Open-Loop Heat Pump - Power Efficiency

Discussion in 'HVAC Heating & Cooling' started by sixlashes, Aug 6, 2008.

  1. sixlashes

    sixlashes Plumber in Previous Life

    Messages:
    83
    Location:
    Pensacola. FL
    I have gone through numerous previous posts and cannot find the answer to this. Please forgive me if I overlooked it.

    QUESTION: How much power will a 1/3 hp or a 1/2 hp submerged well pump running at 70% capacity use? I cannot apply the figures I get from Grundfos/Franklin Motors/F&W for my situation. I am confident from reading previous posts that there are folks in this forum that are well versed in this.

    BACKGROUND: I am building my home and plan to install a Climatemaster Model 049 - 4 ton geothermal heat pump. I am trying to determine which pump (open or closed loop) will be more economical for the heat sink since the water temperature and power consumption of the chosen pump clearly impacts the overall system EER/COP.

    I have an abundance of good water at a depth of 50-55 feet here in NW Florida at year-round water temp of 68-69 degrees. If I utilize a horizontal loop 6' deep, my water temp will vary from the well water temp by approx 10 degrees. This does not take into account ground heat saturation during the long summer cooling load here in Florida which will further lower the efficiency of the closed loop. Will the increased EER/COP values at the more attractive well water temps be worth the added power consumption of the well?

    Since I am already installing an irrigation well, the cost of installing an additional well for the water source is more competitive than installing a ground loop. I plan to use the irrigation well as the injection well to minimize the possibility of fouling the screens with the small amount of iron present (assuming air gets into system). I have been told by drillers in the area that pulling large amounts of water at a high rate of flow back out of the injection well should eliminate\reduce clogging of the injection well screens.

    I am leaning toward the open system, but do not want the cost of running a well pump to make it more expensive. I am convinced we are on the precipice of vastly increasing utility costs and plan to live in this house for the rest of my life. What sayest thou?
  2. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    You left out the most important factor.

    You need to know what the water level is while the pump is running. This is generally not too much higher than the "static water depth".

    The total well depth is not important as long as it can supply the water at the required rate without the water level dropping too far.
  3. sixlashes

    sixlashes Plumber in Previous Life

    Messages:
    83
    Location:
    Pensacola. FL
    The static water level is approx 45 feet. The drawdown at 12 gpm should be no more than 10 feet. A knowledgable neighbor told me his is no more than 10 feet for his lawn irrigation pump.
  4. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    So you are lifting the water ~50 feet.

    1. Calculate amount of water per minute.
    GPM =

    2. Convert that to pounds.
    Pounds = GPM * "Pounds per gallon"

    3. Calculate the "Ideal" HP you would be using
    HP = (Pounds / 33,000) * feet

    4. double? it to make up for inefficiency of the pump

    5. Convert HP to watts
    watts = Hp * 745

    6. multiply by the amount of time it will be running. 70%?

    7. Multiply it to get Kwh per month
    kWh = Watts * 24(hours) * 31(days) / 1000

    8. multiply kWh by your price per kWh


    Anyone have there calculator handy?
  5. sixlashes

    sixlashes Plumber in Previous Life

    Messages:
    83
    Location:
    Pensacola. FL
    Great info. I think I have my brain wrapped around this.

    One last question - Ideally, I want a 1/3 hp pump because of the low head. I cannot find a decent brand in a third horse. They have been discontinued. I am forced to buy a 1/2 horse, either Grundfos, Gould or F & W. Will the 1/2 hp pump use much more power than the 1/3 hp doing the same amount of work?

    Okay, I lied. :D Second question comes to mind - In your opinion, which of the three is the best to go with, and are any to be avoided?

    Thank you for sharing your experience.
  6. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    >Okay, I lied. Second question comes to mind - In your opinion, which of the three is the best to go with, and are any to be avoided?

    In my opinion, you should run open loop first and use the savings to put in a more efficient drilled closed loop system. This is what I am planing.

    The costs of "caseless" vertical wells should come down as drillers get used to drilling only until it gets difficult.

    Drillers also need to change there rigs so that they can quickly change the angle they drill at so that you can drill at an angle to cover more area while reducing the size of the trench where the pipes are connected.

    I've been thinking of building a rig that can drill 50 feet using 1-1/4 pipe and then pushing a pair of 1/2 pipe down each well before filling it with sand and pulling the 1-1/4 pipe back out.

    Edit: oh. I think you are asking about which brand of pump to get, not which option to go with.
    Last edited: Aug 8, 2008
  7. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The Goulds 10GS05R is the best match in the Goulds line.

    I would use a variable frequency drive on the 10GS05R pump. To match your system it would run a little slower than the standard 60 Hz. There are several brands.
    http://www.hitachi.us/supportingdocs/forbus/inverters/Support/SM-E256P_X200.pdf

    The price for one at the link is less than $150 and a 3-phase motor is often less expensive than a single phase motor.
    http://www.driveswarehouse.com/c-149-drives.aspx?categories_id=21

    http://www.wwpp.us/goulds/goulds-submersible-2-wire.shtml

    You could dial in the speed (not an active control) to match the pump to your needs, but you could use it as a control if you had reason to do so.

    The ability to set the speed lets you adjust for differences in head losses in the system, and you could use it to optimize the pump/compressor power.

    Inverter-rated 3-phase motors are common.
    Last edited: Aug 8, 2008
  8. sixlashes

    sixlashes Plumber in Previous Life

    Messages:
    83
    Location:
    Pensacola. FL
    Bob NH,

    Will using the inverter give me the same problems as the constant pressure pump systems that seem to have a bad rap in this forum?

    Thanks.
  9. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The VFD for your system isn't applied in the manner that is used for constant-pressure systems described on this board.

    Most of the problems arise out of trying to make inexpensive constant-pressure control systems with inexpensive pressure transducers or pressure switches. The systems tend to cycle and hunt while they respond to varying demands of the system. You don't have that kind of system.

    The inverter will not involve varying control, pressure transducers, or cycling the pump on and off to meet varying demand. It will simply convert the 240 VAC single phase input power at 60 Hz to 240 Volt 3-phase power to a frequency somewhere between 50 and 60 Hz to provide the pressure you need for the heat exchanger. You will dial the speed/pressure/flow that you need and leave it there.

    Because the pump delivers more pressure and flow than you need you will never need to operate it above the rated speed, so you can use a standard pump with a VFD rated 3-phase motor of the specified horsepower. I know that Goulds sells pumps with such motors.

    VFDs are used in many applications where saving energy is an important part of the control system. They are used because they save energy. There is some conversion loss but the net effect is to save energy. There is not standby loss because the VFD will not be powered when the system is off.

    If you can match the pump to the system without a VFD that is the most efficient way to go.

    If your system can accept higher flow then the extra pumping power will probably be balanced by reduced compressor power.

    If you have to throttle the pump significantly then you can save energy with a VFD.
Similar Threads: Open-Loop Heat
Forum Title Date
HVAC Heating & Cooling best electric heat source for chalet home? Tuesday at 4:28 AM
HVAC Heating & Cooling Floor joist radiant heat system Jul 13, 2014
HVAC Heating & Cooling What size heating strips Jun 13, 2014
HVAC Heating & Cooling Help! Exchanger on Pool Heat Pump Leaking! Mar 8, 2014
HVAC Heating & Cooling Electrical question fir 5 ton pool heater heat pump Feb 28, 2014

Share This Page