Hey Turbo thanks for chiming in. You are setting up a really good test. Be sure and set the PID at the same pressure as the CSV to get a good comparison. And if you could give us the model number of the pump, depth to pumping level, and GPM required for the heat pump, we could give you more data.


I would like to do the math and see how close I could get to your real life test. So KWh readings from the past to compare with future would be great. If there was anyway to verify the number of hours per month the heat pump runs it would be good to make sure they are the same. But a years worth or two might average things out well enough.

Of course we will need to use KWh numbers as the rates have doubled. And I will still bet that with a little testing and proper sizing, a much smaller standard speed pump could be used, which would be the lowest energy cost possible.


Rolf thanks as well. Simplicity is art. And you have one of the simplest and best set ups I have heard of. The storage tanks can filter the sediment, deliver water at low pressure and varied flow rates, keeps the pump from cycling and always running at it's most efficient point.

I wish I could do the same. But in Lubbock we have no elevation to work with. As they say around here, "it is so flat you can see your dog running away for three days".

I currently have the same setup as the OP did before he converted to VFD. I also have the same problem concerning water pumping costs. I installed a CSV this season after a premature pump failure, and it is working great for what I wanted it to do - eliminate most of my pump cycles. However, now when GEO runs, it holds pump on 100% of the time - without also cutting power usage, and this has caused my pumping cost to more than double. So, now I am looking to solve that problem, and came across this thread. In reading the OP's setup however, I am a bit confused how these two set points are setup and work. If you just have GEO, set at say 15PSI from the transducer and that's the only thing plumbed - it seems pretty straight forward. But, based on the description, I am envisioning for someone like me who has a dual purpose well pump (GEO and domestic water usage) that a tee is added prior to the transducer, with a check valve installed on the outlet that goes to the GEO. That would mean the pressure tank is prior to all of this, so how can existing pressure switch be used to control a second set point above 15PSI? If the GEO was only thing consuming water, and set at 15PSI, wouldn't the pressure tank bleed down below cut-in (let's say 40PSI) for domestic every time. Can anyone help me understand, as I am clearly missing something. Thanks!

Hi Dave, thanks for the question! I took a pic of my configuration, as well as added some notes. Basically I have a T coming off the pump, with one side going to geo (with a transducer set at 15psi), and the second side going through a check valve to a domestic water tank. That tank has a manual pressure switch which, when it closes tells the VFD to turn pump on at full RPM until pressure switch hits 60psi. If the geo is running the geo would also see 60psi and therefore takes several additional minutes of running to fill tank (because it's running 12GPM through geo and filling domestic tank, at 60PSI). At any rate depending on how your pump is sized it may continue to run at full RPM until geo shuts off or it can satisfy pressure at domestic tank, then drop back to 15psi. I am very pleased with my setup and no longer hear my geo electronic ball valve open and close (I had to set to 80psi due to my size pump/head to maintain pump running with geo on prior to VFD, as a result the valve opening and closing at that pressure was fairly loud. Anyway, if you have further questions I would be happy to help. BTW, I have a steam humidifier installed as well as hot water recirc pump for instant hot water throughout house. cheers, Nathan

I should also mention that due to a bug in the VFD's firmware do not use the run enable command on the Pentek intellidrive.

Nathan, Thanks! That was really helpful. So if I'm understanding your setup you took the O1 +/- lines and wired them to one side of the old 40/60 PSI switch, and the I1 +/- to the other side of the pressure switch. Then you program the controller to turn on at the second set point when there is voltage on the I1 +/- lines?

Posted By Nathan on 15 Feb 2017 12:43 PM
Hi Dave, thanks for the question! I took a pic of my configuration, as well as added some notes. Basically I have a T coming off the pump, with one side going to geo (with a transducer set at 15psi), and the second side going through a check valve to a domestic water tank. That tank has a manual pressure switch which, when it closes tells the VFD to turn pump on at full RPM until pressure switch hits 60psi. If the geo is running the geo would also see 60psi and therefore takes several additional minutes of running to fill tank (because it's running 12GPM through geo and filling domestic tank, at 60PSI). At any rate depending on how your pump is sized it may continue to run at full RPM until geo shuts off or it can satisfy pressure at domestic tank, then drop back to 15psi. I am very pleased with my setup and no longer hear my geo electronic ball valve open and close (I had to set to 80psi due to my size pump/head to maintain pump running with geo on prior to VFD, as a result the valve opening and closing at that pressure was fairly loud. Anyway, if you have further questions I would be happy to help. BTW, I have a steam humidifier installed as well as hot water recirc pump for instant hot water throughout house. cheers, Nathan

Your energy use is high for a couple of reasons. You have a brand of pump that does not reduce in amps when the flow is restricted. some pumps will reduce in amps much more than others. You can use the Grundfos "product selection" to see how the power for the pump reduces with flow and pick a good pump. Also you have a pump that was designed to build house pressure, and the Geo only needs 15 PSI. A dual pressure setting with a VFD will get you as energy efficient as you can with an oversized pump. But if you get the chance to change the well pump, installing a smaller one that doesn't build 60 PSI house pressure will greatly decrease energy cost. The well pump can work with a CSV set at say 20 PSI, using a 10/30 pressure switch. Then you can have a small booster jet pump with a CSV and a 40/60 pressure switch. This way the booster only runs a few minutes a day when the house is using water, and the well pump will be very efficient for the geo running at 15-20 PSI. And with both of these pumps using standard pressure switches and simple CSV's, there won't be any "glitches" to worry about. Here is a link to a drawing of a two pump set up like that. http://cyclestopvalves.com/smf/index.php?topic=126.0

Hi David, yes that sounds right. Just use the low voltage supplied in vfd to supply the internal external setpoint relay (which can be set higher than pressure switch), wired in series so when switch closes voltage is supplied back through to vfd enabling higher set point.

I currently use a 5 minute sleep time, so worst case after a geo call or domestic water call it will wait on low rpm (30hz) for 5 minutes before boosting psi and shutting off. In reality there would be no flow at pump during this time so potential to overheat , but motor is idling and hasn't been a problem for me. I had planned to use a run enable to shut down pump after geo call or pressure switch opened but a bug in the vfd caused it to think phmp had stalled and it would cycle pump on and off for several minutes thinking it should still be running but seeing 0hz. The only way I caught this was on my home energy monitor (GEM), I could see weird spikes on pump after geo shut off. I eventually installed a camera to watch the display and external relay to troubleshoot this. The manufacturer told me the firmware logic would have to be fixed/modified and they weren't prepared to do the testing for this release and didn't have further ones planned. They recommended not using run enable and sent me a free flow switch. Anyway, I was disappointed with their support but the product has otherwise been excellent, with a high degree of adjustability. Would probably buy again. Also really like this single pump setup. Nathan

Running 5 minutes at zero flow is not good for the pump. The books say that even with a VFD, a 4" pump in 4" casing needs a minimum of 1.2 GPM flow to stay cool. With 5" casing the minimum flow is 7 GPM. Even at 30hz heat is building in that pump and motor for 5 minutes at the end of every cycle, which I am sure will greatly shorten the life of the pump and motor. It would be rare for a VFD to save enough energy to break even over time, because of the added equipment repairs and maintenance. I have been working with VFD's for about 30 years. Every few years they come out with some new modifications that make me think they may have solved the problems. VFD's have gotten a LOT better over the decades, but they still cannot change the laws of physics, which is what needs to happen to be able to solve all the problems.

Please let us know when you have problems and how much they cost. Because that comes right off the energy savings you are suppose to be getting.

I’m not a pump expert by any means, but after reading valveman’s posts I have a few thoughts:
1) I have a Franklin pump, and the minimum flow table from Franklin shows that 7GPM is for a pump rated between 3-10HP. I couldn’t find any information on a 1HP motor – which is what I have to deal with. Not sure what book Valveman was referring to – again, my own ignorance in this area is showing.
2) Franklin table also states it is for water temperatures up to 86 degrees. Here in southeastern Michigan we deal with water in the 53-degree range. I would image that 53-degree water is more effective at cooling than 86 degree water.
3) It would seem to me that if the motor was rated for some minimum flow that that would be calculated by some formula which would include the amount of heat to dissipate – which has to be a direct function of the power being used. However, it would seem logical (at least to me) that the amount of heat generated using 400 watts would be much less than using 1600 watts (OP’s reported power consumption) – hence decreasing the needed cooling.
4) As previously stated, I currently have a CSV installed. In the case where I have a single shower running consuming around 2GPM the CSV will hold the pump on indefinitely at this flow. So, doesn’t the CSV suffer from the same issue (i.e operating at less than stated cooling of 7GPM flow)? In my case it is probably even worse, as previously stated, my pump consumes pretty much full rated watts regardless of flow, whereas using a VFD would decrease power consumption – in other words less heat to dissipate.
Again, I’m no master pump engineer, and I could be wrong on every count – if I am, so be it. No pride to be bruised! I’m just looking to educate myself.

Cooler water does help. But if there is no flow, the 50 degree water around the motor will boil fairly quickly with 400 watts of heat. Think (4) 100 watt light bulbs in a gallon of water. It will heat up quickly. And yes 400 watts is much less heat than 1600 watts. There are very few brands and sizes of pumps that do not drop in amps when being restricted. With a CSV, the amps only need to drop by 10% to de-rate the motor load enough to safely pump hot water, so it takes very little cool water (86F) flow to prevent overheating. De-rating means it is still a full 1HP motor, it is just pulling .9 HP or less load. When the amps do not reduce, water cooler than 86F helps a lot.

The difference with a VFD is that it is not "de-rating" the motor load, it is "creating" a small motor from a larger one. The motor still needs max cooling flow rate, which by the way is about 0.5 feet per second. This 1/2 fps flow is needed even though the amps are reduced, because the harmonic content of the power created by a VFD adds additional heat.

The same Franklin book that shows 7 GPM is needed for a 4" pump in 5" casing, shows a requirement of 1.2 GPM with a 4" pump in 4" casing. Both of these numbers relate to the 0.5 feet per second flow needed to cool the motor. A VFD should be set to a minimum speed that will produce 7 GPM or 1.2 GPM respectively. Letting a pump just sit and spin at 30hz without moving any water is adding the watt heat to the water, and melting the plastic impellers together at the places where they touch.

Larger horsepower pumps will have a better drop in amps when restricted. But even a 1HP can have a good amp drop. Submersibles use a much larger service factor, so a 1HP pump will draw about 1.4 HP load. If you can find a pump company that publishes the power requirements for their smaller pumps, it is because they make good ones. Here is a link to a power and performance curve for a 16S10 Grundfos. You can see that even at full RPM, this pump drops from 1..4 HP to less than 1/2 HP load. When running a pump at low flow for long periods of time as with a heat pump, it pays to pick a pump that works like the one in this link.

Dave the pump literature calls for a certain linear feet of flow past the outside of pump for cooling, and hence the smaller the diameter of well casing the less actual flow required to produce the desired linear flow around the motor/pump external jacket. At any rate the main issue with pumps as I can tell and have actually experienced is they wear out due to start stop cycles (burned up one starter windings already). The soft-start of VFD should help this.

As for flow restrictions resulting in lower amps, I have yet to see this anywhere. And actual watts consumed are easy to calculate, based on work being done at motor and pump efficiency. I would be interested to see some of the head pressures developed BEFORE the CSV on some high stage pumps, imagine they could easily go into double digits PSI. Can't see how it would change the watts at all if running at 60hz and developing high head pressures.

Nathan

Yes cycling on and off is the main issue that destroys pumps. That is why a Cycle Stop Valve makes pumps last much longer than normal. A lot of people tell me that energy savings on a heat pump is not important at all when the cycling destroys their pump so often. It cost more to maintain the pump system than they could ever save in energy with a heat pump.

A VFD will reduce the cycling, just like a CSV. But the soft start from a VFD is not good for a submersible motor. The longer it takes to get the pump up to 30hz speed, the longer the thrust bearing is running dry. A Kingsbury thrust bearing needs a MINIMUM of 30hz speed to pull the water across the thrust plates. Up to 30hz the thrust pads are running dry. Also resonance frequency vibration happens at several critical speeds. So as the pump slowly ramps up, it is going through every frequency, and several of those cause the pump/motor to vibrate like a tire out of balance.

The backpressure on a CSV is never more than the pump can produce. The CSV just makes the pump think it is in a deeper well when you need it to pump less water. That backpressure can be calculated from the pump curve. It is not an unknown. Even the CSV has a limit of how much backpressure it can handle, and we always check the pump curve to make sure we stay within those limits.

The fact that the power decreases as the flow rate decreases (or head increases) is one of the most misunderstood things about centrifugal pumps. But anyone who reads pump curves on a regular basis knows this is true. See attachment below. The power curve is at the bottom. It shows a 1HP pump with a high service factor pulling 1.4HP at 16 GPM. But where the curve crosses 1 GPM, the pump is only drawing 0.4HP. All pumps do this, some are just better than others. I think it is 2 wire motors that draw more current themselves, as even though the pump curve shows a decrease in HP, they do not drop much in amps. That same pump end on a 3 wire motor will drop amps better. But picking a pump with a good drop in HP is important. Chosen correctly, the amp drop from restricting a full speed pump will be very similar to amps from slowing a pump with a VFD.

Here are a couple links to a video I made of an amp meter on a 1.5HP and a 2HP submersible.
https://www.youtube.com/watch?v=_capz27LiYU
https://www.youtube.com/watch?v=UUtXPzINUXg

Again, just look at the power curve for any standard full speed pump. Pump curves don't lie.

Nathan, maybe a bit off topic but related - what thermostat do you have, and have you determined what is the best way to calibrate between first and second stage, do you do it by stage 1 run-time, or a delta T? I imagine keeping it in first stage, with your listed COPs, as much as possible would be best for energy consumption.

Hey David, it's a Honeywell prestige 2.0 HD. It has setting for Max cycles per hour and controls which stage it's on automatically. All i really care about is not too many start stops on well pump, although vfd softstart kinda protects that way too. Great system! Would do it again

Actually Soft starts are not good for submersible motors. The Thrust bearing runs dry and doesn't have the film of water it needs between the thrust pads and plate until the motor is up to at least 50% speed. The quicker it gets up to speed the better for the thrust bearing. Give it a few years. See how long the VFD system last compared to a regular pump system that could last 30-40 years. If you only get 5 years or so out of the VFD system you have to add in the cost of replacing the pump or VFD about six times.

Good afternoon everyone !
I just jump into the post (my first one here)
I have specific question to choose the good VFD for me.
I have open loop waterfurnace serie 5 with franklin pump 1/2hp 3 wires (very commun i think) the total height is less than 30’ total with water temp less than 55f (montreal area)
I would like to have an VFD because i also have solar panel and i can put the actual pump system on it and it s works very well but it s hard for my batt bank, so if I could save batt capacity it will be very nice
So i looked for PiD10 but the pric is high, i would like something less expensive but not chineese quality too lol
Do you have recommendations ?

Thanks a lot !

With a single phase motor the PID or a Monodrive are about your only options. However, it is just a 1/2 HP pump and it is already working off your inverter. A VFD would give it a sort start, but it won't save any energy and cost more to maintain. If the pump is cycling on and off while the heat pump is running, all you need to do is stop the cycling.

Here we go again......Valveman your valve is not going to stop his pump form cycling....

I am surprised with Montreal having a ground water temp of 55. I live in lower Michigan (Ann Arbor) and our ground temp water temp is 50.

Do you have a way to control the water flow? If you have a valve on your pump I would put a clamp on amp meter on your pump and close the valve. You will see the amps the pump is drawing will go down as you close the valve. The pressure, flow, and pump efficiency is what is in the cost to pump water. So change those to optimize things first.

It appears you are not that far off having a 1/2 HP pump and savings from a vfd might not save you in the long run. If you had a 1 HP pump VFD would help a lot more.

Set the valve so you are wasting minimal water and power while watching the exiting water temp on your unit. I put mine around 35 degrees but I have 2 units in series so 40 might be better for you.

You will also see the geo unit use more energy with the well pump valved closed but not as much as saved by the well pump.

If the pump cycles you will need to add a small bladder tank and maybe separate pressure control switch. I have a check valve that doesn't let the house bladder tank drain down when the geo unit is running.

Good Luck

Here we go again....Newbostonconst my valve does stop pumps from cycling, which is why it is called a Cycle Stop Valve.

The CSV IS the valve that controls the flow from the pump to match the amount being used. You are correct that the amps the pump is drawing will decrease when a valve restricts flow from the pump. As a matter of fact the amps will drop when using a valve to restrict the pump, almost exactly as much as they drop when varying the pump speed with a VFD.

If you had a 1HP pump, a VFD would cause it to waste a lot more energy. The drop in horsepower when using a VFD is not linear with the drop in flow rate. So the more you slow a pump down, the less efficient it is and the fewer gallons per Kwh you are getting.

An additional bladder tank will only reduce the cycling some what. A Cycle Stop Valve stops pump cycling.

Here is what a few people who actually have one and know what they are talking about say.

https://cyclestopvalves.com/pages/reviews

You won't need luck if you do your research!

Posted By Valveman on 19 Mar 2019 02:30 PM
Here we go again....Newbostonconst my valve does stop pumps from cycling, which is why it is called a Cycle Stop Valve.

Compared to a bloken bladder or a wrongly sized one, yes....to a properly sized system...no

All you valve does is make that pump pump at a higher pressure then what your house pressure is set at thus wasting energy and increased run time on the pump.

Your system isn't warranted any longer then a normal bladder system, cost more, and as in the other posts we have had causes the pump to cycle more under normal operating conditions. You are constantly in this same argument with many plumbers on other forums and proven wrong time and time again.