Why has the pool world been taken over by VFD's?

[armystud0911]

This post is partly a rant and partly me wanting honest answers from knowledgeable people here. I am ranting because I hate it when companies achieve a better product through better marketing, I hate this market speak and the mountains of BS that is hauled on the consumer as it trickles down the chain until they start raving to their friends about how great it is. People here "VFD" and think "Wow, that MUST be an awesome setup! It has a VFD! Those are so much more efficient!

I will be the first to admit here that I am fairly ignorant of pools, most of the people here know a lot more about them since they own and maintain their own. However, I do know a great deal about VFD motors and hydronic systems, and there is a great deal of marketing hype about these motors that makes me cringe when I hear it. I am trying to understand why a pool is a suitable application for a VFD.

First of all, people need to understand what, exactly, efficiency is, it is doing more work with less energy. A VFD is not efficient compared to a single speed pump, single speed pumps typically are a notch or two above a VFD when it comes to moving water with less electricity. All that a VFD does is let you slow the motor down so it uses less power and moves a LOT less water. A VFD also moves far less water for a given amount of electricity when it is slow compared to when it is running all out and especially compared to a single speed pump.

So if a VFD doesn't actually move your water with less electricity than why is it more efficient? I can shut off a normal pump and that is infinitely more "efficient" (to borrow the nonsensical marketspeak) than a VFD. I have maintained a friends pool for 4 years and we only run the pump 6 hours a day on a simple outdoor timer, what is so special about moving a little bit of water at all times? Most of the water won't actually run through the pump during these times of low use so you can't say it is being filtered. A little bit is being filtered all day so you really aren't filtering most of the water anyway and if you needed to, you could just turn a single speed pump all the way on.

So why would you want your pool's filtration system running at far lower capacity than it can run with but less electricity. From what I understand, (please correct me if I am wrong, I really do welcome it) most filters don't actually filter the water as well unless it hits a certain flow rate and pressure which it likely needs a pump running full speed to do optimally.

So what does running a filter all day do? You already have chlorine in the water, it is killing off anything that thinks of starting an ecosystem in your pool, sure the filter does trap particulate but I haven't seen a difference in water clarity between running a pump 24/7 and running it 6 hours a day, (as long as it is appropriately sized) so why do you need water pumping 24/7 even if it is just a little. Maybe some of the brighter people are remembering what they have learned about hydronics and that water flow is more efficient at lower velocities in your piping than at higher ones. Piping is cheap, why not just design your pool with larger pipes so the water moves with less friction and improves ANY systems efficiency? Maybe you WANT your water moving at a high velocity for some other reasons relating to how well it filters when there is more velocity. Well, if that is case, than why is running it at a low velocity with a VFD "efficient"?

Ok, so maybe some people here have a saltwater system and they need a water moving all the time because their fc levels will drop if there isn't flow. I thought you needed a decent amount of water flowing through your system anyway in order for these units to kick on in the first place, also, why not size them up a tiny bit so you can run the system for less time? Because it costs more? Not compared to a VFD upgrade!

 

[woodyp]

Ummmm..........nobody ever said there was a need to run a pump/filter 24/7 just because it's on low speed and lower speeds tend to filter water better? Half the flow rate at a quarter of the price vs. full speed satisfies a lot of needs.

 

[Griswald]

Also, the typical pool pump motor is not a VFD, it is a VS. VFD's alter the frequency of the electricity to speed up or slow down a motor with an infinite adjustment (well, almost infinite), VS motors simply have 2 or more sets of windings that can be switched to change the speed in steps.

VFD's are very expensive and require precise control systems, far beyond a normal pool pump application.

That said, I did try to scheme one from where I work to "test" it for my company! No dice...

 

[RobbieH]

I can't see why a filter would need a certain pressure before it operates. This might not be true for DE (I don't know much about DE filters) but a sand or cartridge is going to operate the same no matter the flow across the media.

And why operate 24/7? As stated above, twice the run time but using 1/4 the electricity during the run, the math is there. And some of us with very large pools and salt systems need to run enough to keep FC within range.

 

[dfahrion]

VS motors simply have 2 or more sets of windings that can be switched to change the speed in steps.

Modern electronics are making it economical to use either brushless DC motors or even 3 phase AC motors for VS pumps, and those can be more efficient than a standard single phase AC motor even given the same workload and speed. So most of the time you see a newer VS pump, they are actually referring to a brushless DC motor and electronic controller for it. The extra efficiency is relatively small though compared to the squared law efficiency of just running the pump slower so the gain of a fancy new DC pump vs. the classic 2speed is relatively small when compared to the huge gain of a 2speed on low vs. full speed. And it would not be hard to cost cut the efficiency gain out of the electronics so I don't think a claim that all DC based VS pumps are more efficient would even be safe to make.

 

[dschlic1]

As dfahrion has alluded to motor efficiencies vary greatly. For example my pump came with a single speed standard efficiency motor. I later replaced just the motor with a two speed high efficiency unit. Even at high speed there is a dramatic decrease in power consumption. So manufacturers came claim large efficiency gains for their new brushless DC motors over standard efficiency single speed motors. However when compared to a new high efficiency two speed motor the gains are not so evident. There are some gains to be had with running a pump slower in that head losses due to friction are lower. However the actual efficiency of the impellor is usually very low at low speeds. So there is a trade off.

 

[armystud0911]

Ummmm..........nobody ever said there was a need to run a pump/filter 24/7 just because it's on low speed and lower speeds tend to filter water better? Half the flow rate at a quarter of the price vs. full speed satisfies a lot of needs.

I agree there is no need to run any pump 24/7 but why does every marketing piece seem to rely on camparing to a single speed pump that is on 24/7?

 

[scooperhsd]

When my Hayward SuperPump (1.5 HP) died a couple years ago - I replaced it with a Pentair SuperFlo Hi Effiecincy (single speed 1.5 HP) pump. I can see that the Pentair is using less watts directly as the amps pulled are less (the Pentair is usually drawing about 5.5, the Hayward around 7 - both at 240 V). In retrospect - I probably could have used a 1HP or maybe even a .75 HP Superflo - and a 2 speed would be even better. I have used a Hayward PowerFloII .75 HP while I was inbetween pumps - I thought it did a decent job and I've been tempted to put it in place of the Superflo just to see if it can hold for the season.

 

[woodyp]

Key word------------"Marketing".

 

[FirstPoolLastPool]

I will add one comment on extended run times. If you have a lot of trees near and, in fact some over, the pool you can get a lot of pollen and other items steadily landing on the surface. Running the pump all day helps keep up with this problem and makes the pool attractive for swimming. Please note I am not talking about big leaves here or the annual fall event many of us contend with. I am talking about the March to September steady falling of pollen, seeds, acorns, husks, berries, etc. that some of us have to contend with.

In my case with lots of trees, relatively cheap electricity, new equipment with reasonable efficiency and my new best friend SKIMMER SOCKS, long run times yield maximum enjoyment at reasonable cost. Also, we like the sound of the waterfall during the day to mask other noise and bring some limited amount of zen and peace since we have two people working from home every day.

Just sayin...

 

[Isaac-1]

Another advantage of VS pumps is that a single pump can replace 2 or possibly 3 fixed speed pumps, think of pools that would traditionally have not only circulation pumps, but also water features, spa's, etc.

Ike

p.s. as to your comment about using larger plumbing this is fine on new construction, but options for this are limited when the plumbing has been under concrete for 30+ years and was installed in an era when people were far less concerned about electric rates.

 

[Shirker]

Yes to Skimmer Socks! I can't believe the amount of junk I am preventing from going into my filter. Mostly insect parts (fire ants), fine debris from cutting grass, and little almost microscopic bits of styrofoam from the kids's noodles.

 

[CUTiger78]

I guess I'm missing something - the pool world has been taken over by volunteer fire departments???

 

[chem geek]

So if a VFD doesn't actually move your water with less electricity than why is it more efficient? I can shut off a normal pump and that is infinitely more "efficient" (to borrow the nonsensical marketspeak) than a VFD. I have maintained a friends pool for 4 years and we only run the pump 6 hours a day on a simple outdoor timer, what is so special about moving a little bit of water at all times? Most of the water won't actually run through the pump during these times of low use so you can't say it is being filtered. A little bit is being filtered all day so you really aren't filtering most of the water anyway and if you needed to, you could just turn a single speed pump all the way on.

So why would you want your pool's filtration system running at far lower capacity than it can run with but less electricity. From what I understand, (please correct me if I am wrong, I really do welcome it) most filters don't actually filter the water as well unless it hits a certain flow rate and pressure which it likely needs a pump running full speed to do optimally.

See this post I wrote showing that even accounting for run-time so you get the same number of turnovers, lower flow rates use less total energy (the numbers shown are with my solar system turned off). The reason is that the energy usage rate (Watts) does not vary linearly with flow rate (GPM) and varies closer to the square (in my case, to the power of 1.8). So your assumption that the total energy used per turnover is the same regardless of flow rate or pump speed is wrong. Of course, a 2-speed pump also allows for a lower speed, but it is very clear that one can get very large energy savings using either a 2-speed pump or a VFD pump compared to a single speed pump.

You are also incorrect in your assumption that filters do not filter well except above a minimum flow rate. In fact, the opposite is true if one uses a pump oversized for their filter then the excessively high flow rate can push material through the filter that would have otherwise been caught and such high flow rates that exceed filter specifications can damage the filter (especially cartridge). So, no, there is nothing wrong with using slow flow rates through filters.

One should not underestimate the importance of being able to tune more precisely the flow rate to maximize efficiency. In my own pool I went from using a Jandy HHP 1 HP full-rated (1.65 Service Factor) single-speed pump at around 1800 Watts plus a 3/4 HP booster pump for the pool sweep at around 1400 Watts and replaced these with a Pentair Intelliflo VF pump.

If I tried to keep the same flow rate that I had before when the solar panels were on of 55 GPM, it would be over 2000 Watts so less efficient than my older pump. The variable speed pumps are often not as efficient at high speed though that may largely be due to different wet end designs since they want to be very efficient at slower speeds that are more commonly used most of the time. However, I lowered the flow rate to 48 GPM which was optimal for the solar panels (4 GPM per panel) and this lowered energy usage to 1500 Watts, a savings of 300 Watts and if I wanted to I could go even lower in flow for more savings though slightly sacrificing some solar panel heating efficiency. If one accounts for the longer pump run-time needed, the savings mostly goes away (since the GPM change wasn't large -- with larger GPM changes lower speed is noticeably more efficient even adjusting for run time) but with solar it's on as needed for the same amount of time with either pump type and the efficiency difference of the solar heating at these two speeds is negligible so the energy savings in pump electricity is real.

When the solar was off, I go down to 26 GPM and only use 275 Watts, a savings of 1525 Watts. I also eliminated the booster pump and run the pool sweep directly (I switched from a Letro Legend to The Pool Cleaner) at 15 GPM for 540 Watts, a savings of 860 Watts. Also, when I run the gas heater during the extended season, I run it at 40 GPM for 615 Watts, a savings of 1185 Watts. A 2-speed pump on low speed might not be able to meet the minimum 30 GPM flow rate of the heater and really one should not run that close to the edge for a heater since it wears out faster at such higher internal temperatures.

The net result is that I cut my pump electricity cost from around $1500 per year to $700 per year (it's more now due to even higher electricity rates, but this comparison is at the equal rates of 35 cents per KWh). A 2-speed pump is not as efficient as the VF pump at low speed, but it is very true that it doesn't make sense to replace a single speed standard pump with a VFD if one is going to only use the same high flow rate. If I had a 2-speed pump with 3450 RPM at high speed and 1725 RPM at low speed, the low speed would not be as efficient as the VF pump and I'd still need to do something for a pressure-side cleaner. Even so, it is true that a large part of my savings could be achieved with a 2-speed pump, though with the VS/VF pumps it's not just VFD, but also the use of permanent magnet motors instead of induction motors that lead to some of the additional efficiency. The pump is also very quiet and should last longer (mine is 6 years old).

 

[rmturner54]

I use the saying of slower the better. Meaning the slowest possible speed to achieve the end results needed.
A fixed multi speed pump will most likely never be manufactured for the speed that's most efficient for a particular situation.
That's why a VS...variable speed is best.
A vfd is not a a motor but a drive. The majority of places vfds are used is in 3 phase applications. Very few found for smaller
Hp apps.

 

[SwimmingpoolAZ]

It may have already been said but pools are like snow flakes, each one is unique in it's needs and with the VS pumps you can tailor your pump to do only what is needed with no overage. Got a suction cleaner? no need to run it 8 hours a day, you wouldn't vacuum your living room that long. Extend the intervals between servicing your vac and only run it 3ish hours a day. run the rest at low speed, take all day to turn the water over instead o letting the water sit stagnant for 10-16 hours at a time. You're not only going to save on electricity but also on maintenance time and chemical costs. Take it from someone who has been installing them on pools he takes care of. My customers are happier with their electric bills and chemical costs and I'm happy showing up to a pool that requires less work. To me it's a no brainer.