Optimal regime for variable-speed pump?

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aloneinca

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Apr 29, 2014
6
Sunnyvale, CA
My variable pump's power consumption is very non-linear by RPM. It takes around 300W at 1500RPM and over 2000W at max 3250 RPM. If the relation between circulation and RPM is linear, my best bet would be running it at lowest RPM/Watt ratio. Could someone confirm/deny my theory.

Also, how do I calculate the running time? I see the article from the University but it has no specifics. I remember reading somewhere that I need to circulate the whole pool in a day.

I had algae issues in the past, possibly due to water contaminated with elements/too high CYA after misuse of tablets. Now I am restarting the pool after replastering/refilling. Typical water temp. in the summer is 80-85F. I am trying to keep chlorine at 3PPM. Use DE filter running on cellulose. I cover the pool and my cleaner robot keeps it pretty clean. Installed salt chlorinator/ph balancer and will start using it in a couple if weeks.

Thanks for any suggestions.
 
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aloneinca said:
My variable pump's power consumption is very non-linear by RPM. It takes around 300W at 1500RPM and over 2000W at max 3250 RPM. If the relation between circulation and RPM is linear, my best bet would be running it at lowest RPM/Watt ratio. Could someone confirm/deny my theory.
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It takes more than twice the power to spin at twice the RPM, and it takes more than twice the RPM power to pump at twice the rate. So low speed for a long time is more efficient than high speed for a short time.

[Edit: "RPM" -> "power". I shouldn't post at 1:30am.]
aloneinca said:
Also, how do I calculate the running time? I see the article from the University but it has no specifics. I remember reading somewhere that I need to circulate the whole pool in a day.
Click to expand...

Circulating the entire pool volume ("turning over" the pool volume) every day isn't actually necessary. Only a couple of things are important:
  1. For the processes that are powered by water flow (your cleaner and your saltwater chlorine generator), you need to run the pump at the RPM that those processes require, for as long as they require.
  2. You need to run the pump at sufficient RPM and for enough time for your skimmer(s) to keep the surface of the pool clean.
Filter pumps are designed for continuous operation, so don't hesitate to run yours 24 hours/day at a super-low RPM if that will keep everything working. You saw 300W at 1500RPM, but the pump might draw under 100W at 1000RPM -- and even here in the Bay Area, a continuous 100W draw costs less than $1/day.

aloneinca said:
I am trying to keep chlorine at 3PPM.
Click to expand...

If you follow the TFP methodology, you'll probably want to maintain CYA at 70-90 and free chlorine at around 6ppm. See Pool School.
 
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DrewLG said:
It takes more than twice the power to spin at twice the RPM, and it takes more than twice the RPM power to pump at twice the rate. So low speed for a long time is more efficient than high speed for a short time.

[Edit: "RPM" -> "power". I shouldn't post at 1:30am.]


Circulating the entire pool volume ("turning over" the pool volume) every day isn't actually necessary. Only a couple of things are important:
  1. For the processes that are powered by water flow (your cleaner and your saltwater chlorine generator), you need to run the pump at the RPM that those processes require, for as long as they require.
  2. You need to run the pump at sufficient RPM and for enough time for your skimmer(s) to keep the surface of the pool clean.
Filter pumps are designed for continuous operation, so don't hesitate to run yours 24 hours/day at a super-low RPM if that will keep everything working. You saw 300W at 1500RPM, but the pump might draw under 100W at 1000RPM -- and even here in the Bay Area, a continuous 100W draw costs less than $1/day.



If you follow the TFP methodology, you'll probably want to maintain CYA at 70-90 and free chlorine at around 6ppm. See Pool School.
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Thanks for your response! I will maintain these levels when I get salt going.

But I am a bit confused: if I don't run cleaner (I use electronic robot), don't have salt yet and have clean surface (since I cover the pool), I don't have to run the pump at all? There has to be a way to estimate the boundary here?
 
aloneinca said:
if I don't run cleaner (I use electronic robot), don't have salt yet and have clean surface (since I cover the pool), I don't have to run the pump at all?
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Well, the need is substantially reduced. But you will probably want to run the pump for an hour or so anyway, to distribute the chlorine that you'll be adding while you wait for salt, and to filter particles out of the water and keep it from stagnating.

At some point, though, you'll want to swim in the thing. And to do that, you'll have to open the cover and let the surface get dirty and require skimming. So yeah, you can save a little energy by optimizing your pump schedule for the current unusual condition -- but if that condition isn't going to last very long, maybe make it easy on yourself and just set the schedule now for the runtime that the pool will need once salt is in it. You can estimate or measure the FC loss per day, and Pool Math can tell you how long you'll need to run your SWCG in order to regenerate that lost FC.
 
DrewLG said:
Well, the need is substantially reduced. But you will probably want to run the pump for an hour or so anyway, to distribute the chlorine that you'll be adding while you wait for salt, and to filter particles out of the water and keep it from stagnating.

At some point, though, you'll want to swim in the thing. And to do that, you'll have to open the cover and let the surface get dirty and require skimming. So yeah, you can save a little energy by optimizing your pump schedule for the current unusual condition -- but if that condition isn't going to last very long, maybe make it easy on yourself and just set the schedule now for the runtime that the pool will need once salt is in it. You can estimate or measure the FC loss per day, and Pool Math can tell you how long you'll need to run your SWCG in order to regenerate that lost FC.
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Appreciate the insight
 
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