Replacing pump motor

[mas985]

AO Smith, now owned by Regal Beloit, is the primary OEM motor supplier for most residential pool pumps so they would be a good replacement. They have recently come out with a high efficiency two speed motor which uses a run capacitor on low speed as well as high speed. They are claiming a 20% improvement on low speed with this new motor. Unfortunately, it only comes in a 56y frame at this point.

You can find more information here:

http://www.aosmithmotors.com/WorkAre...mID=2147483754

[PoolDoc]

Mark, I've been doing some work with the Calif state ratings, and have been surprised at some of the efficiency figures. I looked, but could not find, any data on AO Smith's motor efficiency. Have you seen any data on that?

[mas985]

No but I talked with a rep and he said that AO Smith does not publish their efficiency data directly but he did say that the numbers in the CEC database are probably correct. He also confirmed the 20% improvement noted in the brochure. Theoretically, a low speed 20% efficiency improvement is predictable with the addition of a run capacitor. A typical two speed motor does not use a run capacitor on low speed so the efficiency of the motor is about half of that on high speed. Because the motor is significantly underloaded due to the speed change, the power factor is quite low so there is quite a bit of I^2R losses in the motor. The run capacitor shifts the current more in line with the voltage so the power factor increases and total current decrease improving the efficiency of the motor. But again, this efficiency improvement is only on low speed.

[PoolDoc]

Interesting. If I'm understanding what I'm reading in the California data, that would me the new 2speed motor significantly more efficient on low speed than the VFD motors. I was amazed to see that some of them are reported run as low as 33% efficiency!

[mas985]

Yes, the efficiency on low speed is quite low. Besides the power factor, the main reason for low efficiency is the secondary winding is much thinner (higher gauge) wire than than the primary winding so it has very high resistance. That is the only way they can make a dual winding motor with the same diameter as the single speeds. Improving the power factor helps but improving 45% efficiency by 20% is still only 54% efficiency and that is not better than a VS at any speed.

A VS can maintain high efficiency down to the lowest speeds because it changes the line frequency and voltage plus it always uses the same winding. One thing to note is the Intelliflo shows a higher efficiency at all speeds while the EcoStar shows a significant decrease in motor efficiency (33%) but that can't really be true because the EcoStar has a much better energy factor at 1000 RPM speed than the Intelliflo. Plus the wire to water efficiency of the EcoStar is 35% (Curve-C) at 1000 RPM which cannot be higher than the motor efficiency so there is clearly an issue with some of the data. Other issues with the data include the Whisperflo where the Whisperflo full rate and up rated version of the same THP pump should be identical and in some cases they are way off. However, from my own observations, most of the data seems to be pretty reasonable but there some glaring errors.

[bbsmith]

Thanks for all the input.

But after reading thru everything I am a little confused?

Which type of motor is more energy efficient (uses less KW or Amps to run a pool, Cost less)
VFD or ectro-mechanical hi-E 2-speed?

And does the ImPower have the same efficent as a VFD? The specs say that the ImPower has max 1.25 Output (1 HP up-rate) and 3 speeds (3450, 2600, 1725)

[PoolDoc]

ImPower appears to be a VFD with preset, rather than variable, speeds. It also has a pretty inflexible -- and unchangeable -- control program.

Mark (mas985) has looked at motor efficiency more than I. But from what I can tell:
+ companies (including AOSmith) haven't published motor efficiency figures for fractional (under 5HP) motors.
+ the California data, which shows OVERALL efficiency of pumps, in some cases compares identical wet ends mated with either dual speed or VFD motors. This data contains some obvious errors. BUT, it looks like the VFD motors may be a little more efficient. However, the difference probably will NOT be large enough for you to notice on your power bill.

[mas985]

Which type of motor is more energy efficient (uses less KW or Amps to run a pool, Cost less)
VFD or ectro-mechanical hi-E 2-speed?

A VS will always be more efficient and cost less to run but it may not be enough to pay for the extra cost of the pump.

And does the ImPower have the same efficient as a VFD? The specs say that the ImPower has max 1.25 Output (1 HP up-rate) and 3 speeds (3450, 2600, 1725)

The ImPower would probably be more efficient than the same size two speed motor but not as efficient as a true VS. A VS has the ability to optimize the speed for the particular job, where as the IMPower is a fixed three speed, so there is less flexibility.

The cost savings for any of these options will depend on how the pump is used. With solar, you will be using the pumps at high(er) speed most of the time so may see only a small change in your power bill. However, the VS would allow you to set the speed for just enough flow rate to keep the vacuum release closed and minimize energy use.