there are some 1-speed vs 2-speed thread with excellent info, however this thread is for the expert to check my math.
* pool is 30,000 gallon. filtration target is a 1 turnover per day. vacumm target is 2 hour per day. *
pump is a hayward super pump. with a 2HP motor and with a 40' head. yield is 98gpm.
south florida electricity is $0.11 per kilowatt/hr.
note: there are obviously other factors that comes into play. however since this is on the same pool, same plumbing, same everything except motor. all those factors should negate each other.
recently bought a 1-speed motor (from the local pool shop) about 2 weeks ago (never heard of 2-speed or variable-speed. yep first pool).
1-speed motor on hand is century centurion pro ST225. 3450rpm. 230v @ 10.2amp. 2346watt.
cost $0.26 per hour pumping 5880 gallon.
2-speed motor in consideration is a century 2-speed B2979. 3450rpm/1725rpm. 230v @ 11.0amp/1.6amp. 2530watt/368watt.
full speed - cost $0.28 per hour pumping 5880 gallon
low speed - cost $0.04 per hour pumping 2940 gallon.
THE MATH (this is what need to be checked)
1-speed motor to push 30,000 gallon. 5880 gallon per hour. takes 5.1 hour. costing $1.32. both filtration and vac requirements met.
2-speed motor to push 30,000 gallon. 11760 gallon first two hour for vac. costing $0.56. 18240 gallon remaining needs filteration. motor need to run for additional 6.20 hours. costing $0.25.
a saving of $0.51 per day.
not convince that this motor (B2979) is capable of running 1725rpm @ 1.6amp (15% of full speed amperage draw).
it's predeccessor B979 required 4.1amp at low speed. let use 4.1amp correction for the low speed draw.
11760 gallon first two hour for vac. costing $0.56. 18240 gallon remaining. motor need to run for additional 6.20 hours. costing $0.64.
an adjusted saving of $0.12 per day.
online shipped: 1-speed is $225 (ao smith) vs 2-speed is $317 (century). difference of $92.
savings of $0.51 per day. going to take 6 months to break even.
adjusted savings of $0.12 per day. going to take 26+ months to break even.