Variable Speed Pumps

[Extreme21]

I want to upgrade my Sta-Rite Max-E-Glas II pump to a more energy efficient variable speed pump. My pool is 19x23 13,500 gallon pool that is 5ft in the deepest section with no spa attached, and I want to make sure that I am not going to purchase a pump that is overkill for my size pool. I am averaging 28 kWh a day at an average cost of .22 and hour. I originally was going to purchase the Pentair Intelliflo VS, the saw that Hayward has the Max-Flo VS which is less horsepower and $$, and explains that it will save the same amount of money as the Pentair. Does anyone have any info that would help me decide. Attached are photos of my pool equipment setup.IMG_1167.jpgIMG_1173.jpgIMG_1170.jpg

[mas985]

The Max-Flo VS is a lower head pump and it is actually more "efficient" (higher energy factor) than some of the bigger pumps. So it is a pretty good choice at a great price point. The only downside to it is that it would not work well for a pool with a spa where the VS would need to run the jets too. But everything else would work fine.

Here is a spreadsheet comparison I did some time ago for $0.20/kwh which is close to yours.

[PoolDoc]

Thanks for that very helpful response, Mark.

[PoolDoc]

One question -- how did you determine motor efficiency?

[mas985]

The efficiency comes from the CEC/APSP database but I am not using it in any of the calculations. It is information only. I believe it represents the full load motor efficiency so it really isn't relevant for a specific operating point. Also, it doesn't really have a correlation to which pump has the better operating cost either.

[PoolDoc]

Do you know if whether V*A gives a close approximation to watts, or whether the power factor is large enough (or small enough) to make that inaccurate?

[Extreme21]

Mark,

Thank you for the response. The chart is very helpful.

Matt

[mas985]

Do you know if whether V*A gives a close approximation to watts, or whether the power factor is large enough (or small enough) to make that inaccurate?

V*A is certainly an upper limit because it assumes a PF of 1 but over a pump's head curve, the motor load can vary from around 40% to 100% and the power factor is dependent on load. At peak load the PF is usually not better than 0.9 but I haven't measured it directly on a pump. The following paper shows some of the effects but in general, I don't think you can count on the PF being close to 1 for an induction motor. There is always a reactive part to the power.

http://www1.eere.energy.gov/manufact...s/10097517.pdf

The best way to measure pump power is by using the power company meter on the side of the house. You can get a measurement with the pump vs off and get a much better estimate as long as nothing else changes in the house between measurements. I have a digital meter and it is pretty easy to get the power difference but you can do the same with the old style analog meters too.