Do Pools Need Flow Meters?
Do swimming pools need flow meters? The vast majority of existing residential swimming pools, somewhere in the range of 95% of them, do not have a flow meter installed on the plumbing system. What this means is that there is absolutely no way to quantify how much water is traveling through the system at any given time. Is this an issue? It didn't use to be but this is definitely something that is going to become an issue moving forward, and new pools are going to need to start installing flow meters as part of the standard equipment packages. Flow meters were always a good idea, and many commercial swimming pools already benefit from flow meters as part of health and safety requirements relating to flow and filtration minimums.
Residential pools are not operated the same way, and with the same scrutiny, as commercial pools. There is liability in owning a residential pool, but obviously the potential for issues are vastly greater with a commercial swimming pool that is open to the public. What would happen if someone became sick and died potentially from poorly treated pool water? That kind of thing certainly can and does happen. The operator would need to be able to prove that the pool is cared for up to established commercial standards for turnover rate and chemical management. The only way to know, or prove anything, would be to know the exact flow rate of the plumbing system. In theory, for both liability but also just for proper care and maintenance, residential pools should be operated the same way as commercial pools. You should be able to know, at any given time, exactly how much water you are moving through your filtration system (and what your chemical levels are).
Filtering swimming pool water - Filtering pool water in a backyard pool tends to be an entirely less scientific process than it is intended to be. In order to filter your water every day you need to actually filter the entire volume of your pool four times over this period. This is because your dirty water does not line up single file to be filtered, and due to diffusion it will take four turnovers of the pool volume through the filter before you can know that you got over 98% of the water at least once. Again, residential pool owners tend to care little about this discussion and use the pool water itself as a visual guide. If the water is green filter it more, if the power bill is too high, filter it less. This haphazard approach to water maintenance is one of the main reasons that people have trouble maintaining their pool. The people that have an easy time of caring for their pool probably have a better and more thought out filtration schedule than others.
Why Do I Need A Flow Meter?
Even if your pool has never "needed" a flow meter before you will want to have one moving forward. It used to be, with single speed pumps, that pool owners would base their filtration schedule upon how many hours per day their pump would be running. While fairly unscientific this was good enough for at least most swimming pool owners to keep their water clean and clear. Pool owners often would have schedules of four hours daily, eight hours daily or 12 hours daily. Simply due to electricity costs there are not all that many pool owners who run their pump 24 hours per day, though there are some. For comparison purposes you might like to read these articles where the electrical savings and filtration volume of single speed pumps and variable speed pumps are compared based on these reduced filtration schedules:
Running your pump 4 hours per day
Running your pump 8 hours per day
As you see in these articles when you use a variable speed pump properly, which includes calculating and dialing in the exact flow rates that you need, you will save a substantial amount of money on electricity, even over and above these already lean filtration schedules. If you are one of the people who runs their pump 24 hours per day right now then you are going to see the most savings from upgrading to a variable speed pump and dialing in the flow schedule.
It used to be that if the pool water stayed clear then you were filtering enough. If it went green then you needed to filter it more. Now with variable speed pumps you should aim to run your pump 24 hours per day. Shutting off the pump no longer saves you money...it now costs you money. The most savings you will get from your VS pump will be from the long hours it runs a low RPM speeds. These long hours at low speeds are where you make back all of the money you invested, and then some, so turning off your pump at any time would be a mistake. Instead you want to have a few hours at higher speeds, a few hours at medium speeds, and the remainder of the day on very low RPM speeds.
The purpose of flow meters and variable speed pumps is to remove the guesswork out of pool filtration. Each system is unique and you will need to learn about the flow requirements for the peripheral items on your pool, like heaters or salt water systems, and so the "perfect" filtration schedule for a variable speed pump would literally change from pool to pool. However without a flow meter installed on your pool system you will not be able to start the process of calculating your filtration schedule since you will have no idea how much water your pump is moving at different RPM speeds. The first steps in making your pool more efficient is to know how much water you want to filter, and how much you are actually filtering.
How much of the total pool volume gets filtered per turnover:
1 turnover = 63%
2 turnovers = 86%
3 turnovers = 95%
4 turnovers = 98%
For my residential pool I aim for three turnovers every 24 hours even though the commercial standard is four turnovers. I am happy with 95% of my water being filtered every day and my water never turns green. Many pool owners are happy with less filtration than this, however most of them could not tell you just how much of their water is actually getting filtered. Probably most of the residential pools out there are operating at one to two turnovers daily, which puts them in the 63% to 86% range. Most likely the pool is not going to turn green with this level of filtration, assuming the water chemistry stays maintained, but an increase in bather load, rain water, fertilizers, sunshine or any other number of factors could change that and cause the pool to begin to go murky or turbid.
Important note for reducing chemical exposure - Modern day swimming pool owners are very sensitive to what they put in their pools, and in their bodies, and there is a strong push for reduced chemicals (or no chemicals) in pools. I appreciate the desire to avoid unnecessary chemical exposure, but I also understand better than most the extreme dangers of poorly treated water. The first step to reducing the amount of chemical exposure in your pool is to filter the water more. Every last iota of debris in your water needs to be removed by the filter or the chemicals. If you only do one turnover of your pool water daily, which means only 63% of your water actually got filtered, now your chemicals need to work to sanitize and oxidize the remaining 37% of the water that did not get filtered. All that organic debris uses up your chlorine, and then requires more chlorine and additional pH and alkalinity control chemicals. If you want less chemicals in your pool without compromising your health or safety, then simply start filtering your water more. This is easier (and cheaper) than ever with new variable speed pumps.
For more information you can read this article about how a variable speed pump will save you money. If you are ready to get a flow meter for your pool so that you can start to dial in your flow rates (and savings) then you can check out this article all about swimming pool flow meters
Swimming pool flow meters
Running a pool pump 4 hours per day
3 reasons to get a variable speed pool pump
How much electricity does a pool pump use
How does a variable speed pump save you money
Variable speed pump schedules
Variable speed pool pump reviews
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