Just got slammed with a massive demand charge on our Youngstown facility. Had three 40-ton RTUs kick on simultaneously during a hot July afternoon when the building management system had a glitch. Pulled 420 kW for about 8 minutes straight during FirstEnergy's peak window. Normal peak demand is around 180 kW. Rate schedule GS-3 hit us with demand charges at $14.75/kW so that little episode cost us an extra $3,200 for the month. Anyone else deal with BMS failures causing these nightmare scenarios?
FirstEnergy demand spike from RTU startup - $3200 hit!
Ouch Jim, that's brutal. We had something similar with TVA last summer when our main chiller tripped offline and all the backup units tried to start at once. The inrush current alone set a new peak for 15 minutes. I've started recommending clients install soft-start kits on anything over 20 tons. Costs about $800 per unit but can save thousands in demand charges. Also worth looking into demand limiting controllers that can stage equipment startup.
We see this all the time with Duke Energy customers in Charlotte. The trick is understanding their 15-minute interval windows. If you can spread those startups across two different intervals, you cut the impact in half. I always tell clients to check if their BMS has demand limiting capability built in. Most newer systems do but it's often not enabled by default.
CPS Energy down here uses 15-minute windows too. Had a client with eight rooftop units that would all restart after power outages. Set up a simple sequencing relay that brings them online 30 seconds apart. Cost maybe $200 in parts and labor but saved them from demand spikes every time we get summer storms. Simple fix for a expensive problem.
Connecticut Light & Power just changed their demand window to 5 minutes which makes this even worse. Any HVAC startup event basically guarantees a new peak. We're seeing more clients invest in variable speed drives just to soften the startup curve. The energy savings alone usually justify the cost within two years.
Thanks for the tips everyone. Going to push hard for demand limiting controls on the replacement BMS. The facilities manager is finally convinced after seeing this bill. Also looking into those soft-start kits Terry mentioned. At $14.75/kW, even a small reduction pays for itself quick.
PG&E has been pushing time-of-use rates that make this even more painful. Peak period demand charges can hit $25/kW during summer afternoons. We're seeing more facilities install thermal storage systems to pre-cool before peak hours. Expensive upfront but the demand charge savings are substantial.
Duke Energy actually offers rebates for demand response capable HVAC controls. Might be worth checking if FirstEnergy has similar programs. The utility would rather pay you to avoid the peak than build more generation capacity. Win-win if you can make it work with your operations.