Filtration Schedule For A 14x28' Pool
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Buying a variable speed pump for your pool is one of the single best cost saving upgrades you can make to your home. The difference between the cost to run a single speed pump and a variable speed pump is just about night and day different. You can see here in this example breakdown how this pool would experience $4300 in electrical savings just by switching to a variable speed pump. The best part is that the filtration of the pool is not compromised with this upgrade...it is enhanced. A dynamic filtration schedule with variable speeds at different times of day is undoubtedly superior to a static pool filtration system as you can customize a variable speed pump to meet your unique needs. With a single speed pump all you can do is turn it off for part of the day but even this is not as effective at improving electrical efficiency as you might hope.
Better and more filtration for less money is the claim with variable speed pumps and the proof is as easy as taking measurements for yourself. Even pools with already lean filtration schedules where the pump only runs for part of the day still fail to be able to save anywhere near to as much as a variable speed pump 24 hour schedule as evidenced in this comparison article where I look at a single speed pump running for eight hours daily and compared to a variable speed pump running 24 hours per day. In short, the variable speed pump costs about half as much to filter the exact same volume of water every day. 8 hours single speed VS 24 hours variable speed.
Example pool
Size: 14'x28'
Volume: 13,230 gallons
24 Hour filtration goal: 39,690 gallons
Pipe size: 2" suction and discharge
Pump size: 1.5HP Pentair Superflo VS (115 Volts)
System TDH: 25' head
Why is the 24 hour filtration goal so high? - Your goal as a pool owner should be to filter all of your pool water every day. This is the best way to keep your pool water clean and clear with the least possible amount of chemical intervention. Every speck of debris that you fail to remove via mechanical filtration now needs to be dealt with by the chemical sanitizer in your pool. By filtering all of your water every day you will keep your chemical use at the absolute minimum value. Unfortunately in order to filter all of your pool water you will need to filter much more than just the volume of your pool. The first pass of your pool volume through the filter will get about 63% of the water in your pool and a second turnover will bring this number up to around 86%. The third turnover of your pool will result in 95% of the water in your pool being filtered at least one time. For residential pools this is typically accepted to be "all" of the water in your pool. If you elected to pursue a fourth daily turnover this would net you an additional 3% for a total of 98% of all the water in your pool being filtered at least one time. Four is fine if you want the best possible water but for most residential pools three turnovers for 95% of the water should be considered sufficient.
Why do I need low, medium and high speed settings? - A well designed variable speed pump filtration schedule should include times of day where motor speeds are low, medium, and times where the flow rates are quite high. This dynamic arrangement allows for the best of all worlds in that the long hours at low speed provide massive filtration volume for pennies on the dollar, where mid speed and high speed operation increase the diffusion and circulation of the water in your pool which allows for effective skimmer functioning as well as the activation of peripheral items that require flow to operate like salt chlorine generators or heaters to operate. Every pool is different and perhaps yours does not meet this typical expectation of low, medium and high speeds, however the vast majority of pools would benefit from having a dynamic filtration schedule like this.
Low speed - 750 RPM = 22 GPM (96 Watts per hour)
Medium speed - 1400 RPM = 36 GPM (235 Watts per hour)
High speed - 2500 RPM = 71 GPM (950 Watts per hour)
The amount of time that you need to run your pump at low, medium and high speeds, as well as the actual RPM and flow rate you use for these speeds will be unique to your pool only. Every pool system is unique and with unique operational considerations. For most pools you should only need a few hours at high speed and then about double this amount of time at medium speeds. The remainder of the day is reserved for long hours of low speed filtration as this is where the bulk of your savings will come from every day.
Note that peripheral items like salt systems and heaters need consideration for flow, and you often hear people say how variable speed pumps are not good for this reason, but the reality is that RPM and flow needed for actuation of flow dependent devices like salt water take far less flow than you might think. After testing this theory I was able to determine that the most popular salt systems all turned on to operate with pump speeds much lower than anticipated. Take a look at this article that looks at the minimum RPM requirements for salt systems to operate: Pump RPM for salt systems
Filtration volumes
18 hours @ low speed - 22 GPM x 60 minutes x 18 = 23,760 gallons
4 hours @ medium speed - 36 GPM x 60 minutes x 4 = 8640 gallons
2 hours @ high speed - 71 GPM x 60 minutes x 2 = 8520 gallons
Water filtration total - 40,920 gallons (103% of target filtration volume)
Electrical consumption
18 hours @ low speed - 96 Watts x 18 = 1.728 kWh
4 hours @ medium speed - 235 Watts x 4 = 0.940 kWh
2 hours @ high speed - 950 Watts x 2 = 1.90 kWh
Power consumption total - 4.57 kWh
Total cost - 4.57 x $0.13 / kWh (national average) = $0.59 per day which is only $0.14 per 10000 gallons of water filtered!
It is worth repeating that every swimming pool system is unique with unique flow demands, resistance to flow, equipment, pipe size, choice of valves and orientation of fittings...this is how pool owners often get in trouble when they ask for advice about their pools. It is important to attempt to make fair comparisons about pools but in doing so it is also important to understand that not everyone is as good with their pool as they think they are. Take advice you get from non professionals with a hefty grain of salt when it comes to pools. If you want to learn more about how to design a functional pool filtration schedule then you can proceed to this article: Programming variable speed pool pump schedules.
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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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