Had a client get nailed with an $8,400 demand charge spike last month on their Duke Energy bill here in Charlotte. They run a 40,000 sq ft office building and their HVAC system creates a massive draw when it starts up after weekend setbacks. The demand meter caught a 487 kW peak during Monday morning startup - their normal operating demand is around 280 kW. Anyone else seeing Duke getting more aggressive about capturing these startup spikes? I'm thinking we need to look at soft-start equipment or staging the units differently.
Duke Energy hit us with $8,400 demand spike - HVAC startup sequence
Derek, we see this constantly with TVA customers here in Knoxville. The key is understanding Duke's demand measurement - are they using 15-minute windows or instantaneous peaks? Most commercial buildings can reduce startup demand by 30-40% just by sequencing their rooftop units with 2-3 minute delays between each start. Simple timer relay modifications can save thousands. What's their current startup sequence look like?
This is exactly why I always recommend VFDs on larger HVAC systems here in San Antonio. CPS Energy uses 15-minute demand windows and those startup spikes will kill you in the summer. Had a manufacturing client drop their demand charges by $12,000/year just by installing soft-starts on their 150-ton chillers. The payback was under 18 months. Derek, what's the building's load profile look like during normal operations?
Similar issue with Dominion Virginia Power customers. The problem gets worse when you have multiple large units trying to start simultaneously after a power outage or extended shutdown. I've had good luck with demand controllers that can shed non-critical loads during HVAC startup. Also check if Duke offers any demand response programs that might offset some of these charges. Some utilities will pay you to allow them to cycle your equipment during peak periods.
Terry and Angela - great points. Duke is using 15-minute intervals but they're catching the inrush current on the compressor starts. The building has 6 rooftop units, 15-20 tons each, and they all kick on within about 30 seconds of each other Monday mornings. Building automation system isn't very sophisticated. Phil, what kind of demand controller would you recommend? Budget's probably around $15-20K for a solution.
Derek, for that budget you could get a really nice Schneider or Honeywell demand controller with HVAC integration. The key is setting it up to stage your rooftop units with 3-5 minute delays between starts. You might also want to look at soft-start kits for the compressors - probably $800-1200 per unit but they'll cut that inrush current in half. Here in Hartford with Eversource, we've seen similar savings. What's their current demand charge rate structure?
Don't forget about power factor correction either. HVAC motors starting up can create terrible power factor issues which some utilities penalize. PECO here in Philly charges extra for poor power factor. Adding capacitor banks or upgrading to high-efficiency motors with better power factor can help. Also, check if the building has any energy storage options - even a small battery system could help smooth out those demand spikes.
One more thing to consider - preventive maintenance on those HVAC units. Dirty coils, low refrigerant, or worn compressors will draw more power during startup. We had a client in Sacramento where SMUD was hitting them hard on demand charges until we discovered two of their units had refrigerant leaks causing the compressors to work harder. Simple maintenance fix saved them $300/month in demand charges.
All great advice here. Derek, one quick win might be adjusting the building setback temperatures. Instead of letting it get too hot/cold over weekends, keep it closer to occupied setpoints. The HVAC won't have to work as hard Monday morning. We do this a lot with NES customers in Nashville. Yeah, you'll use a bit more energy over the weekend, but avoiding that demand spike usually makes it worthwhile. What are their current setback settings?