Office building in Knoxville, TVA-served through Lenoir City Utilities. Building has 4 elevators in a 12-story tower. Building engineer claims elevator motor starting is creating demand spikes. Looking at interval data I can see brief spikes of 40-60 kW above baseline that coincide with elevator peak usage times. But TVA uses 30-minute demand intervals. Can a few seconds of motor inrush during each elevator start actually affect a 30-minute average?
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Elevator motor starting transients ? are they really hitting demand?
Vernon ? thats an important distinction. So its not the starting transient but the sustained running load when multiple elevators operate simultaneously. The building has 4 elevators at 30 HP each. If all four run simultaneously thats roughly 90 kW of sustained motor load on top of everything else.
Edward ? in Hartford I audited a 20-story building with 6 elevators on Eversource 15-minute intervals. The elevator dispatch system was programmed to run all cars during peak hours. Reprogramming to limit simultaneous car operation to 4 of 6 during peak demand periods reduced building demand by 45 kW. Two cars parked during the peak 15-minute window. Minimal impact on wait times, measurable impact on demand.
Alice ? limiting elevator car dispatch is a clever demand reduction strategy for tall buildings. But the property manager needs to be comfortable that tenant satisfaction wont suffer. In a 20-story building reducing from 6 to 4 active cars during a 15-minute window probably adds 15-20 seconds to average wait time. Thats acceptable. In a busy hospital that could be a problem.
Good discussion. The building manager is willing to park 1 of 4 elevators during the peak demand window ? they already park one overnight. Extending that parking period to cover the noon-1pm demand peak would reduce simultaneous elevator load. Estimating 22 kW demand reduction at $8.50 per kW thats $187 monthly or $2,244 annually. Small but zero cost to implement.
Implemented the elevator parking strategy. After 3 months of data the actual demand reduction averaged 18 kW ? slightly less than projected because some peak intervals occurred outside the elevator parking window. Annual savings approximately $1,836. Not a headline finding but when combined with other demand reduction measures across the building it contributes to the overall package.
Edward ? elevator inrush current lasts 2-5 seconds per start. With a 30-minute demand interval thats negligible. A 60 kW inrush for 5 seconds averaged over 30 minutes adds less than 0.2 kW to the interval demand. The spikes youre seeing in interval data are NOT elevator inrush ? theyre sustained elevator motor run time during peak traffic. Multiple elevators running simultaneously for extended periods during lunch hour or end of day can add 80-120 kW of sustained demand.