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Thread: 1/3 hp submersibles exist?

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    DIY Junior Member nc73's Avatar
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    Default 1/3 hp submersibles exist?

    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.

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    Moderator valveman's Avatar
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    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.

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    DIY Junior Member nc73's Avatar
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    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.

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    Moderator valveman's Avatar
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    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?

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    DIY Junior Member nc73's Avatar
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    Quote Originally Posted by valveman View Post
    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?
    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.

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    Moderator valveman's Avatar
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    Quote Originally Posted by nc73 View Post
    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.
    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

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    In the Trades Texas Wellman's Avatar
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    That's an interesting set-up Cary. Never seen one like that before.

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    DIY Senior Member VAWellDriller's Avatar
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    I like that idea too....getting ready to build my own house and I just might do that exact system.

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    Moderator valveman's Avatar
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    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.

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