in this wiki.

    http://en.wikipedia.org/wiki/Properties_of_water

  4. #4
    DIY Junior Member Quantumstate's Avatar
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    Default

    So my overall plan looks solid?

    Any idea how to size a Brazed Plate heat exchanger?

    This collector seems very efficient. What if the water gets up to 200 degrees, will it damage the hot water heater? I notice the T&P is set for 180, and would probably blow. Anyone had a problem with this?

    Should I run the domestic water up to the roof, or the low-pressure solar water down to the house? IOW, where should the heat exchanger go?

    Suggestions on brand for a thermostat, particularly one that has a network interface and computer software? (hopefully open source)

  5. #5
    DIY Junior Member cssolar's Avatar
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    Default non pressure swh

    Hi I have a non pressure vac tube swh on my house, I use the hot water direct, I have an auto boost pump to give pressure when I open a tap.

    If you want mains pressure I recomend a pre heat type swh, the water in the tank and tubes is non pressure but there is a copper coil heat exchanger in the tank that gives indirect mains pressure.

    how do you controll filling of your non pressure tank, assistant tank, electonic controll or manual fill ?

    Tony cssolar

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