Help Needed from Any Scala2 or VFD Experts

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HOOS1990

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I have a SCALA2 pump, newly installed, that at certain times will cycle on and off constantly while a tap is open. Essentially what happens is that while a tap is open the pump gets the pressure up to to the set point (70 psi), cuts off, pressure drops to around 60, then the pump kicks back on and it does that all over again. This video (not made by me) is exactly what I am seeing:

At other times, the thing runs like a champ. I open a tap and it runs until the tap is closed. I open another tap and it seamlessly keeps the pressure constant. Another tap, again, seamless. I've had 5 taps open at once all at 70psi, so when it works its pretty cool.

I'll add that I have read the forums and understand there is some difference of opinion on VFDs and grundfos pumps. But, I've got the SCALA2 installed and would like to try to make it work. I have 10 more days to return it for a full refund, so if I cannot get it to work properly i will uninstall and perhaps go with a CSV type solution.

Questions:

1. Does anyone know what causes this issue?
2. Could it be the internal pressure tank? It is precharged at the factory to 18.5 psi. Anyone know what it should be set to for incoming pressure of 40 and outgoing of 70?
3. Could this be caused by fluctuating incoming pressure. I do notice that sometimes my incoming pressure is 40, others its 45, sometimes even 50. I am wondering if adding a pressure reducing valve to the supply side to keep the pressure at 40 (maybe even set it to 35) might resolve the issue?

Thanks!
 

Reach4

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HOOS1990

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Valveman

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There is a lot of sales information on that pump, but very little on technical instructions. I see where others who had that same problem added some air to the tank, and it seemed to help some. It doesn't sound like the variable speed part is working at all. With other Grundfos products like the SQE, when the pressure transducer fails the pump reverts to cycling on and off as if it had a regular pressure switch. That maybe your problem here. But I don't see that symptom in any of the instructions.

There sure are lots of problems discussed in the reviews of this product for it not to even be a year old. But hey it only cost 600-700 bucks, so just replace it every few months when it starts acting up. That is the exact goal of the manufacturer. They don't make any money on pumps that last 30 years. They made it real easy to just remove the old one and install another one.


As with any variable speed pump, there is so much electronics in the controls, you could have many different problems. Grundfos still makes some good pumps like the JP series jet pump. The JP series doesn't have any electronics except for the old reliable 40/60 pressure switch. Adding a simple mechanical (no electronics) Cycle Stop Valve can make the JP series deliver the same constant pressure as a variable speed type pump. Keeping it simple and mechanical (no electronics) is the best way to get 30 years out of a pump like that.

Grundfos is one of many pump companies who tries to build a Variable Speed Drive directly into their pump, so you won't have any choice over how it is controlled. This way you can just budget maybe 50 bucks a month for the rest of your life to cover the replacement pumps.
 

HOOS1990

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thanks for the replies so far. I increased the tank pressure to 49 psi. That seemed to have solved the problem. But this morning, I noticed in running the sink that the pressure was fluctuating. I went to look at the pump and it was cycling on and off. Took the pump out of the loop and checked the incoming pressure. 60 PSI. Never have seen it that high, typically its around 40. So, my thought is that when the incoming pressure and outgoing set points are close (I have the Scala set to maintain 70), the pump has a hard time figuring out what to do. Sure enough, I raised the setpoint to 80, and the pump ran fine, no cycling.

I'l keep an eye on it when the city pressure drops again and see if the pump runs fine. In the meanwhile, looks like I'll be ordering a PRV to deal with the city water incoming pressure fluctuations.
 

Valveman

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Glad you got it working. I started working with VFD's over 30 years ago. I haven't had a chance to play with one of those models yet, but I don't know why high incoming pressure would cause a problem. It is a shame you have to use a simple mechanical pressure reducing valve to make all that high tech stuff work. I think you will discover in a short time that the simpler and more mechanical you make your pump system, the less likely you will be out of water, and the less it will cost you.

A CSV works similar to that simple mechanical pressure reducing valve. The difference is you put the CSV on the discharge of the pump instead of the inlet, and it makes a constant pressure system without any of the high tech electronics that makes pump systems expensive and less dependable.
 

phil Tuttobene

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I would NOT run your pressure to 80 PSI. Most fixtures are only rated to 80. So surges may reduce the life of fixtures, especially toilet valves.
If your pressure is 60 coming in, I question the need of a booster. Typical house pressure should be 60-70PSI but no higher.

If your water supply can not keep up with demand the pump will cavitate. This is where a well designed VFD controlled pump comes in.
A well designed variable speed pump will automatically detect cavitation and modulate its speed to the point that cavitation just stops.
Once the demand falls below the GPM your supply can furnish the pressure automatically rises back to the setpoint.

Be careful with cavitation, it will destroy the pump. I have written many articles on designing anti-cavitation algorithms and its a very big part of a well designed variable speed pump.

Hope it helps.
Phil
 

Valveman

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rsgard:
I was wondering how your new pump was working? Although it is true that most pump companies are reducing costs and building in obsolescence, not all companies follow this trend. There are engineering companies and there are "sales companies". Engineering companies have a passion for what they build, constantly improve and always striving towards perfection. They put quality and PR ahead of profit.

As a VFD consultant with over 40 years experience I get a bit disappointed when I hear about people that purchase a VFD controlled pump that is not built to last and more disappointed when I hear people say this is the norm. I can assure you it is NOT.

In a meeting last week with a long time Grundfos marketing manager, now working for a competitor, I shared my views with why the Grundfos Scalia2 is so problematic. Customers have given me their units to tear into and inspect. Of course they knew before hand that the pumps would never be usable again. Due to this inspection we came up with some clues to their problems and this helped me build better alternatives.

1) The Scalia uses a magnetic pin wheel to detect flow. Its embedded in the pump and it gets plugged up easily with Teflon tape, minerals or any contaminants in the water. When it fails, the pump fails and it's not serviceable.
2) The Scalia uses a bladder tank, its internal and if it fails, so will the pump and it's not serviceable.
3) The VFD is covered in plastic. Most VFDs are. This is a horrible design since plastic does NOT dissipate heat well.
4) The VFD board is not coated, if moisture builds up in the pump (easy due to plastic construction) the board will short.
5) The motor itself is very cheaply made, not a NEMA frame, not commercial quality, light bearings and light on iron.

Finally, a well designed VFD as described in my article soon to be published in Pump and Systems magazine should last 15-25 years. Some will say that is impossible. I can understand their apprehension. But then again, the VFDs they are accustomed to and I make a living repairing, are designed to fail. They have a 40 deg C operating temp. They are plastic, they have membrane keypads that will fail.

A well built VFD is IP66 (wash down duty, air tight so no outside air mixes with inside air) and is rated for 60 degrees C. The motor AND drive should be powder coated Aluminum as not to corrode and be TEFC with a minimum of an IP56 design. Even the color makes a difference, black dissipates the internal heat best.

Poorly designed VFDs & pumps pay my bills so I don't complain.

BTW, there is a reason pump companies do not build commercial pumps for the residential market. With quality, comes cost.
I could not survive on building pumps for residential. 9 out of 10 people that inquire about pricing simply are not willing to pay the money for a product that will last.

In the long run, they pay more, much more and that does not include the aggravation and time it takes to keep replacing cheaper pumps.

Lastly, there is a reason the Federal government has mandated the use of VFDs in commercial pumps over 10HP. All pressure reducing valves cause excessive energy loss. It is like driving your car and maintaining your speed with the brake as the gas pedal is kept to the floor. So if energy savings is not a big deal, go that route but over a period of 10-15 years, the energy you wasted would have paid for a commercial grade VFD controlled pump, depending on size.

All the best,
Phil Tuttobene

Hi Phil
Boy did you hit the nail on the head with most of that stuff. I can think of a few more, but you listed most of the problems associated with Variable Frequency Drives, or VFD controlled pumps. Whether there are no well built VFD's for domestic use because no one will pay the price required, or just because the manufacturers are taking out quality to build in planned obsolescence is a matter of opinion. Kind of like which came first the chicken or the egg. The fact is there are no well built VFD's made for the residential market.

The few well built VFD's made for the commercial market are priced accordingly. Which would be fine if they actually did save energy. Most of the VFD's I have seen that lasted any length of time used an air conditioner to keep them from overheating. And in many southern installations the air conditioner for the VFD uses more energy than the pump and VFD combined. Not a good way to save energy.

Then if you look at systems like the ones in the pump and well and fresh water supply business, there is always a static pressure to maintain. When maintaining a static or constant pressure, a VFD will always increase the energy used as the pump is slowed down. The drop in horsepower and flow rate is not linear. Reducing the RPM of a pump will cause the horse power to drop by 50% alright, but the resulting flow rate will decrease by 90%. This means a VFD can increase the cost per gallon of water pumped by 300% to 500%.

When the water in the well is always 100' deep and the house always needs 50 PSI (115' of head), the pump must always produce 215' of head, regardless of the flow rate being used. Look at your pump curve. According to the Affinity Law when maintaining a constant head or pressure the pump can only be slowed by 10%-20% at most. With the drop in horsepower being many times less than the drop in flow rate, the cost per gallon pumped goes up, not down. Only with positive displacement pumps and pumps for friction dominated systems like large chillers could there possibly be any energy savings from a VFD. And nearly all pumps in the well pump and fresh water supply business use centrifugal impellers and are not positive displacement.

Then like LLigetfa says your analogy of one foot on the brake and one on the gas does not work with centrifugal type pumps. When the output of a pump with a regular centrifugal impeller is restricted, the horse power is reduced almost exactly as much as if you reduced the RPM. If you are going to say a VFD reduces energy consumption, then you have to say restricting with a valve also saves energy, because the cost per gallon will be almost exactly the same between a VFD and a valve.

It is a fact that restricting the flow rate of a pump with a valve will reduce the horsepower almost exactly the same as slowing the RPM with a VFD. This is a completely counter intuitive property of the centrifugal impeller. I would venture to say that only 2%-5% of the engineers in this world understand this counter intuitive property. Engineers don't do well with counter intuitive things. Everyone, even most engineers have it in their heads that restricting a pump with a valve makes the pump work harder, which is the opposite of the truth. Some of them get very angry with me for saying "restricting a pump with a valve makes the pump work easier", but that is a fact.

Lastly, the engineers who work for the Federal Government are obviously not in that top 2% to 5% of engineers who really understand how pumps work. Mandating the use of a VFD on pumps of any size is ludicrous, as it will actually increase the energy consumption in any system maintaining a static head or constant pressure. When a review of the actual work needed to be accomplished is done, (ie; pump x amount of gallons at y pressure), a VFD will always increase the amount of energy used. The fact that a VFD reduces the energy needed to spin the pump and motor confuses people into thinking a VFD saves energy pumping water, and that is far from the truth.
 

Sergio Zito

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From the description of your problem the key here to understand, is that when inlet pressure rises the pump fails to get a stable speed.
Looking how a VFD controlled pump work you must know a low speed limit is established, typically 25hz.
If running at its lowest speed the sensor detects the setpoint is being surpassed, it symply shuts off the motor.
As there is flow, pressure will drop and pump will restart, over and over.
When you rise setpoint (outlet pressure) the pump will need more rpm to get the setpoint, running ok. Same when inlet pressure is lower.
The trouble occurs when minimum speed is too much for requiered setpoint /flow/pressure working point: pump will cycle.

Another key is that if you can sustain 5 taps at 70 psi with this pump, is because inlet pressure and flow are very good, so the pump just “boosts”.
Seems to be oversized for your needs.

Installing a PRV on the inlet will make the system loose efficiency. More energy will be requiered for pumping all the time.
 

TheBigYahi

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HOOS1990, I know this thread is years old, but did you ever solve your cycling problem? I had the dealer rep out who agreed mine wasn’t working properly but I’ve had a hard time with them getting back to me with a solution.
 

Valveman

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If you search this forum for Scala2 you will find many threads on this subject like this one.
https://terrylove.com/forums/index....-on-start-runs-erratically.74730/#post-585212

As I said from the beginning there will be many problems with these, just because of the design. They are made to be easy to install and replace, because you have to replace them often. The slow start along with a teaspoon size built in tank are the reason for the water hammer, and I am not sure there is anything that can be done about it. When you open a faucet the little tank drains quickly. Then the pressure drops to zero while the slow start pump is getting up to speed. The drop in pressure waiting on the pump to get up to speed, then the quick increase in pressure once the pump is up to speed, causes the water hammer. And that is just one of many problems you will have with those type pumps.

If you want to stop the water hammer you need a regular/normal pump that gets up to speed before the pressure drops to zero. If you want something that will last 20-30 years instead of months, a regular jet pump with a Cycle Stop Valve and small tank will do that.

PK1A with Jet Pump vertical sized.jpg
 

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You only need to add a little Pressure tank at the outlets like the Flexcon FT8 and all your problems with the Scala2 will be solved. The integrated pressure tank is too small and the Scala2 begin to adjust their speed after 3-5 seconds.

I had multiples pumps design in search of efficiency for my geothermal setup, including big pump with CSV, 2 smaller pumps with CSV and 2 VFD Grundfos pumps and nothing run better than my current setup which is 1 Grundfos SQE with modded transducer for low pressure (5psi) and a Grundfos Scala2 to boost the pressure to 50psi in house. I had to add the pressure tank to the Scala2 to prevent cycling.

By adding a pressure tank, it help stabilize the pressure increase from the water heater too.

The Scala2 always restart and their last speed before going off.

I run this setup for 1.5 years now. It’s at least 3 time more efficient than my previous setup with 2 CSV. Now I use less than 500 Watts in the worst case. I have the most efficient pump setup the Canadian GeoExchange Coalition had evaluated at that time.
 

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1.5 years is good, but let us know in 10 years how many of those pumps you had to replace. Efficiency is good if you don't have to spend that extra money or more continually replacing pumps. You can make it even more efficient if you size the pump to exactly match the Geo demand and not have to vary the speed.
 

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I would also recommend to add a wx-101 or 102 tank down stream from pump if the pressure increase will be as low as 10 psi at times, with an incoming pressure of 60 the pump is over producing and building faster at 35 hz than your kitchen faucet can flow. I'm pretty sure Scala 2 max input pressure is only supposed to be 35 psi to work properly. Don't quote me I'm not looking at their technical data.
 

Valveman

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You only need to add a little Pressure tank at the outlets like the Flexcon FT8 and all your problems with the Scala2 will be solved. The integrated pressure tank is too small and the Scala2 begin to adjust their speed after 3-5 seconds.

I had multiples pumps design in search of efficiency for my geothermal setup, including big pump with CSV, 2 smaller pumps with CSV and 2 VFD Grundfos pumps and nothing run better than my current setup which is 1 Grundfos SQE with modded transducer for low pressure (5psi) and a Grundfos Scala2 to boost the pressure to 50psi in house. I had to add the pressure tank to the Scala2 to prevent cycling.

By adding a pressure tank, it help stabilize the pressure increase from the water heater too.

The Scala2 always restart and their last speed before going off.

I run this setup for 1.5 years now. It’s at least 3 time more efficient than my previous setup with 2 CSV. Now I use less than 500 Watts in the worst case. I have the most efficient pump setup the Canadian GeoExchange Coalition had evaluated at that time.
Which SQE pump do you have and how deep is it to water. Also what pump was working with the CSV. I'd like to do the math. If your not using the same pump we are not comparing apples to apples.
 

shane21

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As Flimboyz stated above in post#12 the main issue, and almost always the only issue, with rapid cycling from a SCALA2 pump is improper diaphragm tank pressure and/or volume. I agree that the built in pressure tank is too small for every application, and I also would recommend adding a very small additional pressure tank to the the system if you have rapid cycling issues, but much of the time just adding the proper amount of air to the built in diaphragm tank will solve issue. I like the Grundfos SQE VFD residential systems and have installed well over 100 of them, not so much a fan of the older MQ and newer SCALA2 booster pump systems. I will say that ALL Grundfos VFD systems are finicky with pressure tank size and pressure settings, more so than any of the other VFD systems I have ever installed or worked on, and have even had a representative from Grundfos engineering tell me even they are baffled from time to time by some of the finicky behavior of their pumps when the pressure tank size/settings are outside of proper values.

Back on topic, the bigger issue we have had with SCALA2 pumps is leaks. This includes one application where the original pump leaked within 1 year and the replacement pump leaked within 9 months of installation. This was a pump we installed in a property we owned and after having this issue in one of our own buildings we talked to our wholesaler and learned that leaking SCALA2 pumps were "not uncommon." Upon learning this we decided the SCALA2 pump was not a product we would be selling to clients until we could establish the leak issue was resolved.
 

HOOS1990

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As an update to this old post...I got the pump to stop short cycling. The problem seemed to be related to the incoming pressure (city water) fluctuations. Most of the time time the incoming pressure would be 35 - 40, and everything was fine. At others, the city water would be at 50 for several hours or more...and that is when problems seemed to happen. The simple answer was to put a PRV before the scala pump to keep incoming pressure at 40. I also adjusted the pressure of the tank appropriately.

However after getting that to work, I then noticed that when I turned on a faucet there would be a rush of water coming out at what seemed to be very high pressure. Suspicious, I put a pressure gauge on a faucet and watched with alarm as the pressure rose. The sequence was: 1) open faucet, grundfos runs and keeps pressure at 70 (set point) 2) close faucet 3) watch pressure gauge. With all faucets closed, the pressure steadily rose from 70 to 80, 90, 100, then 120! The process probably took an hour or so to reach 120. I tried a few adjustments, nothing stopped it, so I took the scala2 out of the loop and its been sitting, unused, for about a year. No more pressure spikes, so its definitely the culprit.

If anyone can offer advice on what is causing the pressure to spike, I'd be grateful. Otherwise, will need to do something, soon. We originally got teh pump in advance of an outdoor automatic sprinkler install...we are finally getting back to that project, and teh sprinkler guy says I need more pressure than 35 (that's in the basement where the water comes in the house, at "yard level" its actually a little lower)
 

shane21

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So the pressure rose from 70 to 120 over an hour? Was the SCALA2 running that entire hour even with the faucet closed?
 

Valveman

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LOL! All these problems from trying to vary the pump speed are the same problems I was having with VFD's thirty years ago. Even installing a hundred SQE's is not enough to really understand the problem. Installing a thousand SQE's and trying to keep them running for 10-15 years can cause someone to go out of business, or at least pull their hair out. There is an easy answer to all these problems. You can use a Cycle Stop Valve to maintain constant pressure and vary the flow with a simple pressure switch to make sure the pump comes on and off at the correct pressures. We have been replacing VFD systems this way since 1993. They keep saying the next generation of VFD's is going to solve all those problems, but mother nature will not let them change the laws of physics. Grundfos, Goulds, and most of the other pump companies knew the CSV was the answer back in 1994. However, they called it a disruptive product because it would make pumps last longer and use smaller pressure tanks. People who sell pumps and tanks do not like the CSV for this reason. But people who have had their lives disrupted and made expensive by a VFD will love the CSV.

Get a regular dumb jet pump with a dumb 40/60 pressure switch, use a simple CSV to make the system smart, and you will be able to live your life the way you want without having to worry about water coming out of a faucet when you open one.
PK1A with Jet Pump vertical sized.jpg
 

shane21

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Cary,

I have been in the business for over 25 years, like the CSV, have installed 50+ CSV systems and they have issues of their own, especially in systems with high iron and manganese content - though mineral content is likely not an issue with the OP's situation considering he is on a municipal water supply. I know all about the affinity laws, I understand fully that CSV's don't cause the pump and motor to work harder, and I can still say that no one system is perfect for every scenario - even a CSV. As for the total energy use, I was the first person at the first VFD seminars we attended to ask the manufacturers of these VFD's to provide us dealers some written literature showing the real world cost savings a VFD could provide, to help us sell the product, and never once did a manufacturer do that. Once I realized the manufacturers wouldn't put the alleged "cost savings" in writing I made sure our company never used cost savings as a sales pitch - understanding of the affinity laws makes it nearly impossible to believe a VFD will save you money over a CSV installation, but for a typical residential family of four I don't believe the energy costs of the two systems vary enough to matter for most homeowners.

Installing 100's of VFD systems over the past 15 years or so I can say for certain they are now pretty reliable as long as you understand how to install them and set them up. They have not caused us to go out of business or pull my hair out and, if anything, the demand for them in the industry is growing because so many people who have them like them and then tell others about them. That's not to say a CSV system won't do almost the same thing as a VFD (CSV systems don't provide soft starts for motors which is very beneficial for commercial and industrial submersible pump applications and the high total head caused by CSV's just sometimes isn't acceptable due to existing underground piping), but in some applications a VFD makes sense. Also you can't disregard the appetite some people have for technology and they like the simple intuitive display the VFD systems offer. I'm not saying that would matter to you or I, but it does matter to some.

In the case of the OP and the SCALA2, the main attraction may have been the advertised all-in-one nature of the SCALA2 product. While installing a CSV on a standard shallow well jet pump may seem easy to you or I, in reality it's not something everyone would describe as simple. Knowing how/where to install the CSV in relation to the pump and tank, moving the pressure switch (and the wiring involved in properly doing so), and then adjusting the pressure switch would be daunting to many homeowners whereas installing a SCALA2 is simple.

I do believe the SCALA2 will work for the OP, its just a matter of figuring out what problems he's having and helping him through the process.
 
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