I realize this is kind of off topic, but there are some very bright people on this forum. I have two irrigation pumps a thirty horse and a twenty horse. The demand charges are a killer with P G and E. They are both on a smart meter that will read the highest draw and charge for that. My question is can the amperage draw or demand charge be reduced by using a VFD for a soft start? The demand charges are about 700 a month even if the pump is only run a few minutes. Would change out to an engine, but that is regulated by the Air Resources Board. The thirty horse pump when we are irrigating runs about 3 to 4 thousand a month. Trying to figure out a way to reduce costs. Last month the twenty horse pump was run one day for about eight hours and cost over 400. Most of that was demand charge. Any ideas?
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Using a VFD for a soft start on a thirty horse three phase pump
- Thread starter Nutfarmer
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- Oct 14, 2014
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I use a 30 hp VFD on my 20 horse unit. Big because of one phase input - WAY less than 3 phase charges. A reactor is mandatory for the long run down the well. My motor is 200' down because that is where they hit gravel. Probably should not have put it down to the bottom of the well as static head is 30' and it has never pulled down to 40'.
Still, REA contacted me the first month it ran. Told me my meter must have broke because there was no way I used that much juice. I should have agreed with them.
I can't answer your question about highest draw. Do they hit you for that one second at motor start? A VFD would cure that, but no help for run time unless you could run the motor under 60 Hz.
Still, REA contacted me the first month it ran. Told me my meter must have broke because there was no way I used that much juice. I should have agreed with them.
I can't answer your question about highest draw. Do they hit you for that one second at motor start? A VFD would cure that, but no help for run time unless you could run the motor under 60 Hz.
- Joined
- Jun 12, 2014
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My recollection is the demand charge is the maximum power used over a 15 minute period, not the startup or LR power which is seconds. "The demand charge is calculated using the 15-minute interval in each billing month when your business uses the most electricity. If you can lower your highest usage 15-minute interval, you can save. Your regular electricity usage charges can be roughly 30% lower than for a comparable rate plan without a demand charge.” Not sure if you are metered as residential or a business and there may be a difference in the demand billing. The other question would be does the demand charge change with the TOU, so say if you ran the pumps say the middle of the night would that change the demand charge. Although there are also limits to maximum current drawn/Hp that might also apply. So a soft start would decrease the startup amperage but unlikely to effect the peak demand charge.
Alternative might be a smaller motor run over a longer time frame assuming it can supply enough pressure for the application. If you have 3 phase power in, then and alternative to motor replacement would be to use a 30 Hp VFD and run it at a lower speed, this is the bases of many variable speed pool pumps and you flow is not linear but would need to look at the particular operating curve, GPH and pressure. My only experience is with variable speed pool pumps and at around 70% flow rate I am consuming less than 1/2 motor rated amperage. Fuji makes some reasonably priced 30-40 Hp VFD's of 3 phase input power. There are also high efficiency single phase motors used for pump drives.
Fuji 30 Hp VFD FRN030G1S-2U
Fuji 40 Hp VFD FRN040G1S-2U
Alternative might be a smaller motor run over a longer time frame assuming it can supply enough pressure for the application. If you have 3 phase power in, then and alternative to motor replacement would be to use a 30 Hp VFD and run it at a lower speed, this is the bases of many variable speed pool pumps and you flow is not linear but would need to look at the particular operating curve, GPH and pressure. My only experience is with variable speed pool pumps and at around 70% flow rate I am consuming less than 1/2 motor rated amperage. Fuji makes some reasonably priced 30-40 Hp VFD's of 3 phase input power. There are also high efficiency single phase motors used for pump drives.
Fuji 30 Hp VFD FRN030G1S-2U
Fuji 40 Hp VFD FRN040G1S-2U