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Variable Speed Pool Pump Savings

Variable speed pool pump savings
It can be confusing and overwhelming trying to calculate the potential savings with a variable speed pool pump. This is a calculation I make every day for pool owners however when you actually write out all of the steps involved in figuring out your electrical savings potential it becomes clear that there are actually quite a few numbers getting thrown around and it would be all too easy for someone to get overwhelmed, especially if solving a series of mathematical calculations is not your strong suit.

In this article I am going to make an apples to apples comparison between a 1.5 horsepower pool pump and the same sized variable speed pool pump. By defining the pool volume and using the same pump at 3450 RPM to represent single speed as well as variable speeds we can really level the playing field so to speak. For this example I wanted to use an "average swimming pool" so for these calculations this was for a 16' x 32' pool with an average depth of about five feet. This equals a pool volume of just about 20,000 gallons which is a nice, round number to work with for this example.

Pool width: 16'
Pool length: 32'
Average depth: 5'
Volume: 20,000 Gallons
Filtration goal: 60,000 gal/day

The goal with pool water filtration is that you want to filter all of your water every day. Due to the math behind water diffusion you require three turnovers of the pool volume to achieve 95% of the water in your pool being filtered one time. You can filter less if you choose to, but anything not filtered from your water will then need chemicals like chlorine to deal with, where you could have used mechanical filtration. In an age where most pool owners want less chemical exposure better utilization of the primary mechanism for removing debris from your water should be your first step in achieving this. You can filter your water less often, and you will "save" less money than a pool filtered much more, but you will also spend more on chemicals. No matter how much you choose to filter your pool water, you will still be able to filter that same amount of water more cost effectively with a variable speed pump than any single speed pump schedule.

1.5 HP Single Speed Pump
100 GPM / 6000 GPH
2.3 kW per hour (6000 Gallons)
10 hours needed to reach 60,000 gallons
10 x 2.3 kW x $0.13 (nationwide average electricity cost)

= $2.99 per day
= $90 per month
= $7560 after 84 months

In the example above the 60,000 gallon per day filtration goal is achieved by 10 hours per day of operation for the pump. During this time the pump is consuming about 2300 Watts every hour, during which time it is able to pump approximately 6000 gallons. After 10 hours the pump has moved the total filtration goal of 60,000 gallons, and the total electrical cost based on the nationwide overage of $0.13 per kWh of power consumption equals $2.99 per day to operate this pump and filter the pool water properly. With a variable speed pump you want to run the pump 24 hours per day instead of turning it off part of the day as this is the key to maximizing your savings. The pool only needs a few hours at higher speeds and a few hours at medium speeds to satisfy flow requirements for gas heaters and salt systems. The majority of your day could and should be at lower RPM operation.

1.5 HP Variable Speed Pump
3 Hours @ 3000 RPM / 86 GPM
6 Hours @ 2000 RPM / 55 GPM
15 Hours @ 1000 RPM / 28 GPM
1520 W/h @ 3000 x 3 = 4560 Watts
550 W/h @ 2000 x 6 = 3300 Watts
140 W/h @ 1000 x 15 = 2100 Watts
9.96 kW per day x $0.13 / kWh

= $1.29 per day
= $38.84 per month
= $3262.90 after 84 months

That is a total savings of $4291.10 after 84 months for the variable speed pump! Watch the video below to see it for yourself:

As you can see by changing to a variable speed pump with a 24 hour filtration schedule you are actually able to filter more water than with the single speed pump, and you are able to do so for considerably less money. $4300 less in this example based on a projected 84 month service cycle for the pump. It does not matter whether you live in a place where your pool runs 365 days per year or whether you live in a colder climate with a short swimming season...every month that you run your variable speed pump you are saving money. It will just take you longer to get to 84 months of operation. Also worth noting in this direct comparison between single speed pumps and variable speed pumps is that with the single speed the pool is siting stagnant 14 hours every day where the variable speed pump pool never sits stagnant, which is decidedly better for your pool.

The key to unlocking the savings potential of a variable speed pump boils down to a few key components. The first is a variable speed pool pump, next is understanding how a low and slow 24 hour filtration schedule with periods at medium and higher speeds is an advantage for you, and finally, the missing link is that you must buy and install a flow meter so you know how much water your pool filtration system is moving. This is critical to being able to get the maximum savings for your investment. Like a speedometer for a car, a flow meter tells you exactly how much water is moving through your system which you need to know in order to recreate the savings shown on this page in your own pool.

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Swimming Pool Steve

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