First forays into Series 7 - need pump advice

Discussion in 'General Discussions' started by engineer, Oct 12, 2014.

  1. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    New construction of custom homes has restarted in my area after a long hiatus and I'm suddenly looking at several S7 projects. All mine are open loop with reinjection, but are divided into two subcamps:

    1) Those with flowing wells - 6+ psig of static pressure at the well head

    2) Those with standing water 10-20 feet below ground level, mostly owing to a huge paper mill whose water usage depresses the aquifer.

    I want to design for lowest possible pumping power consistent with maintaining high efficiency of the S7s. I've done several dual Series 5 systems fed by a single well pump (submersible near the mill, surface elsewhere) with speed controlled via a Franklin Monodrive. I'd like to move away from that solution, at least for flowing wells, in favor of using the 0-10 VDC output to drive a variable speed Flow center.

    WaterFurnace has the 7-Bration rebate program going again, and that requires purchase of a flow center or modulating wellwater valve

    So I'm reaching out to you guys with S7 experience who are focused on keeping pump power to a bare minimum.
    Folzie75 likes this.
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We use variable speed well pumps (constant pressure) with the modulating wells which are regulated by the 0-10 volt signal. so the more the valve opens up, the well pump recognizes the pressure drop, and revs up. I just calibrated the sensors, so I measured some performance, the spreadsheet is attached. You are on the right track, the 7 series will have about 3 times the run time of a dual stage, so you have to pay attention to the circulation pump. My pumping power is anywhere between 10% and 38% of the whole system consumption, but I am rewarded with 56F all year around.

    The variable speed well pump serves 3 heat pumps in this example, but the principle is the same, we did many more as single HP setup pump with a smaller variable speed well pump.

    I have not found a better and more efficient way, the well pump draws a minimum of about 250 watts, and revs up to 1500 watts when all 3 heat pumps are running.

    Attached Files:

  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    For my flowing wells I think I can use a Flow center with (JUST!) the variable speed pump. Do you have any preference for Wilo vs Grundfos? It seems like a Ford / Chevy question...each has its ardent fans.

    What variable speed controller and well pump are you using? The Franklin doesn't like to go down to the pressures I need, but the interposing modulating well valve would let the Franklin run at a pressure more to its liking, albeit at some added energy cost.

    Thanks for the spreadsheet data...every system ought to be so monitored.

    Recently I had the dubious honor to have to service a shallow well open loop system - 5 ton compressor using 12 amps, 1.5 hp well pump using 10 amps!

    I think of myself as a one-eyed man in the land of the blind.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The concern I would have is how the circulators would like the biological stuff in the water. I use both, the grundfos is good with closed loops and single HP standard designs and comes with the full package from WF, but I use the Wilos when I need more flow or multiple heatpump application, where I need a constant pressure application.

    We are using Goulds variable speeds and their controller, never had any issue with them. I agree, sometimes the min pressure for the well pumps is counterproductive, since they waste some energy, there should be a variable pump designed for less head and more flow. We are clearly wasting some energy sometimes, but the heat extraction or rejection pays you every dime back when you get 55F all year long.....At WEL 762, we are using 251 watts when a single HP is in first stage, and are using 38% of total system system power consumption for pumping, but still are getting a total system COP close to 6, pretty much all year around. So I don't know if I am too critical here, especially since I have not found a better or more cost effective way.
    Last edited: Oct 12, 2014
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Extraction from 72*F is especially sweet...for the six or so weeks we need it.

    I'm envious of your deep ground temps, but not your winter weather.
  6. Folzie75

    Folzie75 New Member

    Curt, What have you found to be the best pump setup for situation #1? I too live in Florida and have positive pressure wells from the aquifer. Currently I have a 3 ton unit that discharges into a reinjection well and a 2 ton unit that just dumps into a small pond on the side of the yard. Currently, each unit has its own 1/2 hp jet pump that kick on when the unit kicks on. There are no pressure tanks. Only thing I have installed to the pumping system since buying the house are flow restrictors in an attempt to at least slightly increase the pumping efficiency. I'd like to get something more efficient, but it seems like most setups are either for closed loop, or traditional wells with submersible pumps, neither of which are ideal for this situation.


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