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Thread: Grundfos UP 15-425F pump in solar drain-back system

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  1. #1
    DIY Junior Member glenb's Avatar
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    May 2012
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    Moultrie, GA
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    Default Grundfos UP 15-425F pump in solar drain-back system

    Hello,

    I have a Grundfos pump that I have not tried yet in my solar drain back system. I am wondering if this pump is self-priming
    (suction)?

    Along with this question, I have another question on where to locate the pump. If it is self-priming, it would seem to me that the
    pump should be located above the water level of the solar collection tank, to allow complete draining when off. Is this correct thinking?


    My system: two homemade solar collectors made from heavy aluminum flashing over pex-al-pex pipe, 80 square feet. Collectors angled at winter angle, because of possible overheating, permanently. Lexan covers and 1" polyiso insulation on the back.
    Insulated tank, 180 gallons, with 150 feet of 1" pex pipe in the water as a heat exchanger. Thermistors in tank, both collectors, and outside air. Homemade temperature controller with graphic screen.

    Tests have indicated that the BTU output of the collectors in series is over 15,000 BTU/hr in the early afternoon. Temporarily using
    cheap AC submersible pump from Lowes.

    My first PV system is also now installed, 2.6kw 12 Canadian solar CS5-230P, 3 BP 150W panels, Fronius IG-Plus 3.0-1. Producing
    14-15kw per day.

    First post!

    Take care,

    GlenB
    Moultrie, GA

  2. #2
    DIY Junior Member glenb's Avatar
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    May 2012
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    Moultrie, GA
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    Default

    Since I received no responses so far, I hooked up the pump and primed it. I put it below the tank water line to start, and water came out the discharge end without
    running the pump.

    I must not understand Grundfos model markings, because an explanation I saw on one of the web pages says the first number is the inlet size (15mm) and the second
    number is the amount of decimeters of head. Well, 145 decimeters is 14.5 meters. That is a lot of pressure. However, the pump could not even do 6 feet of head.
    A total waste of time! I saw the water make it out of the first collector, but did not make it to the second collector.

    GlenB

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