1/3 hp submersibles exist?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by nc73, Sep 25, 2013.

  1. nc73

    nc73 New Member

    Messages:
    12
    Location:
    Aylett, Va
    So I was thinking possibility of going open loop in my geothermal and upgrade to closed loop later on. In order to reduce pumping costs I'd like to use a smaller pump. Do they make 1/3 hp submersibles any more? What about just buying the motor and putting it on a goulds pump end? I currently have a 3/4 hp pump. I thought Grundfos made one a while back. I only have to pump around 50ft to the surface.
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    Most companies that still make a 1/3 HP motor just stamp 1/3HP on a 1/2HP motor. However, it is the pump end that actually determines how much energy the motor draws. For instance Grundfos makes a 7S05-11 and a 7S05-8. Both are designated as ½ HP pumps. However the 8 stage used to be a model 7S03-8, which is only 1/3 HP.

    So you can still get 1/3HP pumps if you know how to figure the load, you will just have to put a ½HP motor on it since that is all you can find anymore. And really, all motors have been shortened up over the years to promote planned obsolescence, so the 1/2HP motor is probably even shorter than the old 1/3HP motors of the past when things were made to last.
  3. nc73

    nc73 New Member

    Messages:
    12
    Location:
    Aylett, Va
    So what brand is actually reliable nowadays? Seems everything is now made in China or Mexico. Maybe do an airlift pump and I'd only have to worry about the air compressor and jet pump at the top. No pulling pumps. Although wouldn't keep up with Geo even with a huge tank it'll run all day.
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    No air lift won't work or be efficient for the Geo heat pump system. Do you also use this well pump for house water? If so you can't go with too small a pump or you won't be able to take a shower. What is the GPM requirement of the heat pump?
  5. nc73

    nc73 New Member

    Messages:
    12
    Location:
    Aylett, Va
    I was going to boost it with a jet pump for home use. It takes about 1.5gpm per ton for open loop, so 4.5 total.
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    Now you are on the right track. I would use the 7S05-8 Grundfos pump with a 1/2 HP motor. If you can get a three wire motor with a (cap start, cap run) control box it will be slightly more efficient. Then all you need is a Cycle Stop Valve so the well pump doesn't cycle itself to death when using small amounts of water for the heat pump. See this link to a two pump system drawing.
    http://www.cyclestopvalves.com/csvapplications_8.html
  7. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    537
    Location:
    SE Texas-Coastal
    That's an interesting set-up Cary. Never seen one like that before.
  8. VAWellDriller

    VAWellDriller Member

    Messages:
    171
    Location:
    Richmond, VA
    I like that idea too....getting ready to build my own house and I just might do that exact system.
  9. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    Here is a better picture. Keeping the pressure as low as possible for the heat pump saves the most energy. Heat pumps don’t care if they get 20 PSI or 50 PSI. They only care about the flow rate. At low pressure a small submersible can supply enough flow or GPM for the heat pump and the house. Only when the house needs water, will the booster pump be running and boosting the 20 PSI to 50 PSI for showers, sprinklers, and other things for the house. Heat pumps run for long periods of time compared to the house needs. So the booster pump only runs 30 minutes or so per day, while the well pump and heat pump could be on for 18 to 24 hours a day.

    The CSV on the well allows the pump to supply as much or as little water as needed. Same for the booster pump to the house.
    [​IMG]
  10. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    537
    Location:
    SE Texas-Coastal
    So my friend is looking at doing an open loop Geo "pump and dump". He is planning on using one well for the house and Geo with the discharge water going to a pond for irrigation use. A 2nd well is not an option due to new rules.

    The unit will be a 4-ton unit. I am not sure but I believe that you need about 6-8 GPM per ton. This is in a cooling demand environment. The books say our water is 67-72° degrees year round. The well will make plenty of water. The quality will probably be in the medium range but should be free of sand and grit.

    I guesstimate the water level to be 60 -80 ft deep. Assuming the unit needs 8 GPM per ton that is about 32 GPM of water for the a/c. Assuming that the house needs about 10-15 GPM you end up needing a 40-50 GPM pump. With the water level that would take a 3-5 HP pump at pressure.

    I am trying to talk him out of it but might end up using something like this to make it work. Cary do you have a system like this at your place? I'd love to know the details. I have very little experience with Geo. There were a few pump and dumps here in the 80's but most have went back to an air source heat pump.
  11. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    I have helped several people install this two-pump method, which works very well. I have a similar system, but mine uses two wells instead of one well and a booster pump. I have a 1/3HP sub in a well that supplies the Geo system. Then if the house uses water there is another well with a 1/2HP sub that comes on to supply the added water needed.

    My 3 ton Geo system only requires 4 GPM flow. If your friends Geo really needs 6-8 GPM per ton, plus another 10 GPM for the house, that would take 42 GPM. Even just delivering 20 PSI to the Geo system, from a lift of 80’, that would take a 2HP sub. What “new rule” are you talking about that won’t allow the use of a 2HP? That would also be fairly expensive to use for pumping to a Geo system.

    You need to find out the exact GPM per ton that is needed, and do a pump test to see at what level the well will be when pumping this amount. If you can do this with 4 GPM per ton and the pumping level is 60’ instead of 80’, it would cut the pump size in half to a 1HP, which would also cut the pumping cost for the Geo in half.
    To be even more efficient, I also take the water needed for the house from the discharge side of the Geo unit. When cooling the water to the house is 10-15 degrees higher than well water temperature. This actually cuts down on the cost of producing hot water as it feed the water heater with 10 degree warmer water. And many times the cold water at 82-85 degrees is warm enough that no hot water is used during showers. If I want a cold shower I just have to turn off the AC unit before showering, but I don’t like cold showers. There is usually enough cool water in the lines to get a glass of cold water when needed. Other than that the toilets, sinks, washing machine, etc., don’t care if the water is a little warmer coming in.

    Taking the house water off the discharge side of the Geo system reduces the total demand by 10-15 GPM. So now if you can use 4 GPM per ton and take the house use off of the Geo, you only need a 16 GPM pump. At 80’ and 20 PSI that would only take a 3/4HP well pump. A CSV can take a ¾ HP load down to 1/2HP when using less water, now we have a system that use 25% of what a 2HP well pump would do.

    Of course you will need about a 3/4HP jet pump to boost the 20 PSI coming from the well pump to the Geo system up to 50-60 PSI for the house. But the jet pump will only run maybe 30 minutes a day to supply the house, while the little 3/4HP well pump might run 18 hours a day for the Geo unit. You still want to keep the well pump as small as possible, but this two-pump system can reduce the pumping cost for the Geo by more than 50%.
  12. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    537
    Location:
    SE Texas-Coastal
    Not a rule on a 2-HP pump, but a rule on how many wells we can have (GWD rule).

    He is trying to accomplish three things with one well: Fill a pond, run his house, and run his a/c. He will be filling the pond no matter what. He figures that by using the water he would normally use to simply fill his pond he will instead be recouping some of the energy to cool his house at a higher efficiency. When he does not use A/C he will open a bypass and fill the pond directly from the tank.

    I do not know the exact GPM per ton required. I had it in my head it was about 10 gpm per ton but I have no experience. What you're telling me is that for a 3-ton system you only need 4 GPM total? That number works out much better in his favor. Because he will still be filling his pond he will probably always use a 2-HP. I guessed at the water level because the well has not yet been drilled and I do not have any recent job experience close enough to reference.

    I think my 10 gpm per ton came from geo numbers used up north where they use 55 degree water for heating (hence the higher flow rate). We will be using 70 degree water for cooling.

    The well should have little to no drawdown as a properly constructed 4" well here will do 100 GPM easy. I'm more concerned with the quality of the water effect on the coils etc.

  13. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    If he is running a 2HP to fill a pond anyway, he just as well get the heat/cool off of it on the way. But a 2HP is not cheap to run 24/7.

    I do the same thing but only have a 1/3HP running 3 GPM to the pond. I have found that filling the pond and teeing off to the house after the heat pump coils keeps the coils clean. Even when the AC is not working there is still water going through the heat pump coils. This seems to wash away the hard water deposits in the coil. At least I haven't had to clean my heat exchanger coils in 8 years now, and I have very hard water.
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