Geo Heat Pump with Low Pressure Well Pump Saves Energy

[Cary Austin]

Well pump and booster pump to feed house and multiple heat pumps



 Homeowner Info Video
https://vimeo.com/248374321

 Pside-Kick video
https://vimeo.com/248374462

 To cut pumping cost for a heat pump, a two-pump system is recommended. This system uses a 25S10-7 pump end, with a 1 HP motor. This pump would deliver 27 GPM at 100' of lift. Control this well pump with a 20 PSI Cycle Stop Valve, a small pressure tank, and a 10/30 pressure switch. After the pressure tank, one line tees off to the heat pump, another tees off to a booster pump for the house. Use about a 3/4 HP jet pump with it’s own Cycle Stop Valve set at 50 PSI, and a 40/60 pressure switch.

 When the heat pump alone is running, an electric discharge valve opens, the pressure tank drains to 10 PSI, and the pump starts. The 20 PSI CSV will vary the flow to match a single 10 GPM heat pump, two 10 GPM heat pumps, or two 10 GPM heat pumps while still providing up to 10 GPM for the house, which a total of 30 GPM. This should cut your pumping cost by more than 1/2 of what a single 2 HP pump can do. When the heat pump shuts off, the electric discharge valve closes, and the CSV slowly fills the pressure tank to 30 PSI, and the well pump is shut off.

 When the house alone is using water, the pressure will drop from 60 to 40 PSI and the 3/4 HP jet pump will start. The 50 PSI CSV will maintain 50 PSI to the house no mater the flow rate being used. This jet pump system is drawing water from the well pump system, so the pressure tank on the well pump system empties as the pressure drops from 30 to 10 PSI, and the well pump is started. The CSV on the well pump feeds exactly as much water to the jet pump booster as the house is using. Both pumps run as long as the house is using water. When the house stops using water, the CSV on the jet pump will slowly fill the pressure tank to 60 PSI, and the jet pump is shut off. Then the CSV on the well pump will slowly fill it’s pressure tank to 30 PSI, and the well pump is shut off.

 When the heat pump(s) is/are running, the well pump/CSV is delivering 10 or 20 GPM at 20 PSI. If the house needs water at the same time, the jet booster pump comes on, and the CSV on the well pump opens up to supply both the heat pump and the jet booster pump. With a 100' pumping level, you should be able to get 30 GPM total when the house and both heat pumps need water at the same time. When the house no longer needs water, the jet pump system will fill it’s pressure tank to 60 PSI, and the jet pump is shut off. Then the CSV on the well pump reduces the flow to 10 or 20 GPM, matching the amount used by the heat pump(s). Again, when both heat pumps are shut off, the well pump fills it’s pressure tank to 30 PSI, and both pumps stay shut off until water is needed again.

 Reducing the main well pump from a 2 HP to a 1 HP will cut the pumping cost considerably. The only time both pump will run at the same time is when water is being used in the house. The house will use very little water compared to the heat pumps, so the added electric for the booster pump won’t add up to much. If the system is also used for irrigation about 500 hours a year, both pumps will run this amount of time.

 The 2 HP single pump system with CSV described earlier will use $942.00 per year, or $78.50 per month.

 The 2 HP single pump system with VFD described earlier will use $751.00 per year, or $62.58 per month.

 The 2 pump system with CSV control described here will use $631.00 per year, or $52.58 per month.

 The 2 pump system will save considerable energy over a single pump system. Using CSV controls, these pumps should last a long time, which is what really saves the most energy. The savings for using a two-pump system is $311.00 per year or $25.92 per month.

[Raindrops]

Got a Emerson constant pressure VFD for my whole house and a "pump and dump" 2 ton earth coupled heat pump. Have had the sensor go bad and had to pull the pump once for a check valve failure. Not too happy but we enjoy the constant pressure.

The heat pump runs at ~ 3GPM and because I need a Centaur Carbon filter there is a whole house flow restricter of 4GPM. The heat pump runs for long periods, sometimes for a couple of hours in weather extremes. Don't need the 15GPM of the Emerson.

The long heat pump run times would expose the 150 foot deep submersible pump to significant increased back pressure if I were to additionally install a CSV to the existing system. The well down-pipe is 20' sections of PVC with its multiple threaded joints. I think the Emerson would still have the soft start feature, but I think the 40/60 switch would cause the 15GPM 1-1/2 HP pump to see full 3 phase voltage and possibly high frequency. The resulting current, and thus the power, is not something I can determine. The centrifigal pump does not have any feedback signal in the Emerson system, so I don't know how it will react.

I have analyzed the 240v input to the Emerson, using a Current Transformer, and see the very numerous current fluctuations that you describe.  Exactly how much power it is consuming is debatable, even as to what the electric utility smart meter is registering.

If I had known about the CSV back a few years before the Emerson, I would never installed the Emerson. Your two pump geo system is just what the doctor ordered for someone without a VFD. If I have a major malfunction, I will certainly go to the CSV. But my VFD is still operational and it would cost $$$ to remove and go to the CSV.

Is there a way to use a CSV on my existing system?

Would it be beneficial?

[Raindrops]

My previous post incorrectly references Emerson as the VFD manufacturer.

The correct manufacturer is Franklin and the specific unit is the SubDrive 75.

[Cary Austin]

My previous post incorrectly references Emerson as the VFD manufacturer.

The correct manufacturer is Franklin and the specific unit is the SubDrive 75.

Yes you can use a CSV with a "subdrive".  Just replace the pressure sensor with a standard 40/60 pressure switch and install a CSV1A set at 50 PSI in front of the pressure tank or any water line tees.  The Subdrive will still convert the single phase power to three phase, but it won't be variable speed.  The CSV will still make it variable flow without varying the speed.  This will stop the bouncing on and off 45 times a minute that you are seeing with the subdrive.  This can be very beneficial for many of the pump system components.

When the pump quits, just be sure to go back with a normal single phase pump and you will already have the CSV set up to control it as needed.

[Raindrops]

Cary, Thanks for the reply.

With my concern about high head pressure, I dug out the SubDrive 75 pump sizing diagram (My static head pressure is in the 110 PSI range). It shows that if the CSV provides flow control with back pressure, at a 3GPM flow the necessary head pressure will be the equivalent of a ~575 foot deep pump; which equates to about a 300 PSI head pressure. I assume the SubDrive would be operating at high voltage and frequency (~90 Hz). I would not be surprised that the VFD would not be able to determine the difference of CSV pressure bump versus a very deep well.

I believe your reply about speed control to be correct; I think the SubDrive would go to high speed in a rather short order and remain there. Hopefully, there would be a somewhat gradual speed increase so hammering would not occur (never experience hammering with my current setup), but the head pressure would still be a significant increase over my current operation.

The diagram also shows what 3/4 HP with a 10 GPM pump would produce at 3GPM; it shows about 300 foot deep pump; this equates to about 150 PSI head pressure. A modest increase from my static pressure. I am comfortable with that.

I conclude that the CSV addition to the SubDrive would double the running head pressure. With PVC down pipe and 13 brass couplings, there is the potential for failure.

The addition of a CSV on a standard 3/4 HP 10 GPM pump would not significantly change the head pressure. When pulling a failed SubDrive pump, there is an opportunity to inspect the down pipe and couplings, or go to stronger pieces.

I am inclined to wait until I experience a down-hole failure before switching to a CSV.

Again, I sure would like to set the calendar back so that I could avoid the VFD.

A secondary issue; my well has some hydrogen sulfide which I remove with Centaur Carbon for the domestic water. The geo heat pump uses particle filtered but untreated water; the water heat exchanger is cupro-nickel to be able to survive the hydrogen sulfide. I don't experience any sand or other bad things in the filter media. A CSV will see the unfiltered and untreated water; is there a CSV able to survive the hydrogen sulfide?

[Cary Austin]

A CSV can survive the H2S no problem.  And yes we have a limited amount of backpressure we like to deal with.  But usually you can subtract the static water level in the well from the 575' the pump can build and the back pressure isn't too bad.  So if the static level in the well is say 300', then you only have 275' or 119 PSI of backpressure to deal with.