high temp flow reducer in solar loop

Discussion in 'Solar and Geothermal Water Heating Forum' started by RoDa, Jul 9, 2009.

  1. RoDa

    RoDa New Member

    Messages:
    3
    I'm circulating water to my solar collectors with a 3 speed grundflos pump, but even on the lowest setting, the flow rate is too high - probably about 6 gpm when I need about 2, so the water never gets up to a high enough temp in the array.

    I could try throttling the rate with a ball valve that's in the system, but that's not a great solution, or putting in a 2 gpm flow reducer. However, all the flow reducers that I've seen have max temp ratings of about 70 C.

    Can anyone point me to a source for a high temp flow reducer, or suggest another alternative?

    thanks
  2. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    Why do you have to reach a set temperature?

    Unless you are doing thermal storage you won't get any more heat out of the panels by lowering the flow rate. In fact you get less heat as the water gets hotter.
  3. RoDa

    RoDa New Member

    Messages:
    3
    The heat gets transferred to a 100 gal hot water storage tank via an internal heat exchanger. Heat is transferred with greater efficiency at higher temp differences. So, if the water coming out of the solar array is as hot as possible, the heat will be more easily transferred to the storage tank for use in the rest of the house. Also, the circulation pumps are only start pumping when the temp difference is at least 12 degrees between the tank and the array, so if the water gets hotter in the array, there's less chance of short cycling.
  4. Alphacarina

    Alphacarina New Member

    Messages:
    26
    Location:
    Biloxi, MS
    My 4 by 10 foot AET collector panel specifies a flow rate of 1 to 1.5 GPM. I use a 2 GPM pump and a ball valve and adjust it to about 1 1/4 GPM

    I'd suggest you go with a smaller pump and a ball valve to make adjustments - You'll need a flow rate meter of course

    Don
  5. flamefix

    flamefix New Member

    Messages:
    71
    Location:
    Exeter, England
    Why be afraid to flow restrict with a ball valve? sure you'll get some cavitation around the valve but it will not cause significant problems.

    Perhaps look at the pump controller arrangement you are using and have a controller and pump that can be speed regulated within the pump speed settings on the physical pump. Typically the systems I use can regulate the pump for a set percentage of its maximum speed (set by the pump speed selector).
    Check this for info it can control pump speed and there are many others. http://www.resol.de/Produktdokumente/48000500_DeltaSol_BS_Plus.monen.pdf
  6. protech

    protech Master plumber

    Messages:
    53
    Location:
    Central Fl
    You can also use the capillary tube concept. Make several loops of pipe that is a smaller size than the rest of the loop piping to increase the amount of "friction head" that the pump experiences. Be careful though, you must not make the loop to short or two small or the velocities in the loop will be too high and cause rapid pipe wall erosion due to cavitation damage. Check your flow rates and convert gpm to fps to confirm that you aren't going over 5 fps in your capillary tube. If done right, this method of throttling will last as long as the rest of the system without the need for service.

    This is what a capillary tube looks like:

    Attached Files:

  7. protech

    protech Master plumber

    Messages:
    53
    Location:
    Central Fl
    You know that there is no harm in going higher for your type of system right?

    Open loop aka direct systems do not need to have slow flow rates like indirect systems do. If you have a 3 dip tube tank with a baffled return dip tube, stratification will still occur at higher flow rates.
    My AC power taco pump moves 4gpm and my tank stratifies perfectly. Your lower output DC powered pump can run wide open and still dot disturb your thermocline layers.

    Just thought you should know that ;)

    Last edited: Sep 14, 2009
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