Efficient Pool Plumbing Design
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There are probably a thousand decisions you can make when designing or building a swimming pool that will impact the potential for efficient operation. When you hire a pool contractor to build a pool for you it is likely that you are being pitched a design that will maximize profits and minimize difficulty for the builder. If you want the most efficient pool possible then this is something you are going to have to ask for, advocate for even, as well as paying a higher upfront cost in most cases. But would you not spend an extra $1000 if it meant you would save $5000 in the long term? Well, that is pretty much the exact case with variable speed pump savings potential so I think we have just figured out the number one thing on this list that you can invest in now for your pool design so that you can reap the rewards in the future.
Choosing a variable speed pump versus a single speed pump should be so much of a slam dunk, no-brainer by this point it is hardly worth mentioning in some circles...but not all pool owners are as informed yet. So many pool owners still have a single speed pump that gets terrible energy efficiency instead of upgrading right here and right now to a variable speed pump. If they make a new Honda Civic tomorrow that gets a million miles per gallon, then I want to own it now. I am not going to drive my old Honda Civic getting 32 MPG for five more years when upgrading now will save me more than the cost of the car payments just in gas savings alone! That is the figurative comparison we are making here. Don't wait until your single speed pump dies of natural causes. Replace it and start saving money today.
Pipe Size For Efficient Pool Filtration
Most likely the size of the plumbing used to build your swimming pool will mean the difference between night and day in terms of flow efficiency. This is an important consideration especially since with a variable speed pump it will be important to run your pump around the clock 24/7 to get maximum savings.
If you have the wrong size pipes on your pool that means that your system is running inefficiently 24 hours per day. Getting more specific, fast moving water moves inefficiently due to friction, turbulence, resistance to flow of all kinds. If you force water to move fast like this you experience a sharp efficiency loss above six feet per second of water velocity.
Conversely, water moving slowly and with laminar flow (no turbulence) does so very efficiently as there is almost no friction or resistance to flow. When designing a pool system you want to determine the total flow rate you will need for filtration. This could be three times the volume of the pool filtered every 24 hours, as this represents about 95% of all the pool water being filtered at least one time. If we use 20,000 gallons as an example pool volume, then you would estimate 60,000 gallons as a daily total for filtration. We can then use this to reverse engineer the flow rates we might need:
20,000 gallons x 3 = 60,000 24 hour filtration goal
60,000 / 24 = 2500 gallons per hour
2500 GPH / 60 = 41.67 gallons per minute
So from this quick and rough calculation we can see that 24/7 of running the pump at just under 42 gallons per minute will give us the 60,000 gallons per day filtration goal we want. So how does this apply to pipe size? Well, you can reference what six feet per second of flow velocity will achieve in gallons per minute in this article about pool pipe sizing you can see that some of the most common pipe sizes for swimming pool systems:
1.25" pipe = 28 GPM
1.5" pipe = 38 GPM
2" pipe = 63 GPM
2.5" pipe = 90 GPM
3" pipe = 138 GPM
4" pipe = 238 GPM
Looking at this info we can see that the 1.25" pipe normally associated with above ground pools would be too limiting. Also the 1.5" pipe commonly associated with older inground pools, smaller inground pools and generally inefficiently designed pools is too small as well. Only 38 GPM of efficient flow would not be enough to filter this pool sufficiently. I mean, sure it could filter the water by increasing the flow rate, but now your flow is no longer efficient. Once we get to the 2" pipe you can see that we can now achieve the 42 GPM that we need to filter this pool to the "minimum" degree. So it can be said that 2" pipe is what you want to use to build this pool. It is worth considering that going up one more size might be a good idea as this means we could have as much as 90 GPM under laminar, efficient flow.
Pipe Size For Efficient Filtration
This is an important takeaway in that you do not want to run your pump at one low speed 24 hours per day. You need to have periods of time at higher speeds, periods of time at medium speeds, and then the rest of the day at low speeds for long hours of cost effective filtration. It would be great if you could even have periods of time at high speed and high efficiency. This way you could have ALL of your 24 hour operation within the limits of laminar and efficient flow. This would be ideal, but there is a point of diminishing returns for oversizing plumbing both in terms of cost of installation material and line size valves but also in terms of performance.
It is also worth noting that there are very important safety considerations relating to flow as well, and you must not exceed the flow rates that your skimmer and main drains are rated for. Truly this is just scratching the surface of how to design a pool system efficiently and is not a fully comprehensive look at how to size your plumbing but it should give you some context as to why pipe size matters so much and what you might be leaving on the table in terms of efficiency by undersizing your plumbing system.
Efficient pool plumbing systems take advantage of laminar flow to limit friction and turbulence and oversizing of the plumbing can dramatically increase the maximum efficient flow rate, but also just the maximum flow rate in general. This is actually very important as you must factor in the maximum flow rate for any and all equipment installed on the equipment pad. Starting with the filter, sand filters have notoriously low maximum designed flow rates that you should never exceed. Oversizing your plumbing system would give even a moderate pool pump the ability to meet and far exceed the max flow rate for most sand filters, even larger ones. DE and cartridge filters are much better for having high maximum flow rates in general. Similarly you should also know the max flow rate for any peripheral devices like AOP, UV lights, heaters, and pretty much anything that has water running through it. Your potential to overdrive your equipment increases when you increase pipe size so that is why you must have a full understanding of how to install the equipment safely and properly. This is also one of the reasons it is so important to install a flow meter in order to monitor the rate of water movement through your system at all times.
To see some examples of common pipe and fitting selection issues when installing pool equipment be sure to check out the 50 part video series on pool equipment installation reviews that you can find here: pool equipment installation tips.
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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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