What Is The Cheapest Way To Filter Pool Water?
The daily filtering of your swimming pool water represents the largest cost component of owning and maintaining a swimming pool. You might think it would be the chemicals that you use making corrections to your water chemistry however you might be surprised to learn that swimming pool pumps (used for filtration) can account for up to half of the power used in your home every month. Not every pool will cost this much, but if you are a pool owner who runs their single speed pump 24 hours per day then this might be exactly the situation you are in. While most people with swimming pools elect to install timers to operate the pump less often there are still many who simply leave the pump running constantly.
The real question here is "how much are you supposed to filter pool water?" and the answer to this is surprisingly simple...you are supposed to filter all of your pool water, every day. What starts as something that sounds straight forward enough becomes more complex right away when you consider that filtering all of your water is actually harder than you first think. If you have a 10,000 gallon pool then you can not simply pump 10,000 gallons through the filter and get "all" of your water filtered. In fact doing this, pumping a single "turnover" of your pool volume would only net you about 63% of all the water in your pool being filtered. As filtered water returns to the pool it diffuses within the unfiltered water which means you get less and less unfiltered water with each turnover of the pool volume. After three turnovers you will have effectively filtered 95% of the water in your pool. After four turnovers you would have achieved 98% of all water. Two turnovers only nets 86% of the pool water, so either three or four turnovers daily should be your goal. For most residential pools three should be sufficient.
Pool filtration requirements - If you have a 10,000 gallon pool you need to filter 30,000 gallons per day. If you had a single speed pump that moves 65 GPM (3900 GPH) then you would only need to run that pump for 7.9 hours daily to meet your 24 hour filtration goal. With new energy saving variable speed pool pumps you would go about this differently in that you would take 30,000 gallons and divide by 24 to determine that you only need 1250 gallons per hour, or 20.8 GPM in order to reach your daily filtration goals.
Flow rates for pool equipment - It would not be a good idea to filter your pool only on low speed (1250 GPH) as there are peripheral items which require more flow than this. Yes you would achieve enough total filtration volume daily however pools also need periods of time with the pump running at higher speeds. The skimmers in the pool require a fair bit of flow in order to pull debris and leaves from the surface of the pool. Gas heaters and electric heat pumps need reasonably strong flow in order to operate, as well as other peripheral items like ozonators, salt water chlorinators and erosion feeders. A properly balanced 24 hour pool filtration schedule should include a few hours at high speed for heavy flow demand items to operate, as well as a few hours at medium speeds for mid range items like salt chlorinator units to function. The remainder of the 24 hour schedule should be at minimum speeds for maximum savings on your filtration.
Every pool is unique and the amount of flow and hours of operation for your pool systems needs to be tailored individually. There is no getting around this fact. Even if you had two pools with the same equipment you still would need to set the pump RPM and flow requirements for peripheral equipment individually. Every pool is built differently and everything from pipe size, fitting selection and orientation, elevation of the pool, elevation of the equipment, distance between pool and equipment...all of these will change the total dynamic head of head (resistance) of the plumbing installation. Where 1500 RPM might equal 30 GPM with one system it might be 20 GPM or 40 GPM with a different swimming pool that looks "almost identical". These are very important details and it makes it hard for pool owners looking for generic information about what speed to program their variable speed pump. You need to be able to monitor the flow rate for your pool system in order to know what RPM to set your pump.
How to reduce pool filtration costs
You could turn off your pump for part of the day to cut costs but this would actually cost you in terms of lost potential savings. If you only have a single speed pump then turning it off for part of the day makes sense...it is the only way in which you have to avoid over-paying (and over filtering) your pool water.
Once you get a variable speed filtration pump, which you definitely should, you will want to run your pump 24 hours of the day taking advantage of as many hours of low speed operation for your pump as possible. You still need to have hours at higher pump speeds but the long hours on low speeds are where your super-low cost filtration comes from. As you turn down your pump speed you have a linear drop in flow rate along with a non-linear drop of power consumption. The lower your speeds the lower the cost (per gallon) to filter the water. In order to do this properly you need a variable speed pump and a flow meter.
Pentair SuperFlo Variable Speed Pump
Hayward MaxFlo Variable Speed Pool Pump
Hayward TriStar Variable-Speed Pool Pump 1.85 HP
Pentair IntelliFlo Variable Speed Pool Pump
H2 Flow Controls FlowVis Flow Meter (2" & 2.5")
H2 Flow Controls FlowVis Flow Meter (1.5")
Blue-White Swimming Pool Flow Meter (2")
Blue-White Swimming Pool Flow Meter (1.5")
With a variable speed pump along with a flow meter you can program a 24 hour filtration schedule that uses periods of time at medium and higher speeds combined with long hours at low RPM operation. For low speed operation simply install the flow meter and variable speed pump and start at the lowest speed and increase in small increments until you are able to register flow on the lowest end of your flow meter spectrum. At such low speeds it is hard to tell if the pump is even moving any water at all, which is why you need the flow meter. As seen in the video above flow that is very low, too low to register movement by eye or feel, is enough to get over 50,000 gallons per day through the filter. THAT is the cheapest way to filter your pool water.
Variable speed pump 24 hour schedule programming
Breakdown of total savings from a variable speed pump
Flow rates for different RPM speeds examples (1.5 HP pump)
How much power does a pool pump use?
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