Save electricity with a 2 speed pool pump

[gtojohn]

Great website, I'll try to contribute with what I know.
Swimming pools are awesome, but their upkeep requires a lot of power. Most pools are built with over sized pumps that use more power and waste energy because of head pressure and pipe resistance. For instance I have a 10,000 gallon pool it is common to see builders match up 1.5 hp motors for this size. I currently run a 3/4 hp pump that moves enough water for 4 return jets to break the surface of the water or move back the pool cover. In theory because I'm moving half water than the 1.5 hp I would need to double my run times. In practice I get by running the pump intermittently for 4 hours a day.

My current project is to replace my single speed 3/4 hp with a 2 speed 3/4. Low speed is 1/2 the rpm and flow but uses 1/8 electricity. This reduction is because the head loss from pipe resistance is minimal at lower speeds. I currently have a replacement motor on order, Ao Smith Century B2890. This motor line has a more efficient low speed than traditional motors. Price for the motor shipped is $270 and the energy savings should pay for itself within the first year.

[Daox]

That sounds like a good idea. How much electricity will that save you per day?

[pinballlooking]

Last year I got this pump. On lowest setting it uses 65 watts it is 240 volt .
I run it on low power.
I now run it 12 hours a day but it has saved so much power.
Speck Pumps - Badu EcoM3V - Variable Speed
http://usa.speck-pumps.com/pdf/Techn...coM3V_tech.pdf

How many watts does Ao Smith Century B2890 use on low?
That is a good price on that motor.

[oil pan 4]

Just power factor correcting the pump can save up to 30%.
But typical 220v motor setups see about a 5% savings.

[NiHaoMike]

PFC doesn't offer much benefit in residential.

[oil pan 4]

Originally Posted by NiHaoMike

PFC doesn't offer much benefit in residential.

Have you actually tested it?

I have seen new digital power meters with an "80% P.F." kwh counter.
So even if all my tests were wrong, some day we will all get a shinny new kwh meter and surely they will bill more for whats on the "80% P.F." counter.

[gtojohn]

This site has a very good operating cost comparison of various pumps and their operating wattage. It shows monthly costs between $8-$30
It also has some great info on pipe sizing and head loss.
A lot of other factors weigh in with pool pumps but traditionally 1 hp =745 watts. Which can give you an idea of the benefits of proper pump sizing vs oversizing.

[gtojohn]

Energy Efficient Swimming Pools
https://sites.google.com/site/maspooltools/spreadsheets

[Servicetech]

Multispeed PSC motors don't save as much money on "low" and buyign a smaller single speed pump. Currently running a 1/4HP pump on my own pool (uses 250W) for (2) 4hr shifts per day.

[ICanHas]

Originally Posted by Servicetech

Multispeed PSC motors don't save as much money on "low" and buyign a smaller single speed pump. Currently running a 1/4HP pump on my own pool (uses 250W) for (2) 4hr shifts per day.

The motor the thread starter is talking about doesn't change the speed the same way as low/med/hi tapped PSC HVAC fans or shaded pole table top fan motors.

This motor's the real deal true sped with 2 pole/4 pole windings with industrial motor standard rating. A well made AC motor is quite efficient. The motor runs at constant RPM for each setting.

I'm looking in the catalog and I see these specs. You might find them to be strange specs, but fan law will tell you that cutting the fan to 1/2 the speed drops the GPH to 1/2 and (1/2)^3 =1/8 the horsepower requirements, hence 1:8 split.

0.75hp/3450RPM 230v 6.0A@1.67 SF
0.10hp/1725RPM 230v 1.0A @1.67 SF

Those amps are at maximum allowed overload conditions.

I guessed the PF, but I did it so on the conservative side. These motors are heavy and use copper generously, so they're not cheap.

1/6hp @ ~67% (PF at 0.9)
1 1/4 hp @ ~75% (PF at 0.9)
These are plug-to-shaft efficiencies. Not bad for something this size. It's at the 67% overload given in the specs, and they're more efficient when they're not overloaded, so you'll probably get closer to 80% to the shaft.

AC motors are very reliable, tough and they don't create harmonics. Adding a VFD will just make it much more susceptible to surge damage, reduce efficiency and induce high levels of harmonics into the line. You don't need controlled ramp or a bunch of in between speeds for a pool pump. You'll lose another 10% or so of kW going into it in conversion process in the VFD box.

Why the over load rating on motors? It's so you can size it for continuous use at 3/4hp, but have the ability to handle increased load from cleaning attachments and such without the need to actually oversize the motor. It will handle an overload up to 67% for quite some time without issues.

If you run a 3/4 hp VFD with and you overload to 1 1/4 hp load for more than a few seconds, it will let the smoke out.

Attached picture shows you how a common air handler fan is made multi-speed.