Selecting the right pump (1/2 or 3/4 HP) 2 wire or 3 wire

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Valveman

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I have always known that the design of the Grundfos impeller stack has a much better drop in horsepower than most other brands of pumps. The new software that Grundfos has for sizing pumps is excellent. (seen here http://product-selection.grundfos.com/catalogue.html)

I have wanted to see the horsepower requirements for these small pumps for years. This information has always been available for larger pumps, just not the small ones. Many of Goulds larger pumps have a good drop in horsepower, but not all of them. However, the design of their small plastic pumps doesn’t allow the impellers to unload as easily as the fixed stack design with the Stainless Steel impellers of the small Grundfos pumps.

Actually Grundfos pumps are so good at reducing the amp draw when simply restricting the pump with a valve, that it is almost impossible to beat it even when using a Variable Speed Drive. The 3” SQ pumps don’t have nearly as good a drop in horsepower as the 4” S series pumps.

With the new software I haven’t figured out how to show the horsepower when using the CU301 box to make the SQ a variable speed design. But my guess is that it will not be much different from what their 4” pumps will do naturally by just restricting the flow with a valve. This maybe the reason this kind of information has not been available before, because it shows the natural drop in horsepower to be about the same as could be done with a variable speed drive attached.

I have always known that if this kind of information were available, people would realize VFD’s do not save energy on these kinds of systems. I am going to make some copies of all these pump curves, because once Grundfos realizes what we can do with this information, it maybe quickly taken off line.
 

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I have always known that the design of the Grundfos impeller stack has a much better drop in horsepower than most other brands of pumps. The new software that Grundfos has for sizing pumps is excellent. (seen here http://product-selection.grundfos.com/catalogue.html)

I have wanted to see the horsepower requirements for these small pumps for years. This information has always been available for larger pumps, just not the small ones. Many of Goulds larger pumps have a good drop in horsepower, but not all of them. However, the design of their small plastic pumps doesn’t allow the impellers to unload as easily as the fixed stack design with the Stainless Steel impellers of the small Grundfos pumps.

Actually Grundfos pumps are so good at reducing the amp draw when simply restricting the pump with a valve, that it is almost impossible to beat it even when using a Variable Speed Drive. The 3” SQ pumps don’t have nearly as good a drop in horsepower as the 4” S series pumps.

With the new software I haven’t figured out how to show the horsepower when using the CU301 box to make the SQ a variable speed design. But my guess is that it will not be much different from what their 4” pumps will do naturally by just restricting the flow with a valve. This maybe the reason this kind of information has not been available before, because it shows the natural drop in horsepower to be about the same as could be done with a variable speed drive attached.

I have always known that if this kind of information were available, people would realize VFD’s do not save energy on these kinds of systems. I am going to make some copies of all these pump curves, because once Grundfos realizes what we can do with this information, it maybe quickly taken off line.


UPDATE:
Finally, I accurately measured the flow against the pressure, this is the Goulds 18GS07 here are the results:
30 PSI @ 23 gpm
35 PSI @ 22.5 gpm
40 PSI @ 20 gpm
50 PSI @ 17.2 gpm
56 PSI @ 14.6 gpm
58 PSI @ 13.7 gpm
68 PSI @ 9.5 gpm
69 PSI @ 8.9 gpm
70 PSI @ 8.5

My free options are either to replace the pump are with the same contractor: Goulds 10GS05 (3 to 16 gpm) or the 13GS05 (4 to 20 gpm) not sure which one. OR I pay for the Grundfos SP16gpm because I would have to use a different contractor - not sure of cost yet. My ideal situation is to use a pump that uses less than 5.4 AMPS so that i can hook it up to the waterfurnace unit so that it can be monitoring. Thoughts
 

Valveman

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Checking the amp draw while you were doing the flow/pressure test would have let you know how efficient that pump is at low flow rates. You can get those numbers on Grundfos pumps from their new selection calculator. But Goulds isn't as forthcoming so you would have to do the amp test yourself, and I am sure the Goulds numbers will not be as good as Grundfos at reduced flow rates.
 

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Checking the amp draw while you were doing the flow/pressure test would have let you know how efficient that pump is at low flow rates. You can get those numbers on Grundfos pumps from their new selection calculator. But Goulds isn't as forthcoming so you would have to do the amp test yourself, and I am sure the Goulds numbers will not be as good as Grundfos at reduced flow rates.


to my surprise, AMPs did not drop by much, the lowest i got was 6.8 from 7.2 amps at the lowest rates. Any clues why?
 

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Static head is the lowest pressure you ever run (usually the start pressure of the pressure switch) converted to feet, then added to the depth to water in the well. In a well where the water level is 100' using a 40/60 pressure switch, the static pressure for the pump would be 192'.
 

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Based on the data above, what is the static head?
I tried 2 points and got 2 different values. Using your highest pressure, I interpolated
105.86 ft for 23 GPM. The 23 psi is 69.2 ft of head. That would leave 33.66 ft difference to represent the static head.

The other point I came up with 176.21 ft at 8.5 GPM from the graph. The 70 PSI is
161.47 ft of head. That leaves a 14.74 ft difference to represent the static head.

I am probably over-computing. And I may have made errors. It is safe to say that since the two points give such different results, I don't think you can use this.
 

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Valveman

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Static head and static water level is two different things. Using your numbers and the curve for the 18GS07 I get anywhere from 19' to 30' for a static water level, which is pretty close for figuring with flow and pressure.
 

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I'm trying to make sense of the numbers to ensure that I have the correct size pump for my need. Most of the research i have done and reading this forum, The pump is over-sized for what my Geo needs as i could not even get it to slow down to 4 gpm. The geo requires a minimum of 4 gpm to 17 gpm. The need for 17 gpm, that means all the heating zones are calling and during this winter, that was rarely needed. Its variable speed compressor that varies the solenoid opening. My disappointment was that i did not have much decrease in amps using the existing pump.
 

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If you are going to use the pump to directly supply the house as well, you will need to stay with a 3/4 HP. A 16S07-8 Grundfos will drop almost 50% in amps at 4 GPM to about .6HP.

However, if you use a two pump method for Heat Pump and house supply, you can use a 16S05-5 to supply the heat pump. It will only produce about 20 PSI at 17 GPM, but that is all the heat pump needs. Then you can add a little jet pump to boost the pressure up to 50 PSI just when and for the house supply. Running the 1/2 HP at 20 PSI for the heat pump will cut the HP required to as little as .38HP at 4 GPM, compared to .6HP using the 3/4HP at 50 PSI.
DUAL PUMP_HEAT PUMP-HOUSE SUPPLY.jpg
 

Ballvalve

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You know guys, with the cost of natural gas going to 1960 levels and likely holding for a few decades, I feel that the days of geo thermal are over. Gotta do what you can to keep your electric costs down, and its informative, but just reading this gave me a huge headache. I think valveman has such a system, and once you "got" it you can't really get out. I barrel tested several pumps and never got more than 1 amp difference between open flow and just cracked open. Don't know how they were stacked, howwever. The complexities of the system and the varied flow requirements are just more than we need in this world that throws curves at every turn. When you figure in the cost of the well and the maintenance, I think it all goes south now with America being energy -more than- self sufficient. Peak oil? Ha! Just a game to keep us paying 5 bucks at the pump like sheep. Right now, red diesel is about $2.60 a gallon in California. I suppose heating oil is much less in the east. I doubt anyone is even considering geo thermal now unless they are in Nevada and live next to a hot spring.

Hey - you could all move to Benton hot springs in California - FAR from the crowds, and all the water comes out of the shallow wells at 130 degrees. You can rent a hot tub for 30 bucks a night and camp there - the water flows into each tub non stop with a cold tap and a valve on the hot to regulate it. Quite amazing as it's in the midst of a high desert. Historically, the Indians lived like kings here - the natural springs put out 800GPM of hot water.
 

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does that change things?

Then you only need the 1/2HP as the Geo also only needs about 20 PSI.

Open loop Geos are really efficient, especially if you have the right pump. But I agree with BV about the low gas prices. However, I have worked in and around the oil industry most of my life, and the one thing you can count on is it will continue to boom and bust. I've seen it at least 4 times in my life.
 

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When you put your pump down, you could add a small flex tubing taped to the down pipe and open near the pump. If you then you blow compressed air at low volume, the air will bubble out at the bottom. The air pressure up top on that tube will tell you how much distance there is from the bottom of the tube to the top of the water water level. The best reading would be right after you turn off the compressor so there is no air flow. You compute 2.3067 feet of water for each PSI.
 

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BV
You know guys, with the cost of natural gas going to 1960 levels and likely holding for a few decades, I feel that the days of geo thermal are over. Gotta do what you can to keep your electric costs down, and its informative, but just reading this gave me a huge headache. I think valveman has such a system, and once you "got" it you can't really get out. I barrel tested several pumps and never got more than 1 amp difference between open flow and just cracked open. Don't know how they were stacked, howwever. The complexities of the system and the varied flow requirements are just more than we need in this world that throws curves at every turn. When you figure in the cost of the well and the maintenance, I think it all goes south now with America being energy -more than- self sufficient. Peak oil? Ha! Just a game to keep us paying 5 bucks at the pump like sheep. Right now, red diesel is about $2.60 a gallon in California. I suppose heating oil is much less in the east. I doubt anyone is even considering geo thermal now unless they are in Nevada and live next to a hot spring.

Hey - you could all move to Benton hot springs in California - FAR from the crowds, and all the water comes out of the shallow wells at 130 degrees. You can rent a hot tub for 30 bucks a night and camp there - the water flows into each tub non stop with a cold tap and a valve on the hot to regulate it. Quite amazing as it's in the midst of a high desert. Historically, the Indians lived like kings here - the natural springs put out 800GPM of hot water.


Hi BV, i tend to mostly agree with you, however, prices will fluctuate with politics more than anything else.
On the pump, i'm having a hard time understanding on why the pump will slow down when restricting the discharge valve? from a scientific perspective, if i restrict flow, the pump will work harder to keep the flow at the same rate. In my own experience, my Goulds pump AMPs barely dropped when restricting the valve. So i'm looking for a pump the smallest pump that will deliver what i'm looking, NOT at peak times, but rather at normal times. Normal operation requires (4 to 10 gpm). that is what my system has been running 80% of the time. I'm even thinking can i have 2 pumps form the same well? OR have a pump booster as per valveman's suggestion when i need higher demands?
 

Texas Wellman

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BV



Hi BV, i tend to mostly agree with you, however, prices will fluctuate with politics more than anything else.
On the pump, i'm having a hard time understanding on why the pump will slow down when restricting the discharge valve? from a scientific perspective, if i restrict flow, the pump will work harder to keep the flow at the same rate. In my own experience, my Goulds pump AMPs barely dropped when restricting the valve. So i'm looking for a pump the smallest pump that will deliver what i'm looking, NOT at peak times, but rather at normal times. Normal operation requires (4 to 10 gpm). that is what my system has been running 80% of the time. I'm even thinking can i have 2 pumps form the same well? OR have a pump booster as per valveman's suggestion when i need higher demands?
Work is force over distance. In your case work is simply the amount of water moved, not the pressure. The less water moved the less work done.

I think you're way over-thinking this one. You've been given good advice now you just need to execute.
 

Valveman

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The pump doesn't "slow down" when restricted with a valve, it actually speeds up a little. As TW said, it is moving less water so there is less work. The amps actually drop, even though the motor speeds up. Do the same test with a hair blower or a vacuum cleaner. When you hold your hand over the discharge, you can hear the motor speed up. If you use an amp meter, you will see that the amps decrease.

The pump you have was not designed to do this very well, but the amps still drop a little. Some pumps are much better at dropping amps than others. It was probably an accident by design, but still some will drop 50% or more.

Look at the horsepower (HP) curve on the bottom of the pump curves I posted. These are 3450 RPM curves, not variable speed curves. Yet notice that the HP drops from .71HP at 17 GPM to .38HP at 4 GPM. My 2HP Grundfos drops from 12 amps when using 25 GPM to 4 amps when running a 3 GPM drip system. That is why I showed you those curves. That is a natural characteristic of a centrifugal impeller pump, you don't have to vary the speed to see a decrease in energy use. You just have to pick a pump that naturally has a good drop in HP if you want it efficient at low and high flow rates.
 
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