Real World results from installing a VFD on a three phase pool motor. This is not about a prepackaged pools store system.
I want to preface this text by explaining that I am a DIY’er.
My single phase 1.5 hp 240-volt motor died recently. It was used to drive a 1.5 hp challenger pump. I live in rural Midwest setting so I run the pump from mid-May until mid-September at closing. With the dust and debris blowing around it just works best; I rather pay extra electricity than spending the same amount of money on chlorine to shock.
This year I replaced the motor (old one died) with a three phase 1.5 hp 240-volt motor. I also purchased a 3 hp VFD that is single phase 240 V input with three phase 230 V output. This VFD has a dial to ramp the hertz from 0 to 60 cycles.
Here are my results.
Costs of motors are a wash. The three phase was dollars cheaper than comparable single phase.
Cost of 3 hp VFD (had to de-rate due to the 240 single phase input) was $230 delivered. If I would have had single phase 120-volt I would not have had to de-rate for a few of the different VFD’s out there which would have saved me
$20 – $40.
Electrical costs for my Rural Electrical Coop are $0.16/kwh from 4 pm to 9 pm and $0.083/kwh from 9 pm to 4 pm. Here is where the fun starts.
At 60 hertz I am pulling 5.9 amps at 244 V, that equals = 1140 watts (5.9 * 244 ).
So, 1.140 kw * 5 hours/day = 7.2 kwh
7.2 kwh * $0.16/kwh = $1.15 for peak charge hours/day
So, 1.140 kw * 19 hours/day = 27.4 kwh
27.4 kwh * $0.083/kwh = $2.27 for off peak hours/day
Total at 60 Hz = $3.42/day
Now at 30 hertz the electrical saving is realized. I am pulling 1.2 amps at 244 V , that equals 293 watts (1.2 * 244)
So, 0.293 kw * 5 hours/day = 1.47 kwh
1.47 kwh * $0.16/kwh = $0.24
So, 0.293 kw * 19 hours/day = 5.57 kwh
5.57 kwh * $0.083/kwh = $0.46
Total at 30 Hz = $0.70/day
Let’s assume that the watt draw for the single phase and three phase are equal in this next text part.
Thanks, to the pump affinity law we know at half speed of pump is half flow. Using this logic running a single-phase motor for 12 hours/day off peak would cost 1.140 kw times 12 hours = 13.68 kwh.
13.68 kwh * $0.083 = $1.14/day.
The same flow rate would be achieved by running the three-phase motor at 30 Hz for 24 hours/day.
0.293 kw * 24 hours = 7.03 kwh
7.03 kwh * $0.083/kwh = $0.58/day
Difference of $1.14 - $0.58 = $0.56/day.
For those of you that would want to do this, you would spend around a total of $250 on a VFD, enclosure, and incidentals, the ROI is 446 pools days. Here in the Midwest that is 5 years. Again this is based on my electrical costs, and my size of pump. This will vary greatly where you live. Obvious is higher electrical cost would make one want to do this. Also down south or on the coasts where the seasons are long one would want to do this.
Now if you are like me, I ran my single phase pump 24/7, my ROI for my VFD is 2 pool seasons. This is due to the run time going through the peak hours.
I am not sure why this idea has not caught on this website since it is clearly a good ROI. The flexibility of a VFD not only saves money, lowers pump noise and also the ability to simply crank up the speed during vacuuming or after a storm is great. The salt water guys should all be doing this since they must keep the water flowing.
I want to preface this text by explaining that I am a DIY’er.
My single phase 1.5 hp 240-volt motor died recently. It was used to drive a 1.5 hp challenger pump. I live in rural Midwest setting so I run the pump from mid-May until mid-September at closing. With the dust and debris blowing around it just works best; I rather pay extra electricity than spending the same amount of money on chlorine to shock.
This year I replaced the motor (old one died) with a three phase 1.5 hp 240-volt motor. I also purchased a 3 hp VFD that is single phase 240 V input with three phase 230 V output. This VFD has a dial to ramp the hertz from 0 to 60 cycles.
Here are my results.
Costs of motors are a wash. The three phase was dollars cheaper than comparable single phase.
Cost of 3 hp VFD (had to de-rate due to the 240 single phase input) was $230 delivered. If I would have had single phase 120-volt I would not have had to de-rate for a few of the different VFD’s out there which would have saved me
$20 – $40.
Electrical costs for my Rural Electrical Coop are $0.16/kwh from 4 pm to 9 pm and $0.083/kwh from 9 pm to 4 pm. Here is where the fun starts.
At 60 hertz I am pulling 5.9 amps at 244 V, that equals = 1140 watts (5.9 * 244 ).
So, 1.140 kw * 5 hours/day = 7.2 kwh
7.2 kwh * $0.16/kwh = $1.15 for peak charge hours/day
So, 1.140 kw * 19 hours/day = 27.4 kwh
27.4 kwh * $0.083/kwh = $2.27 for off peak hours/day
Total at 60 Hz = $3.42/day
Now at 30 hertz the electrical saving is realized. I am pulling 1.2 amps at 244 V , that equals 293 watts (1.2 * 244)
So, 0.293 kw * 5 hours/day = 1.47 kwh
1.47 kwh * $0.16/kwh = $0.24
So, 0.293 kw * 19 hours/day = 5.57 kwh
5.57 kwh * $0.083/kwh = $0.46
Total at 30 Hz = $0.70/day
Let’s assume that the watt draw for the single phase and three phase are equal in this next text part.
Thanks, to the pump affinity law we know at half speed of pump is half flow. Using this logic running a single-phase motor for 12 hours/day off peak would cost 1.140 kw times 12 hours = 13.68 kwh.
13.68 kwh * $0.083 = $1.14/day.
The same flow rate would be achieved by running the three-phase motor at 30 Hz for 24 hours/day.
0.293 kw * 24 hours = 7.03 kwh
7.03 kwh * $0.083/kwh = $0.58/day
Difference of $1.14 - $0.58 = $0.56/day.
For those of you that would want to do this, you would spend around a total of $250 on a VFD, enclosure, and incidentals, the ROI is 446 pools days. Here in the Midwest that is 5 years. Again this is based on my electrical costs, and my size of pump. This will vary greatly where you live. Obvious is higher electrical cost would make one want to do this. Also down south or on the coasts where the seasons are long one would want to do this.
Now if you are like me, I ran my single phase pump 24/7, my ROI for my VFD is 2 pool seasons. This is due to the run time going through the peak hours.
I am not sure why this idea has not caught on this website since it is clearly a good ROI. The flexibility of a VFD not only saves money, lowers pump noise and also the ability to simply crank up the speed during vacuuming or after a storm is great. The salt water guys should all be doing this since they must keep the water flowing.
