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Thread: Water Source Heat Pump Deep Pump Sizing

  1. #16
    Moderator valveman's Avatar
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    Sammy, those Sub Drives and Mono Drives use a little go/no go switch instead of a pressure transducer. So they can never lock in on any one speed. They just continually ramp up and down to produce the varied amount of water being used. Put your amp meter on an incoming power leg and you will see it bounce up and down about 45 times per minute. You are right that it probably would not have caused a hole in the pump or motor housing if the pump had been hung straight. However, the motor torqing 45 times a minute witch is a million times every 21 days, will still probably wear out the wire down hole in short order. I hear of lots of people pulling these out after 6 months or a year and saying that the wire looked 20 years old.

  2. #17
    Previous member sammyhydro11's Avatar
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    yeah the guy was happy with the work. I was told that double jacket wire was the way to go but once i told him the price and how long it would take to get it the guy said no way. So i used the braided wire,wire guides every 30',and taped the wire every 7'. I hope it holds up.

    SAM

  3. #18

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    Just a few foolish observations - if the well is 500' deep why not put the water back into the well? Seems like enough earth to absorb the temperature change.

    I tape every 5 feet and use standoffs every 25 feet on all wells. Must be why they last so long.....

  4. #19
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by bravo454
    The reason for 1.5 gal/min versus the 2.5 gal/min open versus closed system is that the open systeem is using the water only once and will stay at a constant temp throughout the year. The closed system due to the thermodymnamic properties of the earth and the tubing used to bury in the ground, the fluid temp will drop in the summer and rise in the winter as the demand for cool/heat continues for long periods of time. The flow rates need to comensate for these temp changes in the closed system.
    In the summer, the AC is taking heat from the house and putting it into the water, raising the temperature of the water. If the water is pumped back into the well, then the temperature will slowly RISE in the summer.

    In the winter, the heat pump is taking energy from the water, causing the water to be cooled, and discharging it to the house. If the water is put back into the well, then it will cause the temperature of the well supply to drop.

    The most effective way to circulate the water to the ground is to inject it into the aquifer at some distance from where it was withdrawn from the aquifer. It then tends to flow through the aquifer from the injection point to the withdrawal point at the well.

    If the water level in the well is much below the surface the systems use a lot of electricity you usually don't recover all of the available head when the water is reinjected.

  5. #20
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    The problems with injecting back into the well is the oxidation of iron and other minerals that tend to plug the well up in short order. Especially screened wells.

    I have been around GWHP's since I was a kid, owned one that came with the house. I still don't see why anyone would want one.

    bob...

  6. #21
    In the Trades Bob NH's Avatar
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    If I had a good gravel aquifer with water at 25 ft below the surface, with enough space to reinject the water about 100 ft away, I would use it. If you have that kind of water source, you can extract or add heat with minimum pumping power. The water would not be exposed to air so it would should not increase precipitation of iron.

  7. #22
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    I suppose if it's done right, the water wouldn't have to see any air. I've seen the pipe going into a well seal then running the rest of the way down the casing through a column of air. With iron in the water you can imagine what the inside of that casing looked like.

    bob...

  8. #23
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    The problem arises when the return line is just stuck through the top of a well seal with no droppipe into the water below. This allows for a lot of oxidation and a real nasty looking casing in a short time.

    bob...

  9. #24
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by speedbump
    I suppose if it's done right, the water wouldn't have to see any air. I've seen the pipe going into a well seal then running the rest of the way down the casing through a column of air. With iron in the water you can imagine what the inside of that casing looked like.

    The problem arises when the return line is just stuck through the top of a well seal with no droppipe into the water below. This allows for a lot of oxidation and a real nasty looking casing in a short time.
    bob...
    Someone can always find a way screw it up, but with the vast amount of information available on the internet, the knowledge is available to do it right.

    http://www.energystar.gov/index.cfm?...geo_heat_pumps
    http://www.geoexchange.org/
    http://www.geoexchange.org/publications/maryland.htm

  10. #25
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    In your opinion Bob, do you think the GWHP's (ground water heat pumps is how I remember them) are actually worth the extra money and maintenance required? I had one not too many years ago and didn't see any savings whatsoever. The only reason I didn't change it out to air/air was the fact I was in the pump business and could keep it working cheaper than the average homeowner.

    Do you think they save that much in electricity in heating and cooling?

    bob...

  11. #26
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by speedbump
    In your opinion Bob, do you think the GWHP's (ground water heat pumps is how I remember them) are actually worth the extra money and maintenance required? I had one not too many years ago and didn't see any savings whatsoever. The only reason I didn't change it out to air/air was the fact I was in the pump business and could keep it working cheaper than the average homeowner.

    Do you think they save that much in electricity in heating and cooling?

    bob...
    Air-to-air heat pumps don't work well when the air gets down near freezing. Water to air heat pumps work well for heating if the incoming water is above about 45 F (warmer is better), and they work well for cooling if the water is a few degrees less than ambient air.

    Ground water heat pumps have a coefficient of performance greater than 3 (see first link in my previous post). That means that you get more than 3 kiloWatts of heat effect from one kiloWatt of power. That is a big saving if you are using electric heat. With fuel prices going up, it approaches the cost of gas or fuel oil in some areas.

    It will become even more important when we implement a coordinated energy and environmental policy that includes building more nuclear power plants to reduce both oil imports and production of greenhouse gasses. Also, the can't export many nuclear power plant construction jobs to China.

    In cooling applications the ground water systems have energy efficiency ratios (EER) in the range of 14 to 16 BTUs per watt-hour, which corresponds to a coefficient of performance of about 4.1 to 4.7.

  12. #27
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    Here; everything is electric and gas and very little gas. This keeps the electric costs less than they would be in the north.

    I am just curious with all the maintenance required with the well, pump, solonoid valve, return water (depending on where it is discharged) etc. Is it really that much of a savings. And the added initial expense for the installation.

    bob...

  13. #28
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by speedbump
    Here; everything is electric and gas and very little gas. This keeps the electric costs less than they would be in the north.

    I am just curious with all the maintenance required with the well, pump, solonoid valve, return water (depending on where it is discharged) etc. Is it really that much of a savings. And the added initial expense for the installation.

    bob...
    If I had a good source of ground water as I described earlier, my design for the ground water source would be as follows:

    The source pump would be a low-head submersible in a well in a shallow aquifer where the static water level is not more than about 30 ft down. The return pipe would be into the same aquifer around 100 ft away (that is just a guess without calculation), and the pipe would be submerged in the aquifer. That would keep the pressure at the top of the return pipe above zero psi absolute and would allow recovery of the elevation head. The energy cost would be the inefficiency of the pump, the losses in the pipe and heat exchanger, and the inlet and discharge losses in the source and injection wells. The pipes would be large enough to keep the pipe losses small.

    The pump would be matched to the heat exchanger requirements and there would be no flow control. The pump is on or off depending on demand.

    At an energyefficiency ratio of 14 for cooling, a 5 ton (60,000 BTU/hr) unit would require about 4.3 kW, or about 15,000 BTU of electrical power, so the heat exchanger would have to remove 75,000 BTUs per hour.

    At a temperature difference of 10 degrees F, it would require 7500 # per hour of water, or about 15 GPM. If you take 40 ft of head loss through the water system, that is 300,000 ft-# per hour or 0.1515 HP or 0.113 kW. With a pump at a wire-to-water efficiency of 40 percent, the pumping power is 0.283 kW.

    Add another .283 kW for each additional 40 ft to water. For that condition, skip the injection well unless it is necessary to recover the water.

    That number tells you how much is saved by the return well. If there is enough supply so the water can be wasted without reinjecting it, then maybe 20 ft of head is recoverable with the injection well. The additional pumping power to discharge it at ground level would be about 0.14 kW. If the water can be wasted and the cost of the return well (probably just a 2" pipe driven into the aquifer) is more than about $1000, it is probably not worth it.

    The advantage of groundwater cooling for A/C is that you are operating at far lower temperatures in the condenser, and therefore, with much less power for the compressor.

    The economics of the system would have to be calculated. I suspect that for the large multi-million dollar places that I see reported in Florida, a ground water source would be economical. I don't think it will be economical for a 1200 square foot place that uses one condensing unit.

  14. #29
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    That was the answer I suspected.

    In the million dollar + homes that are being built here, the other problem would be the water itself. We have requirements that are constantly changing. 25 years ago if you had a GWHP, you could discharge the water through sprinklers anytime of day or night any day of the week. Everyone else had water restrictions. Now, (last I checked) you have to reinject it into the aquifer. And you will do everything their way and that means more permits etc. etc.

    Of course if these folks in the million dollar + homes are worried about their heating and cooling, they should be far more concerned about their taxes and rising insurance costs. That's what's killing everyone.

    bob...

  15. #30

    Default Geothermal HP and well questions...

    I have just had fitted a 5 ton (two stage) heat pump with open loop.
    The spec sheet for the heat pump says 7 gpm on stage 1, and 14 gpm on stage 2. Stage 1 is about 3 tons, stage 2 is another 2 tons.
    The water supply will be two stage (tomorrow) by fitting a second valve for stage 2 demand from the heat pump.

    The well driller said that the well is capable of much more, so I presume that there is minimal draw down.
    The source well is 56 ft deep and the motor is sat in plenty of water (about 20ft I think).
    The discharge well is 70 feet away from the source, with about 50 ft of pipe between each well and the heat pump.
    I have a large rubber bladder tank in the water circuit.

    I have a few questions about optimal operation (my aim is to conserve energy).

    The well motor is 3/4 HP variable speed with a Franklin Monodrive. The pump and motor appear capable of more than the 14 gpm required for heat pump. Most of the time I only use stage 1 of heat. At 14 gpm a current clamp on the input of the mono drive shows a steady 5.2A (1.25KW power factor is 1.0). If I reduce the flow to 7 gpm the current flow drops to about 2.8A (varies between 2.6 and 3.2A or 0.67KW). If I reduce the flow to 6 gpm or lower the pump cycles off for a second or two each minute (bad).

    1) I am a little bothered that the pump motor has been over sized an I could have used a 1/2 HP or even 1/3 HP motor. Any comment?

    2) Are the heat pump manufactures (Flordia Heat Pump) asking for too much gpm? (Higher gpm makes their COP value look better, but wastes KWh on the well pump)

    3) Would a 1/2 HP or even 1/3 HP variable speed motor use much less KW? A smaller motor would work closer to its upper limit more of the time which is typically more efficient, or is the difference marginal?

    4) I saw a post that the Franklin Mono Drives ramp the speed of the motor up and down. What's the alternative? I'm already unhappy with the Franklin Mono Drive because it consumes 40W constantly on standby (energy efficiency is my aim). It is probably too late to do much now, but I'd like to hear the alternatives.

    5) I would like to conditionally switch the Franklin Mono Drive on when the heat pump or irrigation system call for water. The aim is to avoid the 40W standby loss of the Mono Drive. I could do this via a relay powered from the fan control of the heat pump and the pump control of the irrigation system. Any comments?

    6) I'm planning on connecting the irrigation system to the well. My plan is to use only the one pump. Local permits are not a problem. The question is should I connect on the supply side or the discharge side of the heat pump?

    If I connect the irrigation on the supply side, then the well pump will likely be able to provide for the heat pump on stage 1 and irrigation together, and then the irrigation can work independantly of the heat pump. For stage 2 (which is rare) the heat pump may be short changed, but demand from stage 2 would be hyper rare at the same time as irrigation.

    If I connect on the discharge side of the heat pump, then the heat pump will always have enough flow for both stages but then I either need to have the heat pump on to operate the irrigation or have the irrigation system open the heat pump's supply valve. Also unless I shut off the pipe to the discharge well with another valve the pressure seen by the irrigation system would be lessened.

    thanks
    Mark
    Last edited by mbartosik; 01-18-2007 at 03:48 PM.

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