Electrical demand for 1/2 hp pump is 1.4kw?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by tom.andersen, Oct 18, 2009.

  1. tom.andersen

    tom.andersen Software programmer

    Messages:
    3
    Location:
    Meaford, Ontario, Canada
    I just installed a whole house energy monitor, and was surprised by the fact that my 1/2 hp franklin well pump uses 1400 watts. I never thought that the well pump would use so much electricity. 1/2 hp is after all only 746/2 watts. I guess the 1/2 hp is the 'output hp' of the pump, and it is ~25% overall efficiency?

    It would not be a big deal, except that I am on an open loop geothermal system. I have read a few posts in here - great info - and I know that this is not ideal, but here is my system:

    80 ft well, water level is about 40 ft down, lots of water. Some calcium in it - but I don't think that that is an issue, as over 90% of the load on the GSW 036 heat pump is heating our heated floors. I think that mineral release only occurs if you heat water up. I take in water at 11 C and dump it at 4 C. This is about the minimum water that I can get the heat pump to work with, any less and the freezing protection will trip in the heat pump. I change the floor water temperature a few times through the heating season to maximize efficiency (90 - 105F). The drain for the heat pump just goes into a wet field via buried big - o. (so no possibility to benefit from siphon effect for geothermal drain).

    When the heat pump is operating, the well pump cycles at about 50% duty load, into a very large pressure tank here in the house. The water pressure is at 45 psi. The heat pump likely runs over 70% of the time from Nov 15 - Feb 15. I use my wood stove on cold nights, instead of letting backup kick in.

    So after reading some posts in here: I come to the conclusion that I can reduce my electrical demand by lowering the water pressure in the house (not gonna pass), or - what I think is perhaps a doable plan - lower the pressure in the large pressure tank to ~20 psi, then have a small pump drive the house plumbing off of the 20 psi system.

    1) Its bad for a pump to cycle. Mine runs for 5 min on then 5 min off. Perhaps this is OK? Its not cycling every 10 seconds. Its been cycling for 4 years now. (say 5 to 6 months/year like that)

    2) Is 1.4 kW really the amount of electricity for a 1/2 hp pump driving up 40ft then into a 45 psi tank?

    3) Are there any problems with having a separate pump in the house for domestic water? What is a really quiet dependable pump (two showers, 3 kids, not much lawn watering).

    In the summer, I cool by making cold water with the water to water heat pump, then drive the cold water up to 3 'multiaqua' heads in the highest places in the house. Works fine.

    I include a photo of energy use this morning - you can see the heat pump turn on 3 and half times, and the 1.4 kw well pump are the 3 ish bumps on top of each heat pump cycle. Its 5C outside, so its not running at full tilt today.

    Thanks for any thoughts.

    --Tom

    Attached Files:

    Last edited: Oct 18, 2009
  2. tom.andersen

    tom.andersen Software programmer

    Messages:
    3
    Location:
    Meaford, Ontario, Canada
    More info: The well is only 60 ft from the pressure tank, and its all 6 years old. Looks like 1.25 " plastic coming from the well to the house.
  3. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    1400 w

    http://books.google.com/books?id=DD...num=4#v=onepage&q="Table 430.248" NEC&f=false
    Table 430.258 says 1127 W, so this is a close call.
    This table might show 95th percentile values.
    At 5 A, 1 ohm worth of wire [500' of #10 two conductor] would take another 25 W.
    If your voltage is 10% higher than nameplate value, this would come out to ~1270 W.

    No other symptoms?
    Sounds like you should ask the manuf. if this means a failure is coming.
    Last edited: Oct 18, 2009
  4. tom.andersen

    tom.andersen Software programmer

    Messages:
    3
    Location:
    Meaford, Ontario, Canada
    Ok found the 1400 watts, its apparently correct.

    It works out to 1400 watts (6 amps at 230 - we are on 240) - exactly what my TRMS metering says. The CSCR control box is only about $120 and will pay back in one year or so for me. FRANKLIN Mfr. Model # 2824055015

    So if I want to save even more, I will lower the pressure on the well pump system to about 20 psi, then put in the booster for domestic. That will cost more, though, have not done the payback on it.


    This is a quote from:
    http://forum.geoexchange.org/viewtopic.php?f=2&t=14&p=167


    "
    Submersible Pump Motor, Capacitor-Start, Totally Enclosed Nonventilated, 1/2 HP, 3450 RPM, 230 Volts, 1 Phase, Service Factor 1.60, Full Load Amps 5.0/3.5, Max SF Amps 6.0/4.3, Thrust Rating 300 Lb, Number of Wires 3, Thermal Protection Auto, Mounting NEMA, Diameter 4 In, Control Box Required 1LZV8, Amps for CSIR/CSCR Control Boxes 6.0/4.3

    Note the S.F. amperage rating, 6.0/4.3. This confused me at first why there were two numbers. Long story short I ended up talking with a Franklin pump engineer. All of these pumps have a matching control box that is installed at the same time as the pump and they are a matched set. In the case of my pump they offer two types. One uses capacitor start, induction run, and the other capacitor start, capacitor run. The induction run control draws 6.0 amps, this is the one I have, and the capacitor run control box draws 4.0 amps, the one I want! I’ll be placing an order for the control that uses CSCR to replace my current CSIR box. According to the Franklin engineer there is no loss of pump performance changing to CSCR. Changing to the lower amperage controller will have a payback in less then a year in electricity usage.
    "
  5. upper

    upper DIY Senior Member

    Messages:
    154
    Location:
    Fresno, CA
    Matched set? Boy you need to talk to my first wife she was an engineer.......Upper she is drawing way more amps than that......................
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,464
    Location:
    Lubbock, Texas
    Reducing the pressure to 20 PSI won't lower the amp draw unless you also switch to a 1/3 HP pump.
  7. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    HP = GPMxHead/(40xEfficiency)
    Changing the head without anything else changing should affect the required HP, and so the current draw.
    Some pump curves show efficiency in addition to GPM and Head.
  8. valveman

    valveman Moderator Staff Member

    Messages:
    4,464
    Location:
    Lubbock, Texas
    Reducing the head will give you more flow, unless you reduce the horse power by slowing the pump or using fewer stages. With the same number of stages and spinning 3450 RPM, the only way to reduce the head is to increase the flow rate.

    Removing a few impellers to make the pump produce the lower head required, will decrease the horse power and the electric bill without reducing the RPM.
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