Running A Pool Pump 4 Hours Per Day
This article is intended to look deeper into the situation where you have a swimming pool but you only run your filtration pump for four hours every day. Many pool owners elect to run their filtration pump less than 24 hours per day since most pools would not need that much filtration to operate, and excess filtration of the water is not cost efficient. Running a pool pump can certainly be expensive as highlighted in this article about how much electricity does a pool pump use?. In an attempt to reduce the (significant) operating costs associated with running a pool pump motor around the clock most pool owners have traditionally installed a mechanical 24 hour timer that automatically turns their pump on and off at a specific time every day. The only other option than this was to install a two speed pump which could potentially reduce your pump power consumption if you had a pool that was suitable for a two speed pump.
Forging ahead the pool industry has turned to a new technology for filtration systems - variable speed pumps. Variable speed pumps build on the concept of a two speed pump but further enhance the functionality of the pump which makes variable speed pumps suitable for almost any pool installation. Two speed pumps while potentially more cost efficient were limited to having either low speed or high speed and not all pools could function well on the flow rate generated from the lower speed setting. With a variable speed pump this is no longer an issue as you simply dial in the correct motor RPM and associated flow rates to meet the needs of your specific installation. The technology of RPM control has the end result of vastly reducing electrical consumption while still maintaining enough filtration and flow for the pool. Some pool owners however are still not convinced that switching to a variable speed pump is really worth it.
The conventional argument against getting a new variable speed pump is that "I only run my pump four hours per day" so there is no point in getting a variable speed pump. The reality is that this is flawed logic. Running a pool pump for a few hours per day was invented by cheap pool owners to save money. The cost of operation, in reality, has nothing to do with how you clean and filter pool water. Choosing to ignore all of the conventional wisdom and established industry best practices for how a filtration schedule is calculated is, at best, a poorly vetted decision. That is the same thing as saying "I only change the oil in my car every 100,000 miles because oil changes cost too much money". If you feel offended hearing this then by all means run your pool pump for four hours per day. I genuinely appreciate that not all people will see value in doing things by the book. If you want to run your pump for twenty minutes per day then go for it. This information is primarily intended for pool owners who have heard about this reduced running schedule business but are skeptical that this is actually a good idea. It's not. Water quality and clarity depend on filtration. Filtration requirements are determined by pool volume. You might not have an issue, or at least any issues that you are aware of, when running your pump only four hours per day...but you are taking a health and safety risk in the interest of putting a few dollars back in your pocket. Not very heroic when you put it like that. Especially when there are better options that cost less and do not require that you short-cut your filtration schedule just to save money.
With 4 hours of running time you are NOT meeting minimum filtration standards - Running your pool pump for 4 hours per day means that you will have stagnant water 20 hours out of each day. You will also likely not be meeting minimum established filtration standards. This is where the low-and-slow approach to variable speed pumps really puts single speed pumps to shame. Variable speed pumps are supposed to run all day long, albeit at much lower RPM's than a single speed pump. This means that you can run your pump 24 hours per day and experience no times where the water is sitting stagnant. Best of all you can filter more water this way while spending less money overall on electricity versus a single speed pump. Still, there is no one size fits all solution to filtration of swimming pools and that is why we need to look at more than just hours of running time when it comes to water filtration.
Example 1.5 HP pool pump
RPM - 3450
Power Consumption - 2.24kW (2240 Watts)
Flow Rate (1.5" pipe) - 82 GPM
4 Hour Running Cost (@ $0.13 / kWh) - $1.16
4 Hour Filtration Total - 19,680 Gallons
In this example we look at a 1.5 HP pool pump running on maximum speed, 3450 RPM, while installed on a 1.5" plumbing system. Under these bench test conditions we were able to achieve 82 gallons per minute of flow, while consuming 2.24 kW of power. Your pool system is unique and your flow rates and electrical consumption will differ slightly from these numbers. Additionally there are many different models and sizes of pumps, each with their own unique hydraulic efficiency. This testing simply looks at a very common situation of a 1.5 horsepower pump running on 1.5" pipes.
Importance of turnover in pool water - Your swimming pool water needs to be filtered every day. In order to filter "all" of your pool water you actually need to pump more than the volume of your pool. This is because your pool water does not all line up nicely and wait to be filtered. If you have a 20,000 gallon pool and you pump 20,000 gallons through your filter then you have not actually filtered all of your water. Some has been filtered twice or more, some has not been filtered at all. In order to filter 98% of your water you need to actually pump the volume of your pool three times. Four times would bring you into the 99 percentile but three times is often viewed as an acceptable minimum value for filtration. In the above example, if you have a 20,000 gallon pool then you would have achieved less than a single turnover of water in your pool. If you want to risk making someone sick, or worse, as well as using more chemicals than you need to, then by all means filter your water less than you should.
When you care about your pool and your bathers then you need to achieve at least three turnovers of water every 24 hours in your pool. In the above example this means that you would want to actually filter 60,000 gallons of water or more every 24 hours, and running the pump only four hours per day simply will not cut it. For a very simple comparison look at these numbers from a variable speed pump running on the exact same system but this time at half RPM value:
Example 1.5 HP pool pump
RPM - 1730
Power Consumption - .360 kW (360 Watts)
Flow Rate (1.5" pipe) - 38 GPM
24 Hour Running Cost (@ $0.13 / kWh) - $1.13
24 Hour Filtration Total - 54,720 Gallons
The takeaway here is that without making any effort to dial in the RPM values for this pump, and simply by running it at half speed you can already see a substantial improvement over running the same pump at full speed for four hours per day. In this example we ended up spending almost exactly the same amount of money on electricity every 24 hours, but with the variable speed pump we were able to filter almost three times as much water, and at no point was the water in the pool left to sit stagnant. Yes in a real pool situation the pump should probably run at higher than half speed for at least part of the day, but in the same light we also can do much more to further reduce electrical costs by running the pump, at least part of the day, at an even lower RPM than the 1730 RPM that we tested. In total, you spend less while getting more filtration and best of all - you do not compromise the quality of your pool and swimming experience simply to try to save a few dollars.
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