Black + Decker Filtration (20x40)
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A 20x40' swimming pool is the largest of the standard sized swimming pools, typically having a total volume somewhere between 30,000 to 35,000 gallons and this could be more if the pool has a deep end greater than nine feet deep. Pools this large require a lot of filtration since there is such a large volume of water to handle. By comparison another very common pool size is a 16x32' and they might only have 15,000 gallons of water so the 20x40' pool is actually more than double the volume. Interestingly both size of pools mentioned would be installed with 2" plumbing lines (most commonly) and you might be wondering why a pool with double the volume is able to use the same plumbing sizes (and number of pipes) as a pool half the size.
The answer is that most pools are not built with efficiency in mind. This is why you will find something like 2" suction lines in everything from small pools up to gigantic pools, though in reality larger pools really should have larger plumbing lines. If I built a 20x40' pool tomorrow in my backyard it would have 3" if not 4" suction lines. So having 2" suction lines leaves a little to be desired. Still, this is the industry standard right now and if you are here reading this because you have a 20x40' pool then chances are that you have 2" suction lines also. Hopefully you have at least a few of them, though there are plenty out there with only one suction line. In fact, there are may 20x40' (usually older) pools out there still running with a single 1.5" suction line. It is far from ideal and certainly not efficient, but they do exist. If this describes your situation you might want to view this same variable speed pump schedule except using 1.5" pipes instead: Black + Decker filtration schedule (1.5" pipe size).
Filtration goals - Three turnovers of the pool volume daily will result in approximately 95% of the water in the pool being filtered at least one time. The first turnover nets 63% and the second nets 86%. The third 95% and a fourth turnover will result in approximately 98% of the water being filtered at least one time. A 20x40' pool with a 3.5' shallow end and 10' deep end might have an approximate volume of almost 40,000 gallons depending on the wall, floor and slope profiles. This means your ideal 24 hour filtration goal should be in the 120,000 gallons range. Yes you can filter less. Many residential pool owners do, but if you can have the best of both worlds in more filtered water but for less cost then perhaps it is worth considering. In the case of a large swimming pool with 2" pipe size like this example we will operate the pump near to maximum speed for the duration of the 24 hour day. Notably we run at less than maximum RPM since even a small reduction in RPM, and subsequent linear reduction in flow, will experience a dramatic and non-linear drop in the amount of power consumption that the pump needs.
24 Hour filtration example
Pipe size = 2" PVC
TDH = 30'
Filter pressure = 10 PSI @ 3450 RPM
Pump = Black + Decker 1.5hp (BDXBTVAR150)
Filtration total = 116,040 gallons
Electrical use = 22.53 kWh
24 hour cost = $2.93
Dialing down on pump motor RPM by even a little will have a fairly dramatic effect on the power that the pump is consuming. This is why the filtration schedule for this pool is all near to maximum speed, but distinctly less than maximum for the majority of the day. This allows us to reach a high daily filtration total while still spending as little as possible to do so. The pump power consumption goes down sharply as you begin to reduce the speed below maximum however the actual flow rates do not drop sharply. Instead the flow rates drop in line with the motor RPM as a linear match. If you reduce pump motor speed by 10% then you will reduce the flow output by a similar number, however the pump power consumption goes down greatly for even small drops in RPM. This is an affinity law of pump energy conservation and the basis behind why variable speed pumps use so much less power than single speed pump motors.
24 Hour schedule
5am - 12pm = 2500 RPM
12pm - 6pm = 3200 RPM
6pm - 1am = 2500 RPM
1am - 5am = 3450 RPM
After 24 hours we have a total of 14 hours at 2500 RPM, six hours at 3200 RPM and four hours at 3450 RPM. This provides a total of 116,040 gallons of filtered water for a total 24 hour cost of approximately $2.93. In this schedule example the period of time where we run the pump at maximum speed, 3450 RPM, is in the middle of the night. If you live in an area with variable electricity rates usually the middle of the night is when rates are the cheapest. Since the pump uses the most power at maximum speed you would experience the most significant savings by running the schedule with the highest power consumption during the time of day (or night) when electricity costs are the cheapest. This is just one example of a pool filtration schedule using a Black + Decker variable speed pump on a large pool system. There is in fact much more to consider as every pool system is unique and each pool has unique features, plumbing, equipment and layout. This is intended to help you research and better understand pool filtration systems, pipe size, variable speed pumps and how to apply these to your unique pool situation.
Filtration totals
2500 RPM (71 GPM) = 59,640 gallons after 14 hours
3200 RPM (90 GPM)= 32,400 gallons after 6 hours
3450 RPM (100 GPM) = 24,000 gallons after 4 hours
Total filtration = 116,040 gallons / day
Electrical consumption totals
2500 RPM (628 Watts) = 8.79kW after 14 hours
3200 RPM (1270 Watts) = 7.50kW after 6 hours
3450 RPM (1590 Watts) = 6.24kW after 4 hours
Total cost (22.53 x $0.13) = $2.93 / day
When pool owners shop for pool pumps they quite often will shop based on horsepower ratings on the pump, with the logic being that more is better. As you can see from this example we used only a 1.5hp pump while there are many 3hp pumps on the market. Even with only 1.5hp we achieved almost 120k gallons of filtered water per day. If you wanted to filter more, or filter better, the solution is not a larger pump but instead larger pipes. Even if you can not dig up and replace your plumbing lines you might be able to improve your system immensely with some new plumbing on the equipment pad. If you have multiple 2" suction lines on your pool that all meet together into a 2" suction manifold then you are sacrificing on potential flow improvements. Multiple 2" pipes should meet in a suction manifold at least one pipe size larger. In this case a 2.5" pipe manifold and 2.5" equipment pad installation would dramatically improve the flow and flow efficiency through the equipment. Most of the friction loss in your pool system happens on the equipment pad so this would be a great location to use larger pipes and slow down the water velocity for a given volume. Slow moving water moves much more efficiently than fast moving water through a plumbing system. Larger pumps will move more water but only a small amount more for a much greater total electrical demand.
It is important to understand that this page and this pump schedule for the Black + Decker variable speed pump is just an example. There are many variables to consider and this information should be used to help you better understand your own unique situation. The power consumed, flow achieved and total filtration requirements of your pool will be unique to only you and definitely different than the value you see in this example. This is intended to help you understand the relationship between flow and power consumption better so that you can make better informed decisions about your own pool filtration situation.
Watch this same schedule except with 1.5" plumbing lines instead: Black + Decker pool filtration for large pools (1.5" pipes)
Watch this same schedule tested on a 1.5hp Hayward variable speed super pump: Hayward Super Pump VS - large pool filtration schedule (1.5" pipes)
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