Variable Speed Pump Objections
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There has never been more talk about variable speed pumps than there is right now as 2021 is the year where pool owners are being forced to switch from single speed pumps to more efficient filtration pumps. The next time that your main filtration pump needs repair or replacement you will find that your replacement options are more limited than they used to be. This is an effort to reduce on wasted energy, something the swimming pool industry is unfortunately doing in wholesale quantities...or more accurately was doing. Now pool owners will be responsible for upgrading their equipment to more energy efficiency models, of which variable speed pumps are the primary option. There are some smaller single speed pumps available still, under one horsepower, but the vast majority of filtration pump options will now be variable speed.
When faced with a much more expensive pump option you might be inclined to wonder if you are getting taken advantage of. Is this just another cash grab by some industry railroading you into buying something you don't want? I definitely do not think so, and for what it is worth I personally would be just the kind of person to take issue with being forced to buy something I "didn't know I needed" until I walked through the front door of your store. In this particular case it just so happens that I know a lot about pool pump motors, electricity, plumbing and system efficiency. Knowing all of this makes it a LOT easier to accept spending more on a new variable speed pump because I know that this is simply superior technology and it will return on your investment greater than the entire purchase price of the pump when used correctly. So while I agree that it is frustrating to be told you need to spend more money upfront for your pump you will benefit from this in the long run.
In this article I want to look more closely at some of the reasons that people list as negatives for variable speed pumps. There are a host of counter arguments used against buying variable speed pumps however not all of these are as valid as the rest. Let's take a closer look at some of the reasons why people might say you should avoid a new variable speed pump for your pool:
I only run my pump 8 hours per day
This is the first argument you will hear against variable speed pumps from people who do not understand fully the nature of energy consumption for centrifugal pumps. While there is definitely merit to the logic that a pump running eight hours per day will certainly use less power than the same pump running 24 hours per day, that is where the validity of the argument ends. With single speed pumps when you want to save money on electricity you must turn them off. With variable speed pumps when you want to save money you need to let them run around the clock. The pump affinity laws show that when you reduce the pump motor RPM by half the pump power consumption drops to 1/8th the full speed value. That is a huge and important takeaway. Flow is linear and follows motor RPM, so dropping the motor RPM in half will result in approximately half of the flow of the full speed operation, but only 1/8th the power consumption.
Having the ability to control motor RPM allows you to harness the pump affinity laws for energy conservation benefit. So in an apples to apples comparison between a single speed pump running eight hours per day and a variable speed pump running 24 hours per day the variable speed pump will cost (a lot) less to operate, and will actually move more water every day than even a reduced operating schedule for a single speed pump. Home owners would absolutely never accept the level of inefficiency from a single speed pump from any other appliance in their home. If you had even a medium sized single speed pump that you ran 24 hours per day, as some pool owners do, this would account for up to 50% of the total monthly electricity use for the average home. Single speed pumps are absurdly inefficient and it is about time we improved this technology. They cost less to run, run quieter, run cooler, are more dynamic for flow control and they eliminate any periods of stagnant water in your pool.
I need high flow rates for my heater/salt system
One of the first objections that you might hear about a variable speed pump relates to the reduced flow rates that you will have and how this would be a problem if you have a pool heater or something like a salt water chlorinator that takes many hours of operation each day in order to function properly. While these are valid comments to make in that pools do need adequate flow for the peripheral items and devices installed, this is an unfounded fear when you actually start to look at the data provided by the equipment manufacturers. Salt chlorinators for example require fairly low flow rates for the flow switch to close and the unit to start producing chlorine. The flow rates that chlorinators need to work properly is actually low enough that most systems will achieve this minimum flow level with only a few hundred RPM on the pump. Using a salt chlorine generator is clearly no excuse to avoid variable speed pumps, in fact salt systems and variable speed pumps work amazingly well together. Here is an article that looks further at pump speed for salt chlorinators. While heaters do require more flow than salt chlorinators as you will see heaters also are able to operate at low RPM range for most pools making them ideal for use with variable speed pumps.
Pool heaters require a little more flow than salt chlorine generators in order to operate safely, so this is a more legitimate concern for compatibility with variable speed pumps than salt chlorinators. However what we see when we look at the data provided by heater manufacturers is that the minimum flow rates needed for most heaters is also quite low. Perhaps not quite as low as with salt chlorine generators, but still appreciably low such that any pool system should be easily able to meet these flow requirements on less than full speed operation. Most systems should be able to meet this flow value with less than half speed operation even, but every pool system is unique. It should also be noted that meeting the minimum flow rate to close the pressure switch is not the ideal flow rate for heating your water. You should attempt to move your water faster than the minimum values for your heater as this is better for waffling on/off with barely adequate flow, as well as being bad for the heater if your flow rates are chronically too low. Fortunately there is a lot of room in between full pump motor speed and the minimum speed needed to close the pressure switch on most heaters. This means that you will still be able to benefit from reduced operating costs for your pump motor when your heater is running, and this is due to the dynamic nature of variable speed pumps and their ability to control and set flow rates.
Low flow rates are bad for your pool circulation
An argument against variable speed pumps that you hear people say quite often is that you can not turn down the flow of your pump because that would be bad for the pool. I find this to be a funny argument in that it advises against lower flow rates as this is bad for the pool. How then can it be good for the pool to have 12 or 16 hours every day with the filtration system fully off and the pool water sitting completely stagnant. That sure does not sound like how you achieve the best possible filtration of your pool water. Slow and steady wins the race for pool filtration. Which should make a lot of sense when you really think about it. How could eight hours at full speed followed by 16 hours of dead stop possibly be better than a dynamic 24 hours flow schedule with periods of time at different speeds and flow rates for the various features and functions of the pool? The answer is that is simply is not. Single speed pumps are old technology that is overdue to be replaced with something much, much superior...variable speed technology.
Flow rates for filtration should not be a static number. A well designed and programmed variable speed pump schedule should have periods of time at high speed operation for maximum circulation of the pool and effectiveness of the pool skimmers. You should also have some hours of operation each day at medium speeds which still have impressive flow volumes but have much less power consumption than the high speed operation. Finally variable speed pumps should all include long hours of operation each day at low RPM's. This is because water moves very efficiently at low speeds as there is little in the way of friction or turbulence in the pipes. The faster the water moves the more inefficiency from friction and turbulence are introduced. Long hours at low RPM operation will result in the most efficient movement of water for filtration and least efficiency losses in your system. A few hours at high speeds, a few hours at medium speeds, and then the remainder of the day at low speed operation is the best way to program your 24 hour filtration schedule. This will give you the best quality of water filtration along with the lowest cost of operation for your equipment. Just be sure to get a flow meter as without one you can not tell how much water your system is moving, or whether you are moving any water at all! Low RPM operation is very quiet and hard to determine if you have flow at all...even when you have as much as 20 or 25 GPM! For more information you can read this article on pool flow meters.
Variable speed pumps are expensive to repair
You do not need to look very far to find (older) pool technicians talking about how expensive variable speed pumps are to fix or replace parts. For the most part this is true. You have a computer driven pump now and if that drive fails this will cost a lot of money. Just like one of the computers in your car that regulates the extremely high tech and dynamic operation of your car. If one of these computers fails it is going to cost a lot of money for the parts to fix it. Further since you are replacing a computer on your car you will need to pay someone with more experience than your local oil change shop. These are all parallels for variable speed pumps and yet look at all the modern commuter cars out there on the roads. Saying that variable speed pumps are high tech and can break and will cost a lot to fix would make sense if everyone drove carbureted cars from the 1970's but that would be silly. Those cars are super inefficient on fuel and new cars with advanced fuel injection and variable valve timing are so much more fuel efficient...uh oh. I think we found another parallel to variable speed pumps!
When an old-timer pool technician tells you that variable speed pumps are not good because they are expensive to repair and too fancy, ask to see their phone. I would be willing to bet this person is not in possession of a new generation apple or android device, but more likely operating with a half-smashed flip phone from the late 90's. Is this the person you want to get your technology advice from? Variable speed pumps are high tech when compared to single speed pumps with no amperage or motor RPM control but that is not necessarily a bad thing. There are very few other areas in your life where you are using technology unchanged from 1960's as most things get improved over time. It took a while but pool pumps have been improved and as such there will always be early adopters and later adopters. When you are being told that variable speed pumps break and can cost a lot to repair you are likely speaking to someone who adopts new technology slowly, or had a negative experience with variable speed early on. There were some early models with higher than average failure rates which might have helped to leave a bad taste in the mouth of some pool owners or pool technicians, but this is something that would be the exception, not the rule. By and large variable speed pumps are meeting and exceeding expected service life duration due to lower heat generated from lower RPM operation, closed motor design limiting dust and moisture failures and people being more particular with the installation. Being that these pumps are expensive people might pay more attention to the installation guidelines than normal. Quite often when pumps fail early it can be traced back to poor or incorrect installation or sizing of the pump. For more information you can read this article about replacing a pool pump.
From these videos we can see that variable speed pumps cost less to operate 24 hours per day than a single speed pump that you run only 8 hours per day, plus you move more water with the variable speed pump at the end of the day even though it consumed less electricity. The pool no longer sits stagnant 16 hours per day and you have a dynamic filtration schedule that includes times at low, medium and high speed operation for the different functions your pool needs and peripheral devices that you have like salt water and heaters. We also now know that water moves much more efficiently at low speeds than at higher speeds due to friction and turbulence introduced at higher speeds. Finally we know that just because something is fancy new technology with computer controlled function does not make this a bad thing. In fact we all enjoy fast cars with low emissions and great fuel economy versus cars of previous generations. Now pool pumps will be the same way. Once you actually see the math on how much you save and how well they work it is pretty hard to argue against variable speed pumps for pools.
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Swimming Pool Steve is an award winning, second generation swimming pool and spa specialist from Ontario Canada. With over 10,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the 2018 Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
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