According to APSP Pump Database Web Site, these are some of the numbers for Intelliflo VS and WhisperFlo dual speed 2HP.
Intelliflo at 1100 RPM: 24 GPM, 145 W
WhisperFlo at 1725 RPM: 37 GPM, 395 W
I assume these measurements are tested under similar conditions (ie. TDH). So I can assume a similar saving ratio at anyone's house.
At $0.12 /KWh, the annual cost to run these two pumps to turn over a 22500 G pool as follows:
Intelliflo: 22500 / (24*60) = 15.625 hours per turnover.
145 W * 15.625 = 2.27 kWH / day
2.27 * 365 * $0.12 = $99 / year
WhisperFlo: 22500 / (37*60) = 10.135 hours per turnover.
395 W * 10.135 = 4.00 kWH / day
4.00 * 365 * $0.12 = $175 / year
At these settings, I will save $76 / year to run an IntelliFlo vs WhisperFlo dual speed. The price difference between the two pumps is $200. So it takes about 3 years to break even. However, quite a few users said that it is unlikey to break even when the utility rate is under $0.15 / kWH. Am I missing something here?