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Thread: 'reactive' approach

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    'reactive' approach

    This post was split from a different thread here. TheBlizzles

    Running the pump to get clear water is a 'reactive' approach. There's plenty of research that show that commercial pools generally need a 6-hour turnover and a residential every 12 hours. The temptation with variable speed pumps is to get the maximum energy savings by slowing down as much as possible - heck, some of them even have a watt meter in the display. I watched a buddy (homeowner) of mine install a VS pump and then knock the speed down until he just had flow over a water feature and had the lowest wattage - no account of turnover. He found the results of his folly some days later when the pool started to go cloudy. Now he has to chase the problem and get the pool back in balance.
    To use another analogy, would you buy a car without a speedometer?

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    Mod Squad jblizzle's Avatar
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    Re: Has anyone hooked a flow meter to a pool with an Intelli

    Quote Originally Posted by phackett
    Running the pump to get clear water is a 'reactive' approach. There's plenty of research that show that commercial pools generally need a 6-hour turnover and a residential every 12 hours. The temptation with variable speed pumps is to get the maximum energy savings by slowing down as much as possible - heck, some of them even have a watt meter in the display. I watched a buddy (homeowner) of mine install a VS pump and then knock the speed down until he just had flow over a water feature and had the lowest wattage - no account of turnover. He found the results of his folly some days later when the pool started to go cloudy. Now he has to chase the problem and get the pool back in balance.
    To use another analogy, would you buy a car without a speedometer?
    This is not exactly what we have found and recommend. There are studies that show that for adequate chemical distribution, pools need VERY little pump ON time (1-2 hours). So, our recommendation is to run the pump long enough to keep the pool clean enough for your liking which is certainly enough for chemical distribution ... a little dirt or leaves do not cause a problem as long as the FC is maintained. If someone wants a crystal clear, nothing floating anywhere, pool then they will want to run the pump a lot longer that others who do not care if the water is crystal clear. Note I am not saying "cloudy", but I mean suspended dirt, etc. A cloudy pool could indicate the start of algae due to the chlorine not being maintained high enough.

    Sure the flow rate can affect the ability of the skimmer to properly work which can affect how much debris ends up floating around in the water. BUT, having that low flow rate will not result in a cloudy / algae filled pool if the FC is maintained properly.

    One has to balance the pump speed and run time to have the skimmer work and in the case of SWG, to generate enough FC; but there really is no need to ensure X number of turnovers in X number of hours.

    I think your flow meter is a really nice device for those that are looking to dial in their system ... maybe more for solar applications ... but I don't think the "adequate turn over" is an appropriate argument.
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    Re: 'reactive' approach

    Residential and commercial pools are extremely different situations. Commercial pools need to base their pump run time primarily on bather load, as filtering of debris introduced by bathers is the dominant consideration. In outdoor residential pools bather introduced debris is minimal and surface clearing becomes the dominant issue. A large study sponsored by an electric utility recently showed that reducing pump run time by a factor of 2 to 4 and spreading the remaining run time out over the full 24 hour period in many fairly short periods resulted in dramatic energy savings, while maintaining identical water quality and reducing the need for vacuuming. This approach optimized surface clearing, catching debris on the surface before it sinks, which turned out to be the dominant factor in a residential pool's need for pump run time.
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    Re: 'reactive' approach

    Thank you for your positive feedback on the flow meter.

    I wanted to mention that the manufacturers of the numerous variable speed pumps disagree with an approach of running the pump for just a few hours per day, indeed, they have been quite vocal on this topic at all of the seminars that I have attended, and say 'run it slower, run it longer'. With the significant energy reduction coming from running the pump at say even 60% speed (an almost 80% reduction in energy cost), wouldn't it make sense to let the filter have a more consistent / even flow rather than expecting it to do all of its work in just a couple of hours each day? Running at 60% speed for 24 hours equates to the full speed energy consumed in just 288 minutes!

    I guess I don't know how you determine what running at a slow flow rate is without an instrument to tell you what you are doing. One persons interpretation of running slow is different from another. You cannot simply say run at 60% speed because the head on every pool is different and therefore the flow will be different.

    Incidentally, the commercial 6-hour t/o originates from a perfect storm situation of maximum bather load on a hot summer day and kids defecating in the pool. In most States, there is no flexibility in this sledge hammer approach and the pumps are run 24:7 to achieve the mandated t/o. Some States are allowing a drop to 8 hours during unoccupied times.

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    Mod Squad Bama Rambler's Avatar
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    Re: 'reactive' approach

    You obviously have a dog in this hunt, and that's ok, but at least realize that it's pretty easy to determine how fast or slow the flow rate is just by looking at the movement of the water. You don't really need a specific number of gallons per minute in a residential pool. I agree that it's something nice to know but it's not absolutely required.

    I plan on buying one of your flow meters, but I'm a gadget guy and have way more gadgets than I actually need.

    As stated above, the determining factor in run time for my pool is keeping the surface skimmed. With the amount of leaves we get I'm always going to have to run the pump more than enough time to turn the water over in the pool. I'm most likely going to go to 6 shorter run intervals per day instead of the 3 I now run.
    Dave J. TFP Moderator
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    Re: 'reactive' approach

    Quote Originally Posted by phackett
    wouldn't it make sense to let the filter have a more consistent / even flow rather than expecting it to do all of its work in just a couple of hours each day?
    What kind of "sense"? You need to define what the criteria are or statements like that don't make any sense.

    The ideal pump speed, based on electrical efficiency (gallons moved per watt), for the current crop of variable speed pumps is around 900-1000 RPM. Some pools need to up that speed a little to get the skimmers to skim effectively, though that is fairly uncommon. Baring other optional factors (pool cleaners, water features, etc) that determines the ideal pump speed.

    The ideal pump run time and schedule should be based on things like maintaing water clarity, proper chemical mixing, elimination of dead zones, and such. Proper chemical mixing and elimination of dead zones turn out to be simple, and happen with exceedingly short pump run times. They are mostly determined by proper layout of returns and return aiming.

    Water clarity/quality in an outdoor residential pool is dominated by externally introduced debris, most of which floats for a time. It only takes a short amount of run time, generally less than half an hour, to clear the surface. Then you just need to make sure that happens often enough that the debris doesn't sink, which seems to be four to eight times per 24 hour period (depending on the debris types common in your area).

    There are other factors affecting water clarity/quality, but in a typical residential pool they are easily handled with quite short pump run times. There is still bather introduced debris to filter, but typical residential pool bather load is very light and that translates into very short pump run times. In most cases, again assuming light bather load, these factors are all handled within the run time determined by the surface clearing requirement.

    This approach won't work for every residential pool. Large families with lots of kids swimming all the time can require significantly more filtering and various optional accessories, like pool cleaners, solar panels, and water features introduce noticeably higher minimum flow rates when they are in use.

    Variable speed pump manufacturers base their recommendations on the assumption that you already know how many turnovers you need. Given a known turnover requirement, energy efficiency dictates a low motor speed for a long period of time. In a commercial pool situation turnover requirements are generally set by code and are well known. In a residential setting assuming that the turnover requirement is known is a bad assumption, invalidating the pump manufacturers recommendations. Residential pool owners have not the slightest idea how many turnovers they need, nor is the prevalent "common wisdom", the stories and rules of thumb typically passed down from person to person, accurate in a residential situation.
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    Re: 'reactive' approach

    Quote Originally Posted by phackett
    I guess I don't know how you determine what running at a slow flow rate is without an instrument to tell you what you are doing. One persons interpretation of running slow is different from another. You cannot simply say run at 60% speed because the head on every pool is different and therefore the flow will be different.
    I agree that RPM is not enough but this is true of flow rate as well. Just because you have the same flow rate on two different pools does not mean that they will behave the same or be equally clean. The skimming action could be different due to skimmer placement, prevailing winds and the amount of debris the enters the pool.

    The point is, that every pool is unique and so some experimentation will always be necessary to optimize both RPM and run time to minimize energy use. Because of this, I really don't see much value in knowing the exact flow rate. It doesn't tell the average PO anything they actually need to know.
    Mark
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    Re: 'reactive' approach

    It's too bad this thread was cut in two. The first post in this new thread didn't make much sense to me until I saw the original thread.

    The practice of pruning threads like this isn't helpful.
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