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

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Digital Geek

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my first thread here,

I have a standing water column for my geothermal Heat Pump. My pump installer screwed up on the pump sizing. Initially put a smaller pump 10GS05 and then larger pump 18GS07 with M07412. Right now, the pump is pumping 26 gpm, which is extremely unnecessary and consuming a lot of power. My geo unit is a waterfurnace series 7 and is variable speed compressor. So it needs 17gpm at max, and at 80% of the time requires about 8 to 9 gpm. The geo demand is between 4 to 17 gpm. So after extensive research, the pump installer is suggesting installing a 1AS15 VFD and call it a day. I'm not convinced. However, I'm very concerned about power consumption.

The WELL is used for the geo and nothing else and the water is returned to the well.
  • Depth: 605'
  • well static 29' from grade,
  • an additional 22' to house (not sure what this means)
  • 18gs07412 Goulds Submersible
  • recovery 3gpm
  • 500' of Shroud
Goulds technical line provided me with the following setup providing the best efficiency:
· 13GS05 pump (3 wire)
· M07432 motor, yes ¾ HP
· 3AS20 VFD (single phase input and 3 phase output)
Pump installers does not like the above setup and says it does not make sense.

further reading I see that I can do a 13GS05 (2 wire) and M05422 with 1AS15 VFD

I'm completely lost and desperately looking for help. right now, i can simply add the 1AS15 VFD because i have to wait for spring to get to the pump

Any guidance or recommendations would be much appreciated.
 

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My geothermal is designed to work around 5000 hours a year, so power consumption is very important. I appreciate any feedback.
 

Valveman

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I would use a 16S05-5 Grundfos pump with a 1/2HP single phase motor. You want to start out with the smallest horsepower pump that will do the job. Then if you use the Grundfos pump, the amps will drop by 30% to 40% when you valve the flow down from 17 GPM to 4 GPM. You don't need a Variable Speed Drive to make the amps drop on the pump. You just need to pick a pump that has a natural amp drop like the Grundfos. The Goulds 13GS05 would work about as good, but because of the impeller design the amps will probably only drop 15% to 20%.

I hear from lots of people with open loop geo systems. Many of them tell me it doesn't matter how much energy the heat pump is saving because they spend 3 times that much keeping the Variable Speed Pump working. A standard RPM pump with a normal single phase motor hooked directly to the heat pump will last many times longer than any variable speed device and/or pump.

Oh and get a three wire motor with a CSCR (capacitor start capacitor run) control box. The capacitor run will save even more energy.

If you want to save money and get a real return on your investment, it is important that all the expensive equipment last a long time.
 

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I really appreciate your feedback and quick response. How will the geo control the speed of the pump/motor? with a VFD, the geo solenoid valve changes the flow which triggers an increase/decrease in pressure which lowers/increases the motor speed to keep constant pressure (that is the way it was explained to me). How will that work with a constant speed pump?
 

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Nothing needs to control the speed of the pump. Even though the pump runs at 3450 RPM all the time, it will only draw power according to how much water you are using. If you open a valve and let it pump 17 GPM it will pull a full 1/2HP load. If you restrict the flow with a valve to 4 GPM, the load will drop by almost 50%. This is a natural characteristic of a centrifugal pump. People who do not understand pumps think you need to vary the RPM to decrease the amp draw, which is absolutely false.

Usually there are three separate heat pumps which each uses maybe 6 GPM. When only one heat pump is on the well pump is restricted to 6 GPM. When two heat pumps are on the well pump supplies 12 GPM, and with three heat pumps it supplies 18 GPM.

If you have a single heat pump that needs the flow to vary from 4 GPM to 17 GPM, you can put three solenoid valves on the discharge of the heat pump. One valve activated gives you 6 GPM, two gives 12 GPM , and three delivers 18 GPM. And the power to the well pump will vary according to how much water you are using, without a variable speed drive and all the problems that go with.

The heat pump doesn’t care what pressure the water is coming in at, all it cares about it the flow rate. With a 16S05 pumping from 30’ the pressure on the heat pump will be 25 PSI when running 17 GPM and 51 PSI when the flow is reduced to 4 GPM.

If you want the heat pump to see a steady 20 PSI, just use a Cycle Stop Valve set at 20 PSI. But if your well pump is turned on and off by the heat pump controller, I don’t thing you need anything else.
 

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thank you for such level of detail. What you are proposing a CSV set at 20 with 16S05-5 Grundfos pump with a 1/2HP single phase motor.

I noticed that you are not favoring VFD, any thoughts?

My current issue is that the setup was just done in Dec, my installer will switch out the pump but will stick to Goulds. So if i do changes pumps because of savings, that means i will have an extra pump that i'm not sure what i will do with.
 

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500' of Shroud

Just trying to follow.... Does this means that the pump is actually mounted down maybe 50 or 70 feet, but a PVC shroud pipe (like a flow inducer) goes over the outside of the motor and down 500 more feet to draw the water from near the bottom to get a better temperature? Or is the pump fairly close to the bottom, an "shroud" is being used as a synonym for casing?
 

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Just trying to follow.... Does this means that the pump is actually mounted down maybe 50 or 70 feet, but a PVC shroud pipe (like a flow inducer) goes over the outside of the motor and down 500 more feet to draw the water from near the bottom to get a better temperature? Or is the pump fairly close to the bottom, an "shroud" is being used as a synonym for casing?

i forgot to mention that the pump is located at 140' and the PVC/Shroud is pulling water from the bottom for better temperature differential. THe water is returned to the well at 45'.
 

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thank you for such level of detail. What you are proposing a CSV set at 20 with 16S05-5 Grundfos pump with a 1/2HP single phase motor.

I noticed that you are not favoring VFD, any thoughts?

My current issue is that the setup was just done in Dec, my installer will switch out the pump but will stick to Goulds. So if i do changes pumps because of savings, that means i will have an extra pump that i'm not sure what i will do with.

I was building, programming, and installing VFD's more than 25 years ago. I like to say I am an expert on VFD's, which is why I would never use one on a regular pump application. I know you are a "Digital Geek", but the VFD is one thing that is greatly myth-understood and myth-used on many applications. There are a few good applications for VFD's, but for regular water pumps they are a good way to scam people out of their hard earned money. See this.. http://www.cyclestopvalves.com/vfd-energy_15.html

Even your 18GS07 will use less energy if you restrict the flow as needed. If you are letting it pump 26 GPM, you are always using max power. If you restrict it to 17 GPM, it will probably use about 20% less energy. If you restrict it to 4 GPM, it will probably use 30% less energy than when running 26 GPM. That way you are getting the best you can out of the pump you already paid for. A CSV1A would keep the pressure a steady 20 PSI to the heat pump no matter how much or how little flow you are using. Without a CSV that pump will vary from 40 PSI at 17 GPM to 69 PSI at 4 GPM, and the heat pump won't care if the pressure is 40 or 69.

Now a 1/2HP pump would start out using 33% less energy than the 3/4HP. And if you use a Grundfos instead, it will drop to almost 1/4HP load as the flow is restricted to 4 GPM. That would be the least pumping cost you can get away with, and will be almost exactly the same as you could get with a VFD.

Whichever size pump you use, the standard single phase pump/motor being restricted with a valve will last many times longer than a VFD or the pump/motor it controls. You will never save any energy using a heat pump when you have a VFD well pump. Any energy and money you might save varying the pumps speed will quickly be overcome by the continyual repair and replacement cost of the VFD system.

A VFD on a compressor is a completely different animal from a centrifugal pump. A compressor will use less energy when controlled by a VFD. But the VFD still has to last long enough to get a Return On your Investment.
 

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Valveman, thank you so much. this is very helpful and i'm seriously considering replacing my pump with what you are recommending. My apologies for my additional questions.:
- What is the exact model of the pump?
- Do i need a control unit with it? which model?
- What model CVS, specs and where is it installed?
The cost above could be less than what my pump installer is asking to install the VFD which is 1500.
My heat pump runs about 5000 to 6000 hours per year and at 70% of the time, it only requires 8 to 10 gpm. The range is 4 to 17gpm.
 

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The cost above could be less than what my pump installer is asking to install the VFD which is 1500.

Ouch!! And that will just be the first of many new VFD's you will pay for over the life of your heat pump. See what I mean? Even if you could get a 5 year warranty on a VFD (which I doubt) that is $300 a year or 25 bucks a month to keep the VFD going. You can have a very inefficient pump system and still be better off, as the standard pump will last many times longer than the VFD system.

The most efficient and longest lasting pump would be the 16S05-5 Grundfos pump with a 1/2HP, 3 wire motor and a CRCS control box. Just tie the well pump to the heat pump controller and let it run whenever the heat pump comes on. You really only need a CSV and a pressure tank if the well pump is used for other things besides the heat pump.

If your heat pump has outputs for Stages 1,2, and 3, you can use that to open 1,2, or 3 solenoid valves to get the varied flow you need as the heat pump requires.
 

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my heat pump is a variable speed (Waterfurnace 7series - 12 stages) and requires a constant pressure. multiple Solenoid is not an option because the one I have installed has variable opening and is controlled by the heatpump. So depending on the heat pump demand for flow, it adjust the solenoid valve opening and pressure increases or decreases triggering the VFD or CSV to increase/decrease pump speed (currently no VFD or CSV).

Sounds like my immediate fix is to install a CSV with my current pump (least expensive and quick) and then replace the pump in spring when snow melts providing access to the well.

Thoughts?
 

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If your heat pump can vary the opening of a solenoid valve, then why is it letting 26 GPM through when you only need 17 GPM? You would need a motorized ball valve or something to make that happen. I have never seen a variable solenoid valve.

The CSV and/or the VFD can both give you constant pressure. But the flow rate is still determined by the opening of the solenoid valve.
 

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If your heat pump can vary the opening of a solenoid valve, then why is it letting 26 GPM through when you only need 17 GPM? You would need a motorized ball valve or something to make that happen. I have never seen a variable solenoid valve.

The CSV and/or the VFD can both give you constant pressure. But the flow rate is still determined by the opening of the solenoid valve.


Currently is configured open at 90%. when it was set to variable, the pressure changes and the pump starts cycling causing an error on the heat pump. So it was left at 90% for now until we either install the VFD or now based on your recommendation the CSV.
 

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I recently had some geo-therm experiences. One I looked at (Water Furnace) has a solenoid on the water inlet. The unit measures the difference between water temp in and water temp out. It adjusts the solenoid to get the spread it's looking for (maximum efficiency). It doesn't care about pressure, only delta T.

The other one I looked at only had a set amount of water flowing through and you had to manually adjust a valve to get the right flow of water.

I have heard of those standing-column designs before and a lot of people do not believe they will work. You noted that your well recovery rate is 3 gpm and you're using 17 gpm. The pump pulls the water up from deep in the well and then dumps the return into the top of the well. I guess the hot incoming water is supposed to mix with the cool water deeper in the well but I don't see how it keeps the well from heating up over days or weeks of use.

Are you in a Texas Climate or New England? Your avatar is Tx but your location says MA.
 

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Currently is configured open at 90%. when it was set to variable, the pressure changes and the pump starts cycling causing an error on the heat pump. So it was left at 90% for now until we either install the VFD or now based on your recommendation the CSV.

So your pump is cycling, which means you have a pressure tank and pressure switch. You don’t need a pressure tank and switch unless the water is also being used for the house or something else. If the pump is dedicated to the heat pump, just tie the pump wires to a relay that starts and stops the pump with the heat pump. You will have 40 PSI at 17 GPM and 69 PSI at 4 GPM, but you should be able to adjust the solenoid to work with that. If not just add a CSV1A so you can set the pressure to hold a steady 20 or 30 PSI no matter the flow rate.

Right now you are running at 90% and 26 GPM just to keep the well pump from cycling. You can also use the CSV with the pressure tank and switch if you like. Either way it will let you vary the flow to the heat pump without cycling the well pump.


I recently had some geo-therm experiences. One I looked at (Water Furnace) has a solenoid on the water inlet. The unit measures the difference between water temp in and water temp out. It adjusts the solenoid to get the spread it's looking for (maximum efficiency). It doesn't care about pressure, only delta T.

Yeah heat pumps don’t care about pressure. They are only concerned with the flow needed to maintain the Delta T or temperature differential.

I have heard of those standing-column designs before and a lot of people do not believe they will work. You noted that your well recovery rate is 3 gpm and you're using 17 gpm. The pump pulls the water up from deep in the well and then dumps the return into the top of the well. I guess the hot incoming water is supposed to mix with the cool water deeper in the well but I don't see how it keeps the well from heating up over days or weeks of use.

If the well has any flow underground heat build up is not a problem. If there is no flow in the well they use a “bleed” system that discharges maybe 1 GPM, or as much as is needed to keep the well from heating up. You just don’t want to bleed enough to lower the static water level as the higher level means less energy used by the well pump.
 

Reach4

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I have heard of those standing-column designs before and a lot of people do not believe they will work. You noted that your well recovery rate is 3 gpm and you're using 17 gpm. The pump pulls the water up from deep in the well and then dumps the return into the top of the well. I guess the hot incoming water is supposed to mix with the cool water deeper in the well but I don't see how it keeps the well from heating up over days or weeks of use.

I was thinking that in the winter the warmer incoming water would be cooled by the well bore on its slow travel down. Then the cooler water that had worked its way down would get drawn from the bottom. One thing that would be fighting you is that the conduction of the shroud would be warming the water coming back up by the warmer water going down. If that shroud is 4 inch diameter, that could be considerable. If the pump were near the bottom with 1 inch pipe sending the water up, the water would be warmed less on its way back up.
 

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I'm in New England so water heating up is not a problem. I have not changed the avatar yet. I just singed up and was looking for help to resolve my pump situation.

My bleed scenario is more likely in the winter than the summer.

I really appreciate all the feedback. This have been really great. I'm talking to my pump installer and will report on progress.

What is the easiest quickest way to measure pump consumption? Something that i can install to monitor progress.
 
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