Running A Pool Pump 8 Hours Per Day
You run your pool pump eight hours per day and you want to know more about how much this is costing you, and more importantly, could a variable speed pool pump help you to reduce on your electricity costs. In an attempt to answer this question we will look at a real life bench test of a 1.5 horsepower Pentair Superflo variable speed pump. Since every pool installation is completely unique it would be difficult to mirror your exact situation. Using a 1.5 horsepower pump for this test is a good "middle of the road" pump size which should provide some relevant data to review. It is however important to understand that this is just a bench test environment, and the actual flow rates and electrical consumption that you would experience on your pool will be unique. This is purely an illustration to give us a starting point where we can review some numbers to determine the viability of a variable speed pump versus a single speed pump of similar size that you elect to run for 8 hours per day.
If you run your pool pump for eight hours per day, how much water are you able to filter during this time? If you are unable to answer this question, then you will also be unable to determine the viability of a variable speed pump. The critical piece of information that is missing from most pools is the amount of water that your pump is moving at any given time. Without a measure of the flow volume it would be impossible to prove the effectiveness of a variable speed pump. This is why it is critically important that you invest in a flow meter for your plumbing system as this will allow you to dial in your flow rates exactly, removing all of the guess work from filtering your pool water...not to mention being able to save the most money from correctly programming your variable speed pump. For more information you can read this article about swimming pool flow meters.
The bench testing for this pump is based on a very simple and low head (resistance to flow) plumbing system with minimal suction and return lines. If you have multiple suction and return lines, and especially if they are 2" or larger in size, then you should see even greater flow rates than what you see here.
Example 1.5 HP Single Speed Pool Pump
RPM - 3450
Power Consumption - 17.92 kW (2.24kWh x 8)
Flow Rate (2" and 1.5" pipe) - 90 GPM
8 Hour Running Cost (@ $0.13 / kWh) - $2.33
8 Hour Filtration Total - 43,200 Gallons
Again, understanding that your numbers will surely be different than these exact figures, they should be within a tolerance such that this information is still specifically useful to your savings calculations. From the above information we can see that every day you filter approximately 43,200 gallons of water. The cost that you pay is roughly $2.35. For the electrical cost, if you happen to know the electrical rates that you pay per kWh then you should use those in place of the $0.13 multiplier I used here which represents the nationwide average. Also worth noting is that you might (probably) have variable electrical rates based on the time of day, and if you run your pump for 8 hours in the middle of the night, you might be paying less than $0.13 per kWh, which would also be important to know if you want your numbers to be as accurate as possible. For the purposes of this example I want to keep it as simple as possible, which is why the 13 cents average cost per kWh is being applied.
Advantages of variable speed pumps - So in this example the variable speed pump would need to be able to filter at least 43,200 gallons every 24 hours, and it would need to do so for less than $2.33 in order to provide a return on investment. This is the crux of the situation. Again this is a more dynamic equation than I can present here since each pool is different. If you have an electric heat pump, or salt water, or an in floor cleaning system, or a pressure side cleaner that runs from your filtration pump...all of these would change the way that you program your variable speed pump. To learn more about how to design a variable speed pump filtration schedule that meets the needs of your pool then you can read this article about programming your variable speed pump.
High Speed Operation
Motor RPM: 3000
Duration: 2 hours
Power Consumption: 3.01 kW (1.51kWh x 2)
Flow Rate: 77 GPM (4620 GPH)
2 Hour Running Cost (@ $0.13 / kWh): $0.39
2 Hour Filtration Total: 9240 Gallons
Medium Speed Operation
Motor RPM: 1750
Duration: 6 hours
Power Consumption: 2.23 kW (372Wh x 6)
Flow Rate: 43 GPM (2580 GPH)
6 Hour Running Cost (@ $0.13 / kWh): $0.29
6 Hour Filtration Total: 15,480 Gallons
Low Speed Operation
Motor RPM: 1000
Duration: 16 hours
Power Consumption: 2.14 kW (134Wh x 16)
Flow Rate: 18 GPM (1080 GPH)
16 Hour Running Cost (@ $0.13 / kWh): $0.28
16 Hour Filtration Total: 17,280 Gallons
In this "real world" variable speed pump schedule we have allotted two hours near maximum speed to allow for pressure cleaners or other high flow rate items that might need to operate daily for the pool. There is also a six hour period at medium speed to allow longer periods of operation for things like salt water systems or electric heat pumps which require more than the minimum RPM in order to turn on and function safely. Finally there is a 16 hour period where the pump runs at a relatively low RPM setting. These long hours at low speeds, and low electrical costs, are where you make your real savings with a variable speed pump. You just need to determine how much flow the peripheral items in your pool need, and then program the pump to run at those speeds.
Example 1.5 HP Variable Speed Pool Pump
24 Hour Power Consumption: 7.38 kW
24 Hour Running Cost (@ $0.13 / kWh): $0.96
24 Hour Filtration Total: 42,000 Gallons
In total the variable speed pump was able to reduce total electrical consumption by 60% while filtering the same total volume of water every day. At $1.37 in savings every day, that would be about $41.10 per month, or $493.20 per year. Variable speed pool pumps are rated to operate for seven years before they should require service, and projecting using that (very achievable) number would give you a potential savings total of $3452.40. That is an incredible and absolutely undeniable number, a significant savings, over and above an eight hour filtration schedule which is technically already a lean "energy saving" filtration schedule for a swimming pool.
There are two common objections that are brought up a lot when you start talking about variable speed pump savings. These are valid arguments if you present them correctly. The first is that variable speed pumps are more expensive, yes, but people often quote them as being thousands of dollars that they need to recoup in electrical savings. The pump used in this exact example currently sells for $729 where the single speed version of this same pump is $428 which means the difference in price is only $301. You can look at the current prices here. So in total you need to save $301 to make this pump worth the investment, and not thousands of dollars. Next, many pool owners live in a seasonal area where the pool does not operate year round. This does nothing to diminish the returns that you will get, it simply means it will take longer to recoup the exact same electrical savings, but also assumes that your pump will be in service twice as long as a pump that runs 365 days per year. I break this down further if you would like to read more about variable speed pumps on seasonal pools.
If you are convinced then take a look at these popular variable speed pump reviews
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