Working with a manufacturing facility here in Huntsville on TVA Schedule MSB and they're having issues with HVAC demand spikes every time they lose power. When utility power is restored, their entire HVAC system tries to restart simultaneously creating massive demand spikes. Last month they hit 890 kW during a power restoration event when their normal peak is around 620 kW. That's a 270 kW overage at TVA's $16.43/kW summer demand charge. Looking for solutions to stage equipment restart after power outages.
TVA industrial HVAC - preventing demand spikes during power restoration
Diana power restoration staging is critical for industrial facilities. I recommend time-delay relays on each major HVAC unit set for different intervals - maybe 2, 4, 6, 8 minutes etc. When power comes back, units restart in sequence instead of all at once. Also consider load monitoring relays that prevent restart if building power is already near capacity. At TVA's rates, one bad power restoration can cost $4,400+ annually in demand charges.
TVA territory here in Knoxville and Randy's right about the staging delays. We also use voltage monitoring relays that wait for stable voltage before allowing equipment restart. After power outages, voltage can fluctuate for several minutes as the grid stabilizes. Starting large HVAC equipment during voltage swings can create even higher inrush currents and bigger demand spikes. The voltage monitors add maybe $200 per unit but prevent a lot of problems.
Great suggestions guys. This facility has about 12 major HVAC units so we're looking at staging them over a 25-30 minute period after power restoration. The production manager was worried about comfort issues but I explained that gradually bringing systems online is much better than tripping breakers or creating huge demand spikes. Plus TVA's demand charges last for a full year so one bad restart can cost them all year long. Better to be patient and save money.