How Much Power Does A Pool Pump Use?
How much power does a pool pump use? In order to answer this in a meaningful way we need to break down the question further since there are many different types of pools and many different models of pool pumps. In general, swimming pool pumps are easily one of the worst offenders in the average home in terms of (wasteful) power consumption. The traditional method of water filtration for swimming pools, as employed for a half century or more, is woefully inefficient. How I normally answer the question of how much power does a pool pump use is by explaining that most home owners would never accept the level of inefficiency of a pool pump in any other appliance in the home.
It is simply a lack of knowledge about power consumption, flow rates and filtration requirements that results in this acceptance of an extremely inefficient electrical appliance...in some cases a pool pump can account for half of the electrical consumption for the home every month. That is a shocking statistic that highlights why the Department of Energy has determined that a nationwide change needs to take place to reduce the wasted electricity that has traditionally plagued the pool industry. While this news of rules being imposed that require pool owners to invest in more expensive and more efficient technology is not unanimously being received well, the reality is that pool owners should be happy. This is a cut and dry case of a new technology simply being leaps and bounds more efficient than previous versions of the same thing. Technology takes a while to catch on, and many people are resistant to change whether there is good reason or not to resist it. My experience is that the more you know about the numbers behind how all of this works the better you will be armed to make an informed decision for yourself. The more I researched variable speed pumps, flow rates and electrical consumption the more I am convinced that variable speed pumps are the best thing the pool and spa industry has seen in decades.
Single Speed Pool Pump Power Consumption
The first thing you need to learn about when we start to look at the potential for efficiency improvements with your swimming pool pump is how much power a traditional single speed pump consumes. The answer to this depends on the size of your pump, the piping configuration and size for your pool, the quality of your filtration system...the lest goes on and on. While the actual electrical consumption and associated flow rates for a given pump on your pool will be unique to only you, I think you will find a great deal of value in seeing an example of a "common" size of pool pump.
Pool pumps range in size from 1/2 horsepower up to 3 horsepower (or more, less commonly) and the size of your pump will determine how much power it consumes. This is the greatest fallacy in the pool and spa industry. For decades pool owners have been shopping for pool pumps based on horsepower with the traditional mindset being that more is better. The horsepower rating for pumps, which is specifically misleading due to power factor ratings from pump manufacturers, is simply an indication how much it costs to run the pump. So buying a pump with more horsepower serves only to increase the price that you pay per hour to run it. Worst of all, and something that so few pool owners appreciate, is that a 1 horsepower or 1.5 horsepower pump is already oversized for a filtration system. Increasing the horsepower serves to further increase your system inefficiency, and even can also compromise and damage other components like your filter.
A well sized and true rated 1/2 horsepower pump, perhaps a 3/4 horsepower would almost universally be a better, more efficient option, for your pool filtration pump. This is because horsepower tells you nothing about how well a pump will filter your water. What is very relevant is how much flow do you actually achieve. Pool filtration should be based on flow rates and you want the lowest horsepower possible that still meets the flow rate requirements that you need. By the book you should filter the volume of your pool three times every 24 hours. If you have a 20,000 gallon pool then you need to filter 60,000 gallons every 24 hours. If you ran you pump around the clock that would be 2500 gallons of water filtered every hour. Broken down further that is 41.66 gallons per minute of flow.
This is the point where a straight forward conversation starts to go off the rails. Some people do not follow the recommended standard of three turnovers of the pool volume daily. Many pool owners use a single turnover, or even less than that. The reason why this happens is because pool owners do not want to pay more than they need to for electricity. This is how cost of operation has changed the industry (for the worse) since pool owners started to measure the filtration of the water based on hours of pump operation and not volume of water filtered. Looking at the values from the video example above we can see that a 1.5 horsepower pump running at 3450 RPM, installed with a 240 volt electrical service, running on a minimal 1.5" plumbing system was able to achieve about 82 gallons per minute of flow while consuming 2.24kW of power doing so.
How Much Does It Cost To Run A Pool Pump?
If you want to know how much it costs you to run your pool pump then you need to know the electricity rates that you pay. Somewhere on your electricity bill you will see a "per kWh charge" which should be how many cents you pay for each kWh (kilowatt hour) of electricity that you use. If you are not familiar with these terms it is actually very easy to understand. Power is measured in Watts, and you can calculate Watts by multiplying Voltage (in Volts) by the Current (in Amps). Some common examples you might already know would be something like a 100 Watt light bulb. A 100 Watt light bulb uses 100 Watts of power continuously. Another way of saying the same thing as 100 Watts is 0.100 kW. A kilowatt is 1000 Watts, so our 100 Watt light bulb could also be called a 0.100 kilowatt light bulb. If you ran it for one hour, then you would have used 0.100 kWh (kilowatt hours). Likewise if you had a giant 1000 Watt light bulb, or a 1 kW light bulb, running it for an hour would result in, you guessed it, 1 kWh of power consumption.
Now that you have seen an example of what a kilowatt hour is, and how you calculate kWh for electrical appliances, you now need to know how much you pay for your electricity. Shown in this video example are common electricity rates, current for late 2019, however this is only the tip of the iceberg for calculating pool pump costs. Most areas have now switched to a variable electrical rate schedule which changes the kWh rate that you par based on the time of day the power is being consumed during. Taking advantage of the variable cost of electricity is something that I will cover in greater detail at a later point so for now you can consider electrical rates to be static as opposed to variable. Once you have a solid understanding for how to calculate costs and compare these to flow rates you will be able to take it to the next level by looking at the potential for programming your variable speed pump to benefit from the maximum possible electrical savings.
Do Two Speed Pumps Save Electricity?
A single speed pump moving water at 3450 RPM has a lot working against it when it comes to efficiency. This is why two speed pumps, or dual speed pumps, exist within the market. Before the technology was available to have complete control over the RPM of your pool pump motor there existed two speed pumps. These pumps could run at full speed, 3450 RPM, just like a single speed pump, but in addition to this the pump could be switched to run at half, at about 1725 RPM. This is very significant in terms of the potential for electrical savings. As discussed in this article about how variable speed pumps save you money you can see that as the RPM of the motor is reduced, there is a non-linear drop in the power consumption of the motor.
In this video a two speed pump is being simulated to show you what happens to the electrical consumption and flow rates for a pool pump when you cut the motor RPM in half. This pump as displayed in the video at the top of the page was able to move 82 gallons per minute of water while consuming 2.24 kW of power, running at full speed 3450 RPM. When the RPM value was reduced to 1730, just over half speed, the power consumption dropped drastically to only 360 Watts, or about 0.36 kW. While the flow rate dropped as well the system was still able to achieve 38 gallons per minute. From this example we can see that there was nearly a linear drop of flow, where the electrical consumption dropped by six times!
Flow Rate = 82 GPM
Power Consumption = 2240 Watts
Cost per hour (based on 13 cents per kWh) = $0.29
Flow per hour = 4920 Gallons
Cost per 24 hours = $6.96
Flow per 24 hours = 118,080 Gallons
Flow Rate = 38 GPM
Power Consumption = 360 Watts
Cost per hour (based on 13 cents per kWh) = $0.047
Flow per hour = 2280 gallons
Cost per 24 hours = $1.13
Flow per 24 hours = 54,720 Gallons
As soon as you start to look at the numbers behind flow and cost for pool filtration it starts to become obvious that there is an efficiency discrepancy. Water moves more efficiently at slower speeds, as well as electric motors using far less power at lower speeds than they do at higher speeds. There is no doubt that two speed pumps save electricity but the real question with them is and has always been whether the two speed options are useful for your specific pool. If you have a very basic pool then a dual speed pump can pretty much replace your single speed pump successfully. On robust pool installations with in-floor cleaning systems, water features, attached hot tubs or any other high flow demand items a dual speed pump may not work as well. Thus is the limitation of two speed pumps and their usefulness in the field. If you were lucky enough that you could use one then it really could, and can, save you money.
What if you had a pool heater that needed a lot of flow in order to fire up and run, but a dual speed pump running on low speed was not enough flow for the heater to work? Well in this situation then you would have to run the pump on high speed any time you want the heater to work. It is this limitation which is most completely solved by new variable speed pump technology. A well tuned pool system can be such that you program you pump to run at the minimum necessary speed in order for each of your pool devices and peripheral items to work properly. A two speed pump was our first peek at utilizing RPM speeds to reduce the total electrical cost for a pool system to run. It had limitations but the pools that could work within those limitations were able to run for far less than those using only a single speed pump.
Advantages Of Variable Speed Pumps
As shown with the above examples single speed pool pumps move a lot of water but not very efficiently. Dual speed pumps move water way more efficiently, gallon for gallon, however they do so at an overall slower rate than single speed pumps so they need to run longer to achieve the same filtration...but that is okay since running the pump at a lower speed might move less water, but is also uses less power - way less. The down side of two speed pumps is the limited application for them. Pools that can get away with running at half speed benefit for sure, but dynamic pools or pools with heavy flow demands probably do not benefit as much from a two speed pump since the low speed is not enough to run the peripheral devices that the pool has installed.
Enter variable speed pumps into the equation. Variable speed pumps are the best of both worlds in that they can cost less to run, but also have the adaptability to dial in the exact RPM and flow rates that your unique pool needs. This allows every pool to be as efficient as possible limited only by the design and features that the pool has. No matter what RPM you need, and associated flow rate, in order for your heater to run you will be able to program that exact value into your pump. This allows you to run everything that you need to run, all without running the motor of the pump at any higher RPM than is absolutely necessary. There is so much benefit in lowering the RPM of your pump, but now no matter what your flow rates are, or need to be, you will be able to achieve those with a variable speed pump. Just be sure you take to time to learn about programming your pump and having a schedule that meets your filtration needs and flow rates for all the peripheral devices that you have. To learn more about this read this article about variable speed pump schedules.
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