Hi folks,

I recently added a VFD to my existing open loop system to drive my submersible well pump and wanted to share my experience. I have a 5 ton geo running off a 1hp 22gpm well pump and came to realize the well pump is killing my efficiency (thanks to my recently installed an energy monitoring system). In cooling mode (stage one) my GSHP is using about 1800w, with the well pump also using 1800w. To throttle down the pump I have it running 15gpm at 70psi (to prevent it from cycling while geo is on).

My goal was to keep the existing setup (water tank/pump) and run the geo at a lower pressure, thereby reducing energy waste. After putting in the VFD the well pump runs about 400 watts, down from 1800w! I purchased the Pentek Intellidrive controller (PID20), and have it set to supply 15psi through transducer (going to geo), but have a second setpoint of 70psi, which is enabled just when the old pressure switch closes (set to run 35-55psi)-doesnt actually hit 70psi on transducer. This is protected from geo supply branch by a check valve so house pressure never falls when geo is on - also has a large reserve due to existing tank. So pump runs at about 35hz 400w unless house pressure falls below 35psi then ramps up to 1800w at 60hz until pressure switch clicks off.

The Pentek vfd also has a built-in relay which I have wired to the flow switch input on the geo, so if pump/vfd errors out it will stop geo. I have been very happy with the configuration of the Pentek drive and it's performance. Only regret is not having done it sooner - I installed the geo about five years ago.

My COP for heating went from 2.89 to 4.1, and cooling from 4.2 to 6.7 (stage1), including well pump. I think this is actually higher than a comparable closed loop setup.

Estimated payback for the VFD to be a little over four years.

Is the well pump single phase?

Yes it is a single phase three wire pump.

How much does it cost? List price is close to retail for a complete Grundfos SQE setup (including pump).

I expect that something similar could be done to adjust the pressure sensor output on a Grundfos to get dual pressures.

Posted By jonr on 03 Jun 2015 10:07 AM
How much does it cost? List price is close to retail for a complete Grundfos SQE setup (including pump).

I expect that something similar could be done to adjust the pressure sensor output on a Grundfos to get dual pressures.

I considered the Grundfos SQE setup but chose the Pentek drive for several reasons:

My cost for PID20 was $1150 Canadian before taxes (could have used a PID10), local Grundfos quotes were at least double that (including pump), granted I could have bought out of the States for probably $700US with pump and CU301.

Didn't like that with Grundfos I was stuck with a 11k rpm pump and their unique system. Wasn't sure about long term durability and support. With the Pentek I can put any motor on, including 3 phase if I have to replace down the road.

Configurability was much, much better on Pentek, as I could adjust PID settings if I have problems with surging etc, as well as built-in dual system pressure setpoints, and relay output. Also sleep and wake parameters are configurable (although I wish I could just disable sleep altogether as I use second digital input for "Run Enable", so pump shuts off immediately after geo or pressure switch stop call for water, otherwise pump runs for 1 minute with no flow, although only at 250watts 30hz.

I didn't really want to get into putting in resistors and relays inline with transducer on Grundfos setup to trick it down to 15psi for geo or full open/high for house pressure.

This way it will run well on generator too, and I still have a large reserve with existing 20gallon draw tank. Also there was minimal changes to existing setup - no removing tanks or pulling well pump. Just a bit of plumbing changes and wiring.

Have some pics to attach but not sure why it's not showing up inline in post, just links. Maybe Chrome browser problem? Anyway for well pressure switch one contact enables vfd, the other enables second setpoint (70psi). The relay isolates the Y signal from thermostat, both use 24vac from GSHP.

At that price, I agree with your reasoning.

Want to thank Blake Clark for his posting regarding his use of Grundfos SQE at 10psi (below), as it provided valuable guidance for me on optimizing my well pump and taking it from 1800watts (7.5amps) to 450watts (1.9amps). I could probably reduce further as he did if I changed my set pressure to 10psi instead of 15. In fact, I found very little online by way of hard numbers and examples of people reducing the energy used by open loop geothermal well pumps. I am still very questionable as to whether a cycle stop valve would do much to reduce pump energy, certainly not the 400% reduction I now get.

I believe my well pump is actually operating at less watts than the circulating pumps on a closed loop system (dual ones anyway).

Here's the post by Blake:

Is there a more efficient well pump besides the standard jet pump?
http://www.greenbuildingtalk.com/Forums/tabid/53/afv/topic/aff/13/aft/80320/afpg/2/Default.aspx

Should also mention that my pump/motor/vfd is operating at 32% efficiency on the reduced pressure. Based on head and flow it should be 146w at 100% eff (at 15psi). The big question that I had going in - what type of efficiency loss would I see going from full load to nearly half speed (substantially less load). Nobody I talked to was able to answer this.

Another factor was cooling for the pump motor (as it isn't monitored like the Grundfos SQE pump is). According to my pump literature, the pump requires 13 gpm of flow based on a 6" well casing, so I should be fine there - but certainly something you should check as the pump may be operating for hours with the geo on.

Nathan

You can look at typical pump efficiency curves - they vary widely. While there is only one point with maximum efficiency, a typical pump will remain good at least down to 1/2 of max output. Some go much further (< 20%). Don't oversize.

My guess is that power consumption (heat generation) and flow track well enough to not be a problem at any reasonable flow (edit: looks like down to about 20% of flow at best efficiency). Less true with throttling.

Grundfos should offer an off-the-shelf dual pressure option.

Do not forget the installation of VFD cooling fan.
here's a post by a specialist: http://www.veichi.org/variable-frequency-drives.html

Posted By Nathan on 04 Jun 2015 09:16 AM
I am still very questionable as to whether a cycle stop valve would do much to reduce pump energy,

When maintaining a single set pressure the CSV can reduce the energy use almost as much as a VFD. But anytime you can reduce the pressure, reducing the pumps speed will lower the energy consumption.

Posted By Nathan on 04 Jun 2015 10:25 AM
Should also mention that my pump/motor/vfd is operating at 32% efficiency on the reduced pressure. Based on head and flow it should be 146w at 100% eff (at 15psi). The big question that I had going in - what type of efficiency loss would I see going from full load to nearly half speed (substantially less load). Nobody I talked to was able to answer this.

Another factor was cooling for the pump motor (as it isn't monitored like the Grundfos SQE pump is). According to my pump literature, the pump requires 13 gpm of flow based on a 6" well casing, so I should be fine there - but certainly something you should check as the pump may be operating for hours with the geo on.

Nathan

Your VFD is telling you the pump is running at 32% efficient. This is better than doing the calculations. A normal submersible pump of this size is about 55 to 60% efficient at best. You could actually use even less energy with a pump sized to the demand and running at full speed and at its best efficiency point. Which is what I would do with a CSV, then I would use a little booster pump to increase the pressure to the house when house water is needed.

Posted By Nathan on 04 Jun 2015 10:25 AM
Another factor was cooling for the pump motor (as it isn't monitored like the Grundfos SQE pump is). According to my pump literature, the pump requires 13 gpm of flow based on a 6" well casing, so I should be fine there - but certainly something you should check as the pump may be operating for hours with the geo on.

Nathan

Cooling flow is a problem with VFD when using very low flow rates. The harmonic content of the power from a VFD means that the cooling flow is the same as for a pump running at full load amperage. With a CSV the motor is running on standard sinusoidal power and the motor load is de-rated. This means the motor can safely operate down to as little as 1 GPM and remain cool.

Posted By VeichiElectric on 26 May 2016 02:59 AM
Do not forget the installation of VFD cooling fan.
here's a post by a specialist: http://www.veichi.org/variable-frequency-drives.html

And yes make sure to keep the air filter clean and the VFD itself cool and maybe you will make it to the 4 year payoff needed. I have VFD's on some plastic injection machines that I keep an extra air conditioner pointed at to keep them from tripping out.

Hey Valveman, welcome to the thread! I checked out cyclestop valves too but decided to go this way. The VFD and single phase pump has been working excellent for over a year now and this year saved $900 in electricity with the VFD change and a change to my hotwater whole home distribution system.

You definitely have to do the math for cooling flow to the well pump. There needs to be a minimum linear flow of water past the pump, so it needs to be moving enough water to cool itself. Also the VFD itself has a fan on, but rarely runs unless pumping at full speed which is minimal. So far no failures, but time will tell I guess.

I recently filled my pool with 17,000 gallons by running the output of my geo directly to the pool, and leaving the AC on all day. The pump ran at nearly half speed for about 11 hours, I stopped it twice for 1/2 hour. Helped put warmer water into pool than cold well water. Also, pump didn't cycle which I think is one of the main things that kills them.

Nathan P.S. I don't really care about the efficiency of the pump, just that it was dropped from 1800w to 400w with the VFD. I like that it is a bit oversized as it can kick into high gear and fill the house pressure tank while still delivering 14 gpm to heat pump at up to cutout pressure of 60-70psi.

Posted By Nathan on 05 Jul 2016 09:41 AM
Hey Valveman, welcome to the thread! I checked out cyclestop valves too but decided to go this way. The VFD and single phase pump has been working excellent for over a year now and this year saved $900 in electricity with the VFD change and a change to my hotwater whole home distribution system.

You definitely have to do the math for cooling flow to the well pump. There needs to be a minimum linear flow of water past the pump, so it needs to be moving enough water to cool itself. Also the VFD itself has a fan on, but rarely runs unless pumping at full speed which is minimal. So far no failures, but time will tell I guess.

I recently filled my pool with 17,000 gallons by running the output of my geo directly to the pool, and leaving the AC on all day. The pump ran at nearly half speed for about 11 hours, I stopped it twice for 1/2 hour. Helped put warmer water into pool than cold well water. Also, pump didn't cycle which I think is one of the main things that kills them.

Nathan P.S. I don't really care about the efficiency of the pump, just that it was dropped from 1800w to 400w with the VFD. I like that it is a bit oversized as it can kick into high gear and fill the house pressure tank while still delivering 14 gpm to heat pump at up to cutout pressure of 60-70psi.

With a VFD you have to make sure to get your 0.5 feet per second flow past the motor, which is why you need a minimum of 13 GPM in 6" casing. As I said the CSV de-rates the motor load so much that it doesn't need the same 0.5 fps to stay cool as the VFD controlled motor does. If the VFD is in the house where the air is cool, the cooling fan in the VFD is all you need. Just make sure to keep the lint filter clean so it can get the cool air it needs. Running water from the discharge of the heat pump to the pool is a good idea for several reasons. It puts warmer water in the pool, and as you said, it doesn't cycle the pump on and off like when you run in the higher pressure mode using the 35/55 switch and tank. I actually use the heat pump discharge to feed the house as well. That way the pump can be smaller as it doesn't have to produce the 15 GPM the heat pump needs plus an additional 5-7 GPM for the house, which is why you have a 22 GPM pump. If you supplied the house through the heat pump discharge, a 15 GPM pump is as large as you need. The water in the house is just 10 degrees warmer or cooler depending on the season (AC or heat mode). That looks like a good set up, except if you had any irrigation which needs the higher pressure, the pump would be cycling a lot. You are also not getting the benefits of constant pressure in the house as the pressure will keep cycling between 35 and 55.

Good points! I already had the pump setup so it would be interesting to look at a two pump/booster setup if I did it all over again. Currently looking into a water to water heat pump running off discharge of existing GSHP for heating my pool. Their efficiency aren't as good - only 4 COP but better when pool is colder (spring/fall).

Trying to decide on regular air source heat pump or geo for pool. Any thoughts on that? Nathan

When running the existing heat pump is the AC mode, any heat you get out of the discharge is completely free. If the pool needs filling, I would fill it directly with the discharge from the heat pump as you did previously. If the pool does not need filling, you could run the heat pump discharge through another heat ex-changer to heat the pool. I would think these things would eliminate the need for any additional heating for the pool.

Posted By Nathan on 04 Jun 2015 09:16 AM
I am still very questionable as to whether a cycle stop valve would do much to reduce pump energy,

While I don't have a horse in this race, I would encourage people to do their own due diligence regarding CSV's.  Valveman's claims and rebuttals from others should still be available by searching https://www.geoexchange.org/forum/

If I recall correctly, Valveman has a direct financial interest in selling CSV's and if I also recall correctly, he was banned from that site.

Posted By geome on 05 Jul 2016 07:06 PM

Posted By Nathan on 04 Jun 2015 09:16 AM
I am still very questionable as to whether a cycle stop valve would do much to reduce pump energy,

While I don't have a horse in this race, I would encourage people to do their own due diligence regarding CSV's.  Valveman's claims and rebuttals from others should still be available by searching https://www.geoexchange.org/forum/

If I recall correctly, Valveman has a direct financial interest in selling CSV's and if I also recall correctly, he was banned from that site.

Yes PLEASE do your due diligence on CSV's. You will see that I am the owner and inventor of the CSV. And you will see that we have been doing this since 1993 and have never had any problems as many will try to make you believe. I could make a lot more money selling VFD's, but I sell CSV's instead because it is the right thing to do, not because they make me the most money. And yes I was banned from geoexchange.org because they want an exorbitant amount of money from any manufacturer to even mention their product. While the installers only have to pay $500 to be a member and be able to say anything they want. And they will say whatever makes them the most money, not what is best for the homeowner. I was glad to find this forum on heat pumps, as I am certain you will not get accurate information at geoexchange, especially because I do not post there. But please go back and read everything I said there as it is 100% accurate, which they don't want to hear, and is the main reason I was banned. But please also do your due diligence on geoexchange.org and you will see that you only hear what the dues paying members want you to hear. It is not an open exchange of ideas as it should be.