Sam from Atlanta. Client added a 75 hp air compressor to his manufacturing line three months ago. His demand charges have roughly tripled. He did not consult me before the installation and is now asking why his bills are so high. The compressor starts cold every morning and draws enormous inrush current. Is there anything recoverable here or is this just the new reality?
Client installed a large air compressor and demand charges tripled
Derek from Charlotte. The inrush problem is real. A 75 hp motor starting across the line can draw 6 to 7 times its running current for the first few seconds, which registers as a demand spike. Whether that spike is recoverable depends on the utility's meter interval and whether the spike duration falls fully within a 15-minute window.
Derek, the compressor start takes about 45 seconds from cold. That spike would be fully within the 15-minute demand window.
Derek again. Correct, so the spike is contributing to the demand reading. Going forward the fix is a soft starter or variable frequency drive on the compressor motor. Reduces the inrush significantly and can drop the demand contribution by 30 to 40 percent. That is a capital improvement conversation, not an audit dispute.
Helen from Phoenix. Sam, also pull the interval data and find exactly which 15-minute window the peak is occurring. If it is always at the same time every morning that confirms the compressor start. Some utilities have demand interval averaging provisions for known motor starts — worth checking the tariff.
Helen I did not know tariff provisions for motor starts existed. What would I search for?
Helen again. Search the tariff for motor starting, inrush current, and demand averaging. Some schedules have language that excludes or averages brief motor starting currents from the billing demand. Rare but worth checking in older industrial tariffs.