variable speed pump efficiency

[sktn77a]

OK, so variable speed pumps are more efficient at lower speeds. So which would be the better choice, a 3HP intelliflo VS running at 1000rpm or a 1.5HP superflo VS speed running at a higher speed (2000 rpm?) for the same flow rate.

Or, in accordance with the laws of thermodynamics, would they both use the same energy to pump at the same GPM?

Thanks!

 

[mas985]

Or, in accordance with the laws of thermodynamics, would they both use the same energy to pump at the same GPM?

Exactly!

The only difference is a slight efficiency difference in the drive and the pump design. The Intelliflo has a slight edge but probably not enough to make up the difference in cost over the life of the pump.

For example, at 25 GPM, the difference is about 15 watts.

 

[sktn77a]

OK, thanks. On a related note, how much more efficient would a 1.5 hp permanent magnet SuperFlo VS pump be at 3450rpm, compared to an older 1.0 HP PSC Sta-Rite Dura-Glass single speed pump at the same speed (ie are the permanent magnet pumps significantly more efficient than the PSC pumps at the same speed)?

 

[mas985]

Not all single speed motors are equal. Efficiency ranges from as low as 60% up to as much as 85%. The higher HP motors tend to be more efficient because they use larger gauge wire in the winding's to handle the current. PSC & CSCR motors are bit more efficient than CS only motors. But assuming that pump was a DuraGlas P2RA5E and assuming the same flow rate, the difference is 1690 watts vs 1345 watts or about 20% more efficient.

 

[sktn77a]

Thanks. Very helpful. Just out of curiosity, where do you find all this information?

 

[mas985]

The basis for the information is the Energy Star web site datebase but I use the spreadsheet in my signature to get the values for specific scenarios because the Energy Star data is not set up to compare VS pumps at the same flow rates.