I haven't seen any LED's around yet but I bet they'll show up. I'm planning a house now and rest assured they'll be in mine.

LEDs - no more efficient than fluorescent but far more expensive. Check the lumens per watt.

Why not?


The first thing we noticed was the amp draw or power consumption was virtually the same between VFD and Valve control. It seems the amp draw of a pump will naturally reduce basically the same when restricting a full speed pump with a valve, as when slowing it down with a VFD. So a VFD is just trying to trick a pump into doing something it already does naturally.

Or perhaps a valve salesman was trying to trick you. Power = current x voltage. The VFD changes more than frequency, it also changes voltage. At 30 HZ, or 50% motor speed in the US, a 460 VAC motor will be getting 230 VAC at 30 HZ from the VFD if a constant volts/hertz curve is used. So, since you used the phrase "...as when slowing it down with a VFD..." I can only assume that you are aware that the motor was, in fact, turning slower, which would mean that the voltage at the motor on the VFD is less than the voltage at the motor operating at 60 HZ across the line, so the math is:

Motor A (across the line): Volts = 460 VAC, AMPs = same as VFD motor, power =460 x amps

Motor B (VFD): Volts = something less than 460 VAC, amps = sames as other motor, power = something less than 460 x amps.

Motor B uses less power.


The second thing we discovered was that these systems were running on Valve control most of the time, because the VFD’s were not reliable. The fact that you have bad power in your area should be enough to throw out the entire idea of using a VFD.

I said if you can't program you VCR, these things aren't for you. A VFD, even those twenty years ago, has tremendously more line and motor protection built into it. It will trip and fault more often, however, when a circuit breaker in your service entrance trips we don't consider it to have failed, we clear the overload condition and turn it back on. The same logic works with a VFD. When it trips, it is usually due to one or more of its protection settings. If you know what they mean and how to use them, you get a lot more protection in for your motor control circuit. If you don't know what they mean, you end up saying bad things about VFD's. Also, twenty years ago, many VFD's had only LED/numerical interfaces and were difficult to troubleshoot. Modern VFD's have LCD's with descriptive text displays. They are a lot easier to troubleshoot now, if you buy the right one. They are very reliable if installed and programmed properly.


The power saving theory of a VFD is a myth-understanding. Anytime you reduce the RPM of a pump, you are using more energy per gallon. Forget the cube rule, because you lose head by the square of the speed. So you can’t slow a pump down enough to save energy, or it won’t even get water to the surface, much less build the pressure a house needs.

Have you ever taken a weight on a string and tried to spin it around as fast as your could? Did you notice that a small amount of effort produced a large change in speed at first, but as you spun if faster, you reached a point where a large change in effort produced a very small speed change? Did you notice that you could sense the tension in the string increase the faster you spun it? That's how a centrifugal pump works. If you were to reproduce this experiment you would realize that it only takes about 50% of max effort to get to 80% of max speed. The tension in the string is related to the torque you are generating. The torque requirement increases drastically as you change speed. If you were really perceptive, you might detect the air disturbance, or wind, you generate during this experiment varies linearly with speed. That is somewhat indicative of the flow characteristics of a centrifugal pump.


Look at it this way. A 10 GPM, 1 HP submersible will deliver 10 GPM per horsepower. Reducing the speed with a VFD you might be able to drop the power consumption by half, but the flow rate decreases by 90%. So now you have a 1 HP pump, pulling a ½ HP load and only producing 1 GPM. This means a VFD is causing 500% more energy used per gallon than when the pump is running at full speed.

Your math is completely wrong. However, pressure does fall off as pump speed decreases, and there is a speed at which the pump can not overcome static head. In most retrofit well pump installations I've done, that point almost always seems to be at 45 Hz, or 75% of full speed. You take care of this problem by finding that minimum speed and programming your VFD to use that speed as its minimum. In other words, I typically set them up so that when demand was generated by falling line pressure, the VFD turned on and accelerated to 45 Hz. It would increase from there if 45 Hz motor speed didn't meet setpoint pressure.



n the last 20 years we have made a successful business replacing VFD’s with Valves. It usually takes about 3 to 5 years, after several pump and VFD replacements, before a pump installer or the owner of a VFD realizes the mistake they made.

You have an ignorant customer base.

VFD's die from heat and dirt. Many well pump applications are outside in hot and dirty locations. They absolutely will not last forever in that environment, which is why I tell people to put them in conditioned space if it is at all possible. If you can't, go up a couple of sizes, then the VFD can get rid of more heat.


VFD’s provide “planned obsolescence” for the manufacturers. VFD’s are expensive equipment, that don’t last very long, are not repairable, and are hard on motors.

VFD's have a lot of electronics in them switching high current loads at typical switching speeds of 4000 times a second. Most will switch three times faster, but that is typical. These components will absolutely wear out at some point, but that point is fairly indefinite. These days, VFD's are typically "throw away" designs below 25 HP or so, meaning the power components aren't serviceable. Above 25 HP or so, depending on manufacturer, the individual components are serviceable. In 2003 I replaced a 100 HP VFD that had been in service in an office building on an air handler since 1984. Original motor, also.

In 1992 or so NEMA released a motor spec to make motors more compatible with VFD's, which mainly consisted of upgraded wiring. I think it is called MG2. Motors are often labled "inverter duty" for this reason. If your motor leads are over about 200 feet long, which they could be for a well, you have to use something called a dv/dt filter, or you will shorten motor life. Before the 1992 spec change, it was hit and miss on getting these things right.


So a constant pressure valve is a good alternative to the VFD.

What does one of your valves cost? What's the life on the packing? What about the actuator? I've had more customers switch to VFD's to get away from control valves than to save power.



However I am still amazed at how many people do not believe that companies would do things like design in a short fail date for their equipment.

Well, take a look at these boards, the SIP guys say the ICF guys are all wrong and the stick built guys say the ICF and SIP guys are snake oil salesmen and the spray foam guys say the cellulose guys are full of it, too. I can assure you that no manufacturer of industrial equipment, even the people you represent, have any interest in selling product that has any kind of planned obsolescence in it. You have to remember that very few manufacturers actually make everything that goes into their product. VFD manufacturers, for instance, by diodes, capacitors, resistors, IGBTS, and numerous other electronic components. There are only about five manufacturers of IGBT's in the world, all of the 120 or so brands of VFD's in the world use IGBT's from those guys, three or so of which could be in a fallout zone in Japan as we speak. No manufacturer is interested in sending a product anywhere in the world with faulty components. They are, however, interested in meeting industry expectations at a competitive price, just like any builder on this site is.

And one more point:

If VFD's are so unreliable, and if the energy savings don't work, what lead practically EVERY Asian air conditioner manufacturer to use them?

(Please note that in the HVAC application the compressors are positive displacement so the energy savings are only linear, but obviously......they are there)

 

“Or perhaps a valve salesman was trying to trick you. Power = current x voltage. The VFD changes more than frequency, it also changes voltage. At 30 HZ, or 50% motor speed in the US, a 460 VAC motor will be getting 230 VAC at 30 HZ from the VFD if a constant volts/hertz curve is used.”

No, just trying to keep VFD salesmen from pulling this trick.  Why would you bring up 30 HZ when as you said, 45 HZ is as low as you have ever been able to run a pump and maintain pressure?  Even then I think you have oversized the pump to be able to reduce the speed to 45 HZ.  This is the reason over sizing the pump is typical when using a VFD.   50 HZ is the lowest I have ever been able to run a correctly sized pump and still maintain the pressure required.  More importantly, we are not talking about the energy needed to spin the motor.  We are talking about the energy used to power the pump.  No mater the volts/hertz ratio or the amp draw of Motor A or Motor B, the pump is what determines the load.

 

“It will trip and fault more often.”  Or..

“They are very reliable if installed and programmed properly.”

Which is it?  You can’t have it both ways. 

 

“You get a lot more protection in for your motor control circuit.” 

A VFD is the only reason you need more protection for your motor control circuit.   A properly controlled pump system without a VFD shouldn’t cause a fault of any kind.  Any legitimate fault is too late, because it just means you didn’t get something right.  And the more “protection” you have in a motor controller, just means more nuisance trips and a mad customer.

 

“Also, twenty years ago, many VFD's had only LED/numerical interfaces and were difficult to troubleshoot.”

Just because I was dealing with VFD’s over 20 years ago, doesn’t mean I haven’t kept up with the technology.  I buy the latest and greatest VFD every couple of years to play with.  And yes the newer designs are easier to program and troubleshoot, but they still haven’t solved the problems of harmonics, voltages spikes, resonance frequencies, bearing currents, and all the things Mother Nature won’t allow to be changed.

 

“Your math is completely wrong.”

I disagree!  Lets use your exaggerated 45 hertz minimum speed for an example.  You said it takes a minimum of 45 hz or 75% speed to lift water to the top of the well and produce the pressure required.  Power required drops off by the cube of the speed. Which means at 45 hz you still need 42% of power to pump even 1 GPM.  If at full speed a 1 HP pump produces 10 GPM, then reducing the speed to 45 hz with a VFD delivers only 1 GPM.   At 45 hz and 1 GPM, the pump is drawing .42 HP, which means the VFD is causing 420% more energy used per gallon produced.   A 100 GPM, 10 HP slowed to 10 GPM, or a 1000 GPM, 100 HP slowed to produce 100 GPM are still using 4 times more energy per gallon.  This is typical of a VFD controlled pump at any volume and/or pressure required.  Most people just see the amps or watts drop off to 42% and think the VFD is saving energy.  They are shocked when they finally realize that reducing the power to spin the pump by 58%, is actually increasing the cost per gallon by 400%.

 

“You have an ignorant customer base.”
”VFD's die from heat and dirt. Many well pump applications are outside in hot and dirty locations. They absolutely will not last forever in that environment, which is why I tell people to put them in conditioned space if it is at all possible.”

Really?  You don’t want to go there!  The customer base is not ignorant, they were just myth-informed about VFD’s.  I agree the only VFD’s I have seen that lasted anytime at all, were installed in a dust free, air-conditioned room, with a full time maintenance man.  Even in a clean room an air-conditioner filter will stop up with lint, and so will the screen and fan on a VFD.  As you said “heat and dirt (lint) will destroy the VFD”.  And if you forget to clean the lint from the little filter, it gets destroyed much sooner.  As a side note, how much extra energy does it take to heat and cool the room for the VFD?  I know of a golf course with VFD controlled pumps, where the air conditioners for the pump room, use more energy than the pumps themselves.

 

“VFD's have a lot of electronics in them switching high current loads at typical switching speeds of 4000 times a second. Most will switch three times faster, but that is typical. These components will absolutely wear out at some point, but that point is fairly indefinite. These days, VFD's are typically "throw away" designs below 25 HP or so, meaning the power components aren't serviceable. Above 25 HP or so, depending on manufacturer, the individual components are serviceable. In 2003 I replaced a 100 HP VFD that had been in service in an office building on an air handler since 1984. Original motor, also.”

Newer VFD’s have considerably faster switching than older VFD’s.  The faster the switching, the more heat they generate.  The faster the switching, the faster the rise in voltage.  The faster the switching, the shorter the time between voltage spikes.  None of these things are good for the motor.  “Throw away” is what they want you to do to all VFD’s in a short period of time, so they get to sell you another one.  Even larger VFD’s are cutting corners to better price compete.  The older VFD’s had a power pack for each phase and lasted longer.  Newer VFD’s have a single power pack.  Cheaper, not repairable, don’t last very long.  See a pattern here?

 

“In 1992 or so NEMA released a motor spec to make motors more compatible with VFD's, which mainly consisted of upgraded wiring. I think it is called MG2. Motors are often labled "inverter duty" for this reason. If your motor leads are over about 200 feet long, which they could be for a well, you have to use something called a dv/dt filter, or you will shorten motor life. Before the 1992 spec change, it was hit and miss on getting these things right.”

Translation;  Motors being produced with 600 volt insulation would not stand the spikes of 2,000 volts or more coming from the VFD’s.  So they changed to 2,000 volt insulation for all motors.  They also had to eliminate air gaps turn to turn in the windings, as well as rap, tie, and support the windings better to handle the harmonics, noise, and vibration from VFD control.  “Inverter duty” just means they had to make motors much stronger to withstand the abuse of VFD controls.  Many motors are even labeled, “Inverter Duty, Voltage Spike Resistant”.  I wonder where these voltage spikes are coming from?

 

Some manufacturers are adding the line or load filters as standard equipment, to be able to hit more than miss, because they don’t know how long the motor leads will be.  Another side note; dv/dt filters have considerable heat or power loss, and reduce the efficiency even more.

 

And I should also mention they haven’t figure a good way to handle bearing currents.

 

“What does one of your valves cost? What's the life on the packing? What about the actuator? I've had more customers switch to VFD's to get away from control valves than to save power.”

I am not trying to advertise a valve here.  However, a valve cost a fraction of the price of a VFD.  There have been some new innovations that have eliminated the problems associated with old style pump control valves.  There is no packing, needle valves, screens, or even a seat to wear.  New technology does not have to be electronic to be beneficial. 

 

“I can assure you that no manufacturer of industrial equipment, even the people you represent, have any interest in selling product that has any kind of planned obsolescence in it.”

You are the perfect customer!  Boy have I got a deal for you on some land in New Orleans!! 

 

“No manufacturer is interested in sending a product anywhere in the world with faulty components.”

I didn’t say faulty!  I said a planned life expectancy, which is a major consideration for manufacturing almost any product these days.  Although it is only discussed in very high level corporate meetings.  Nobody else in the factory knows anything about it.  Just like everybody using sealed bearings these days.  You can buy a 20,000 or a 50,000 hour bearing.  An occasional shot of grease would make a bearing last forever, which is why you can’t get a good grease-able bearing for most things anymore.  Everything, and I mean everything you buy, the manufacturer already knows exactly when you will be back for a replacement.  Don’t kid yourself!  “Manufacturers being interested in meeting industry expectations at a competitive price” is one reason they put even less quality into their products.  Another reason is so they can “charge a competitive price” over and over again.

 

“If VFD's are so unreliable, and if the energy savings don't work, what lead practically EVERY Asian air conditioner manufacturer to use them?”

I don’t know about air conditioners.  I am only talking about controlling centrifugal pumps that must always produce a certain head.  There are some good applications for a VFD, and a compressor maybe one of them.  But I hope they have done the math, and don’t just think slowing the RPM of a motor will always save energy.

Point by point arguments get very tiresome, but:

Why would you bring up 30 HZ when as you said, 45 HZ is as low as you have ever been able to run a pump and maintain pressure?

I used 30 HZ to illustrate the point and make the number easy to understand. 30 is half of 60, 230 is half of 460. If I had used 48.5 Hz as an example, the point wouldn't be as easy to see, but, clearly, it wasn't easy enough for you.

I said In most retrofit well pump installations I've done, that point almost always seems to be at 45 Hz, or 75% of full speed. Two things should be obvious: if it is a retrofit, I didn't size the pump and I never said 45 Hz was the lowest speed I was able to pump and maintain pressure.

50 HZ is the lowest I have ever been able to run a correctly sized pump and still maintain the pressure required. In which case I would set minimum frequency on the VFD at 50 Hz or slightly higher. Big deal. Most of the retrofits I have done started pumping meaningful volume at 45 Hz or so. I used the word "seems" to imply a little bit of variability there. It could be that your definition of "correctly sized" is different than the one the pump guys I worked with used.

More importantly, we are not talking about the energy needed to spin the motor. We are talking about the energy used to power the pump. No mater the volts/hertz ratio or the amp draw of Motor A or Motor B, the pump is what determines the load.

First off, ENERGY and Power are two different things, but I know what you mean. Did you have a point with this? How can the energy used to spin the motor be appreciably different than the energy used to power the pump, other than an adjustment for motor efficiency? The load characteristics on the motor are going to mostly match the load characteristics of the thing it is attached to, every time.

I use the term "mostly match" because I am going to continue to express load in terms of amps. If we were theoretical purists, we would discuss it in terms of torque, which would mean that we would have to subtract the amount of current that is magnetizing the motor windings and not inducing torque to the rotor. Amps suffices as load for this conversation.

Which is it? You can’t have it both ways.

Do you have ground fault receptacles in your bathroom? They trip more often than standard receptacles. Do you consider that a failure. Do you throw away your computer every time it hangs up, or do you clear the problem condition and restart it. A VFD has protections in it and programmable responses to those protections. By default, VFD's are factory programmed to shut down and require a manual reset to those trip conditions. Do you know why? It is because the VFD manufacturer does not control the installation condition. Since you might put your VFD on a piece of rotating equipment, and, if the power blinks, for instance, and unsuspecting person might reach into that piece of equipment thinking it was stopped. If the VFD were to automatically start running when power was restored, that person could be seriously injured. For this reason, factory default settings on a VFD are to stop the VFD by removing the run command fully. Then, when the run command is removed, reset the error. Once the error is reset, restore the run command. This is basic safe operation.

It's not a problem in most pump installations, so you change those settings. I typically set it to automatically restart on power up if the run command is present. I also set it to delay ten seconds or so after a fault, automatically reset the fault, and run on fault reset if a run command is present. Over and above that, I adjust all the trip responses to my actual site conditions. For instance, on a pump, I can use a function called stall prevention, rather than an over current trip (not to be confused with thermal overload, which is your primary motor protection). You can tailor trip behavior to the needs of your actual conditions. If you leave it at factory defaults, as most people do, you are going to get a lot of nuisance trips. This is the part that takes someone experienced with VFD's and the application, and one of the reasons I said earlier that they aren't for everyone.

But, make no mistake about it, a VFD will trip more than a standard across the line starter because it can detect tremendously more potentially damaging conditions. If you know what it is trying to tell you, you can make the VFD very reliable. When it trips, it is trying to protect itself or the motor based on 100's of user selectable data points. When an across the line starter trips, it is tripping because a small, bimetallic chunk elongated enough to break a circuit.


And yes the newer designs are easier to program and troubleshoot, but they still haven’t solved the problems of harmonics, voltages spikes, resonance frequencies, bearing currents, and all the things Mother Nature won’t allow to be changed.

Harmonics: use active front end ($$$), harmonic filter($$), or line reactor($), or if your VFD is smaller than ten percent of your load, do nothing.
Voltage spikes: That's really a line problem, not a VFD problem. It does happen though. A true high line voltage will damage even a motor on a conventional starter. A VFD will trip on high DC Bus voltage if line voltage goes high long enough. Active front end won't. A conventional VFD will fault, but you can use a contactor to break the line on a high DC buss voltage fault.
Resonance Frequencies: If you are talking about a harmonic resonance on the electrical line, it's really addressed by power distribution system design or the things listed under harmonics. If you are talking about resonant frequencies related to mechanical vibrations in the mechanical systems, it's addressed by a programmable function usually called "jump frequency". You program your VFD so that it won't run at certain frequencies that create mechanical resonances.

Bearing currents: depends on motor lead length and is addressed by the MG2 spec I mentioned earlier. Each VFD manufacturer releases specs on lead length and output line filter requirements. Typically, no issue on 230 VAC motors with lead length less than 400 ft, no issue on 460 VAC motors with lead length less than 200 ft. Bearing current issues within those lead lengths are ofter the result of grounding issues at the motor. DV/DT filter required over those lead lengths.


Power required drops off by the cube of the speed. Which means at 45 hz you still need 42% of power to pump even 1 GPM. If at full speed a 1 HP pump produces 10 GPM, then reducing the speed to 45 hz with a VFD delivers only 1 GPM. At 45 hz and 1 GPM, the pump is drawing .42 HP, which means the VFD is causing 420% more energy used per gallon produced. A 100 GPM, 10 HP slowed to 10 GPM, or a 1000 GPM, 100 HP slowed to produce 100 GPM are still using 4 times more energy per gallon.

In a centrifugal pump, power increases as the cube of speed and pressure increases as the square of speed and flow increases linearly with speed. If a pump will flow 10 GPM at 60 HZ, then it will flow 7.5 GPM at 45 HZ, but it will be at 56% of the 60 HZ pressure. If this is enough to overcome static and dynamic head on a well pump, you will get 7.5 GPM on a theoretically perfect pump. Of course, in reality, dynamic head changes in accordance with how much water we are actually forcing through that pipe, and you have to remember that our conventional means of demand modulation is to open and close mechanical valves which also increase and decrease head, so real world results are a little different, i.e., we are typically inducing more head by closing valves to get that VFD to slow down to 45 HZ in the first place (the VFD is typically responding to a pressure transducer in the line) so when we induce more head by restricting the line with a valve, we will not see that flow at 45 HZ.

A better test would be to open all the valves and use a flow meter as feedback to the VFD, and determine our flow, motor speed, and power at the point the pump overcomes static head and at speeds greater. Of course, your valve can't be used on this test because it works by increasing head to decrease flow.


Newer VFD’s have considerably faster switching than older VFD’s. The faster the switching, the more heat they generate. The faster the switching, the faster the rise in voltage. The faster the switching, the shorter the time between voltage spikes. None of these things are good for the motor. “Throw away” is what they want you to do to all VFD’s in a short period of time, so they get to sell you another one. Even larger VFD’s are cutting corners to better price compete. The older VFD’s had a power pack for each phase and lasted longer. Newer VFD’s have a single power pack. Cheaper, not repairable, don’t last very long. See a pattern here?

A standard switching frequency is 4000 HZ on small motors and 2000 HZ on larger motors. The only significant reason to go faster than that is to reduce audible noise. This has been true for a long time. Newer VFD's do not switch faster than older ones, at least not for the last 15 years or so, because there hasn't been any significant performance benefit from doing so. Yes, faster switching increases the reflected wave phenomena, which are the spikes on the output side you keep mentioning. The single power pack you mention is the availability of the power electronics in a unitized package. It cost less and is more reliable, and cuts down on the possible manufacturing errors, but if it pops it is not repairable. Control boards, cooling fans, capacitors, and other components remain serviceable. Thirty years ago, there were entire businesses based on repairing televisions. They are gone now, because TV's are no longer serviceable. The reason is because all of their electronic components are similarly unitized. The result for me is that I have only owned one TV for the last 25 years until I bought an LCD this year. Things change. When I was a kid I could buy parts to fix the alternator on my car. I'm sure you can't buy those anymore, either. Things change.

You are the perfect customer! Boy have I got a deal for you on some land in New Orleans!!

I stand by my original statement. No one I have ever worked for had any interest in putting bad equipment in the field. Warranty costs are massive, and losing a major customer is a killer.

Enough of this. I can make a VFD work and a customer will be satisfied with it on a good application, and one of the best is a centrifugal pump, but they aren't for everyone, just like some people can't use computers or satellite TV.

Birdman:

My 2 cents, esp. re. 20-25 mph wind "days on end"

Since you are in on the 'rules and regulations' end of the local gov., how about removing any local restrictions on small scale wind turbines? Betcha got LOTS of restrictive codes out there on the is., eh?

Betcha a local enterprenuer could soon be selling small 10 ft 2kW (at 25 mph) like hotcakes if there were no restrictive building codes to inhibit useage.
1 day at 40 cents = $19.20. Say 25% of the time you have wind, then ROI at a 5% interest rates would support a $30K initial cost. DIY costs for a 2 kW turbine could be as low as $1K total. Had a friend in OK built his own back in the early 80's for under $300 out of pocket, using surplus drill pipe for the tower (biggest cost) and a generator salvaged off a gas gen-set with a trashed engine and a scrapped Cessna prop + a fiar amount of his own time.

Folks up along the western Scottish and English coast are relatively poor judging from the homes, but a very large percentage have small turbines spinning. Took the train from Carlisle to Barrow last year and saw lots of them, many as small as 3-4 ft dia just producing a few hundred watts, but still a quick payoff.

Junkhound,
That's a hot topic. Zoning is very restrictive now due to an early tower collapse and view and noise issues. We are all over easing the restrictions. The conventional thinking is that we would be better off with several utility scale turbines than several hundred residential scale units. This is a town that lives on summer tourism and our viewsheds are our lifeblood. This is a long ongoing debate - but I hear what you're saying. I'd be wary of DIY units due to the survivabiilty issues. Unit should be able to survive 120+ mph.

As a tourist, I consider it a plus when I see an area or building using renewable energy.

JonR - Me too. But that makes us unusual.

I would love to see our little island become like Samso in Denmark - a model of sustainable energy and self sufficiency. We're working on it, but not every one adopts at the same pace....

Theoretically you should be able to get 7.5 GPM form a 10 GPM pump when running at 45 hz.  However, there is a minimum speed that will produce the total head required at any flow rate.  Once you reach this minimum speed, flow is basically determined by how many faucets you have on.  But the speed can’t be reduced anymore and still produce the head required.  So the speed is still at 45 hz as the flow from the faucets vary from 7.5 GPM to 1 GPM.  And at 45 hz and 1 GPM you are using 400% more energy per gallon.  If you want to say a VFD gives you lots of parameters and alternatives, and for knowing how to install and program one, you can charge a premium for your work, then I would agree.  But furthering the myth that a VFD saves energy is not beneficial to anyone.

 

“Enough of this. I can make a VFD work and a customer will be satisfied with it on a good application, and one of the best is a centrifugal pump, but they aren't for everyone, just like some people can't use computers or satellite TV.”

Sure you can make it work.  The question here is does a VFD save energy and the answer is NO.  When efficiency is the only consideration, sizing the pump to the exact requirement is best.  When that is not possible, pumping at best efficiency into an elevated or large pressure tank is the next best option.  A soft start can reduce end rush currents and help start the pump with a smaller generator.  Even then I prefer an Auto-Transformer soft starter over the electronic type. 

 

In my opinion, if a customer has to be smart enough to use a computer or satellite TV to be happy with a VFD, then no customer should have one.  People with water systems want to be able to turn on the faucet when they want water, and turn off the faucet when they don’t, nothing else.  If water doesn’t come out of the faucet every time, or they have to punch one reset button, the installer has failed to provide a reliable system.

I don't expect to change your mind, but you keep posting things that set off red flags to me.

However, there is a minimum speed that will produce the total head required at any flow rate. Once you reach this minimum speed, flow is basically determined by how many faucets you have on. But the speed can’t be reduced anymore and still produce the head required. So the speed is still at 45 hz as the flow from the faucets vary from 7.5 GPM to 1 GPM. And at 45 hz and 1 GPM you are using 400% more energy per gallon. If you want to say a VFD gives you lots of parameters and alternatives, and for knowing how to install and program one, you can charge a premium for your work, then I would agree. But furthering the myth that a VFD saves energy is not beneficial to anyone.

I run my well pump VFD's in PID mode with a pressure setpoint. Feedback is provided by a pressure transducer in the line. The VFD runs at the speed required to meet the pressure setpoint. So, in your example of opening faucets, the flow will not reduce as more faucets are opened because the VFD increases speed to satisfy the pressure setpoint. I use a feature called PID sleep, which means once the pressure setpoint is satisfied and the VFD reduces speed to maintain setpoint as faucets are closed, it will eventually drop below a frequency threshold, called the sleep frequency, where the VFD will shut off. If pressure drops, the VFD "wakes up" and pumps at whatever speed is required to maintain line pressure. With all valves closed, the minimum frequency that was required to pressurize the lines (satisfy the pressure setpoint) was often approximately 45 HZ, though sometimes it was more than that, but not much. The PID sleep frequency works best a little above that, 50 HZ worked well on most of the well pumps, because it made a solid "bump", so to speak in pressure, which induced a little hysteresis to the system to compensate for the inevitable leak down.

There was never a pumping installation on a well pump that didn't use PID control with pressure feedback, also I put VFD's on building water pressure boosters using the same setup, PID control with pressure feedback. The situation you are describing, a VFD operating at a fixed frequency regardless of flow demand, is not a control scheme I have ever been asked to work with, and I don't see why anyone would want to do that.

The question here is does a VFD save energy and the answer is NO

Whatever. As noted, many people disagree, including the college professors I had.


When efficiency is the only consideration, sizing the pump to the exact requirement is best.

So, in your example of someone opening multiple faucets, just exactly what method do you use to size the pump to the exact requirements? How can you possibly size a pump to the exact requirement of one faucet, and then it still be sized correctly when two are open at the same time?


People with water systems want to be able to turn on the faucet when they want water, and turn off the faucet when they don’t, nothing else. If water doesn’t come out of the faucet every time, or they have to punch one reset button, the installer has failed to provide a reliable system.

Well, a person who never wants to have to punch a reset button won't be happy with an across the line well pump, either, so he'd probably best stay in the city and work for the We Say So Corporation.

Good luck.

Sounds as if potable water is a challenge also - how about gray water recycling systems? Rainwater storage?

-Rosalinda

I am sorry.  I must not be good at describing things for you to have gotten so far off the subject, and to think you need to explain the basics of how a VFD works. 

 

I have been teaching classes on this subject for almost 20 years, which was long before sleep mode. I use to harp on the problems of always having to maintain the constant pressure setting of the PID loop.  So I wonder where they got the idea of sleep mode?  I should have kept quite about that.  Anyway, you still don’t understanding the minimum speed thing.  You are seeing it happen here… “The PID sleep frequency works best a little above that (45HZ), 50 HZ worked well on most of the well pumps.”  You just don’t realize what you are seeing.  If you set the minimum frequency at 45 HZ, the pump can’t go into sleep mode, because it can’t get down to that speed and supply the head and pressure required (satisfy PID setting) at any flow rate.  The minimum speed that the pump can operate and still produce the head required is more than 45 HZ.  This is true, even if there is only a 1GPM faucet open, and is also why you have to set the sleep mode up to 50 HZ.

 

Head dropping off by the square of the speed is the most important part of the Affinity law.  Horsepower reducing by the cube of the speed, or flow by a one to one ratio, are of no importance, if the pump isn’t spinning fast enough to lift water to the top of the well.  So you can’t slow the pump down by 25% to get 25% less flow.  You can only slow the pump down by 25% and still get water to the top of the well and produce the pressure required.  Then because you can only slow the pump down to 45 HZ (25%), the flow is determined by how many faucets you have on.  And if you only have a 1 GPM faucet on, you are only getting 1 GPM at 45 HZ, which is 420% more energy used per gallon.

 

If you, your professors, and other engineers are confused about this issue, I can just imagine how confusing it is for the average person.  I know there are lots of pump and VFD engineers who know this is a myth.  But hey, why should they explain it to us when they are making a ton of money on VFD’s, by letting the rest of us wallow in our ignorance of thinking a VFD saves energy.

 

“I don't expect to change your mind, but you keep posting things that set off red flags to me.”

LOL!  No, you will never convince me that fiction is fact.  You might as well try to convince me driving faster will give better gas mileage, as to say a VFD will save energy.  I know both of these things to be false.  There is no grey area here.  This is basic pump knowledge.  Get out some pump curves and do a little studying.  Then you can go back and teach your professors a thing or two. 

 

Everybody, including professors, see the amps drop by 50% to 60% and thinks a VFD is saving energy.  Using less energy to spin the pump is not the goal.  Using less energy per gallon of water produced is the goal.  Spinning the pump slower to save energy is like driving faster to save gas. It just doesn’t work.  I don’t know how to make this any more clear.

 

The question here is does a VFD save energy and the answer is NO

”Whatever. As noted, many people disagree, including the college professors I had.”

Some people will get out the pump curves, start looking at things from the minimum possible speed perspective, and have an eye opening experience.  Others just say, “my professor told me this, so it must be true”, and continue to live in Lala Land.

 

So, in your example of someone opening multiple faucets, just exactly what method do you use to size the pump to the exact requirements?

That is not possible!  That is why I said you need an elevated or large pressure tank to stay at the best efficiency point.

 

”Well, a person who never wants to have to punch a reset button won't be happy with an across the line well pump either”

I disagree!  An across the line starter, controlling a properly designed pump system, running on sinusoidal AC power (without a VFD), should never cause a nuisance trip.  Pump systems should even come back on by themselves after a power outage, without resetting anything.  I have a personal well pump system that hasn’t been touched since installed in 1982.  All of my customers expect and deserve this kind of dependability.  You can’t get that kind of dependability with a VFD, and a VFD doesn’t save energy.

To put the issue in perspective, the total electricity bill for typical residential well water pumping is what - < $50/year? Perhaps $300/year if geothermal is being used.

Posted By jonr on 19 Mar 2011 11:06 AM

To put the issue in perspective, the total electricity bill for typical residential well water pumping is what - < $50/year? Perhaps $300/year if geothermal is being used.

Agreed!!  That would be for an efficient (non VFD) system.  With a VFD that easily turns into $200 a year for residential and $900 a year for a heat pump.

OK. Since I started this thread I'm now going officially on record - "I'm sorry I asked!"

I think both Tigerfan6 and Valveman would agree that there is NO COMPELLING PUBLIC POLICY reason here to REQUIRE BY LAW that VFD's be installed with new or replacement well pumps. So my initial question was answered. Thanks!

NO COMPELLING PUBLIC POLICY reason here to REQUIRE BY LAW that VFD's be installed with new or replacement well pumps


Well said, your are CORRECT!!

Just to 'enter the fray' on vfd, FWIW, my own well pump is VSD - in the PWM (pulse width modulated) sense. AVERAGE speed is maybe about 340 RPM . How does it work so low? Aha, the magic of PWM, the pump spins at 3400 rpm till the pressure switch turns it off, then it is off for 9/10 of the time, then the low pressure turns it back on, and it is on 1/10 or the time. The resulting 0.002Hz PWM is slower rate PWM than the 4 kHz mentioned earlier for VFD, but still 'PWM' and VSD, though not VFD, heh, heh.

Thus, here is another arrow for your quiver to support you final decision: out on Birdman Island, EVERYBODY is ALREADY using 'variable speed' to get good overall efficiency, so why throw another meaningless government regulation into the mix, whose only beneficiary would be those selling VFD. Query: was the original call for a 'law' promulgated by a 'seller'??

Apparently this CSV vs VFD "debate" has gone on elsewhere, with no consensus there either. According to this site:

http://forum.geoexchange.org/open-loop/570-cycle-stop-valve-2.html

Valveman is the owner of the company that makes the CSV, so that his input to the discussion might be considered biased. Whether technically his arguments are right or wrong seems no more resolved on that site than on here.

If there is a an energy savings for one particular pump/control arrangement over another I'm satisfied it is insufficient in magnitude to justify requiring it by law or regulation. With such a small difference in energy use, other factors can reasonably sway the decision for one system over another and still be environmentally responsible.

Junkhound:
The inquiry into whether to regulate this or not was ABSOLUTELY NOT initiated (or even pressed for once initiated) by ANY commercial interest one way or another. I'm glad you asked the question so I can be really clear on that - excellent point. The committee I am a member of is trying very hard, and with the purest of intentions, to craft an energy policy for our little island. We find ourselves at the bleeding edge of energy issues due to our isolation and high costs, our dependence on tourism, our dedication to natural conservation and environmentalism, the possibility of hosting the first US offshore windfarm and the interrelationship of all of those issues with our economy and Climate Change (island communities are very sensitive to this with respect to seal level changes). Many here (but certainly not all) look to the island of Samso in Denmark as a model.