Variable Speed pump "sizing" and how do I figure it out

[BigDave]

How do you figure? 2HP @ 1.1 SF vs 2HP @ 1.35 SF?

[kelemvor]

My understanding was that lower sf was better with 1.0 being ideal, am I wrong? e.g 2hp@1.1sf = 1.8hp@1sf or 2hp@1.35 = 1.3hp@1sf

Do I have it backwards?

[BigDave]

As I understand it, Service Factor is an expression of the relationship between design HP and Total HP. Meaning that a 2 HP motor with a Service Factor of 1.1 can (when pressed) deliver 2.2 HP but is designed to run at 2 HP. A 2 HP motor with a SF of 1.35 can (when pressed) deliver 2.7 HP but is designed to run at 2HP. The higher SF motor has more headroom than one that's closer to 1.0 SF. I could be wrong but I'm pretty sure. Either way, the pump curve will be different for different wet-end combinations and when comparing, the pump curves are more important than motor HP.

In your case, I'd bet that the EcoStar would be able to deliver the same spa action as you've seen to date but also allow you to tailor the flow for other operations. As far as comparing the EcoStar to the Intelliflow, I can't help at all. I bought the EcoStar because I can easily integrate it's onboard control system to my Solar heating controller.

[mas985]

All pool pumps are designed to run close to the rated TOTAL HP (label HP * service factor). So a 2 HP motor with a 1.35 SF will run close to 2.7 THP at the best efficiency point of the head curve. Manufactures usually leave a little bit of head room so the motor may never reach the full THP but it will get close. They can do this because a pump on a pool plumbing system has fairly constant load and torque requirements do not vary much.

Also, most pump lines come in an up rated vs full rated version. So an up rated 2 HP pump (1.23 SF), will have exactly the same performance as a 1.5 HP (1.65 SF) full rated pump in the same pump line. It is simply a relabeling of the motor but the wet ends have identical parts and so the head curves are identical.

So when comparing motors and/or pumps, you need to compare the THP, not just the label HP and not just the SF but both combined. But even that does give you a good representation of the pump. The head curve is a much better indicator of the power of the pump.

[kelemvor]

I guess that's why hayward publishes only the head curve in their documentation and withholds information about horsepower and service factor entirely. Thanks for the lesson!

[mas985]

If you look as some of the manuals and brochures, Hayward lists the label HP and service factor. For example:

http://www.hayward-pool.com/pdf/lite...RateSS11_5.pdf

[kelemvor]

I forgot that I'd emailed hayward and asked about the motor last week. Daly from Hayward Technical Services just got back to me today with:

The EcoStar pump has a Rated HP of 2.7, SF of 1.00 and a Total Rated HP of 2.7.

Although given what BigDave's label says I would guess this guy is wrong.. or maybe they switched motors.