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Variable Speed Savings For Small Pools

Variable speed savings for small pools
If you have a smaller swimming pool you might be wondering if there is any value in buying a variable speed pump for your pool. Do you still have the opportunity to save money versus just using a single speed pump and perhaps turning it off for part of the day since you do not need all that much flow volume daily? This article (and video) is going to break down this question in step by step detail to show you the difference in cost between single speed and variable speed specifically for small pools.

In this example we are going to be looking at a 12 x 24' pool with an average depth of four feet. This means that the pool volume is 8640 gallons. Following the industry standard of three turnovers of the pool volume being required every day for proper filtration this means you should be aiming for 25,920 gallons filtered every 24 hours. This would result in approximately 95% of the water in the pool being filtered at least one time. For this example we are going to compare a modestly sized 1.5 horsepower pump running four hours per day only versus a 24 hour variable speed pump schedule to see which is cheaper.

Pool width: 12'
Pool length: 24'
Average depth: 4'
Volume: 8640 Gallons
Filtration goal: 25,920 gal/day

If you only run your pump four hours per day this would result in 20 hours daily where the pool is sitting stagnant. This is far from ideal for chemical distribution and you would not be able to adequately run this pool with a salt water chlorinator, and possibly not with a heater either as both of these might well need more than four hours per day to operate. So it could be assumed this is a basic pool system without much in the way of frills or added peripheral items. Here is how the filtration totals for a 24 hour period can technically be achieved with a reduced four hour filtration schedule:

1.5 HP Single Speed Pump
108 GPM / 6480 GPH
2.3 kW per hour (6480 Gallons)
4 hours needed to reach 25,920 gallons
4 x 2.3 kW x $0.13 (nationwide average electricity cost)

= $1.21 per day
= $36.19 per month
= $3040.13 after 84 months

In the example above we are able to filter 25,920 gallons in only four hours time. The cost to do this would be 9.28 kWh of power, which multiplied by the nationwide average of $0.13 per kWh results in $1.21 per day to run the pump for four hours. At $36.19 per month it might not seem all that worth it to upgrade to a variable speed pump, but there is more than enough room for electrical improvement to justify the additional cost of variable speed, even on small pools.

1.5 HP Variable Speed Pump
1 Hour @ 3000 RPM / 90 GPM = 5400 Gal.
1 Hour @ 1500 RPM / 41 GPM = 2460 Gal.
22 Hours @ 500 RPM / 15 GPM = 19,800 Gal.
24 hour filtration total = 27,660 Gallons

1540 W/h @ 3000 x 1 = 1540 Watts
262 W/h @ 1500 x 1 = 262 Watts
63 W/h @ 500 x 22 = 1386 Watts
3188 Watts total every 24 hours

3.18 kW per day x $0.13 / kWh

= $0.41 per day
= $12.40 per month
= $1041.77 after 84 months

That is a total savings of $1998.36 after 84 months for the variable speed pump! Watch the video below to see it for yourself:

Even when you only run your single speed pump for a few hours per day this will still cost substantially more than running a 24 hour variable speed pump schedule with a similar total filtration volume. As you turn down the RPM of the pump motor there is a linear drop in flow rate but an exponential drop in power consumption. This is why turning off your pump can not possibly save you as much as using a well scheduled variable speed pump. As you can see in the numbers above a single hour on high speed moves 5000 gallons of water for 1500 Watts, but at low speeds the pump can move more than four times this amount of water for less total cost than one hour at high speed. The savings are stark, and most definitely you will save money with a variable speed pump, even on smaller swimming pools.

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.

Savings for a 20,000 gallon pool example

Swimming pool flow meters

Why don't more pools have flow meters?

How much power does a pool pump use?

Variable speed pool pump reviews

Swimming Pool Steve

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