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1

Open Loop Geothermal Heat Pump / Re: Geo Heat Pump with Low Pressure Well Pump Saves Energy

« on: March 07, 2016, 12:37:52 PM »

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?

2

Open Loop Geothermal Heat Pump / Re: Geo Heat Pump with Low Pressure Well Pump Saves Energy

« on: March 07, 2016, 08:20:02 AM »

My previous post incorrectly references Emerson as the VFD manufacturer.

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

3

Open Loop Geothermal Heat Pump / Re: Geo Heat Pump with Low Pressure Well Pump Saves Energy

« on: March 06, 2016, 02:50:58 PM »

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?