Client in Knoxville got hit with a massive demand spike last month when their new 60-ton rooftop unit kicked on during peak hours. TVA Schedule GSA-2 demand went from 150kW baseline to 387kW for just 15 minutes. That single spike cost them $3,200 in demand charges for the entire billing period. The unit has soft-start capability but it wasn't properly configured by the installer. Anyone else seen HVAC contractors skip the soft-start programming? This is becoming a real problem with new high-efficiency units.
TVA demand spike after HVAC compressor startup - $3,200 surprise
Seen this exact issue with PSO customers in Tulsa. New Carrier units with variable speed drives that aren't commissioned properly. The inrush current on startup can be 6-8 times normal operating amperage. For a 50-ton unit that's normally drawing 60kW, you're looking at 350-450kW on startup. Most contractors don't understand demand billing - they just care if the unit cools the building.
FirstEnergy territory here in Youngstown - same story different day. Schedule GP demand rates are killing these customers. What really gets me is when multiple units cycle on simultaneously due to poor sequencing. Had a warehouse customer hit 892kW peak when three 40-ton units started within 30 seconds of each other. Normal demand was around 200kW. The demand charge alone was $8,400 that month.
APS here in Phoenix - we see this constantly during summer months. The key is staging the startups and using demand limiting controls. I always recommend customers invest in a basic demand controller that can delay HVAC starts when approaching their historical peak. Simple $2,000 device can save $20,000+ annually in demand charges. The payback is usually under 3 months during cooling season.
Ameren Missouri customers face similar issues. Schedule LGS demand charges are $18.50/kW in summer. Terry, did your client consider adding a soft-start kit after the fact? We've had good luck with aftermarket solutions from companies like NatGen. Usually runs $3,000-5,000 installed but pays for itself immediately if you're seeing those kind of demand spikes.
Pam - yes, we ended up retrofitting a MicroAir soft-start on the problem unit. Installation was straightforward and the next month's demand dropped back to normal levels. The customer is thrilled. What frustrates me is that the original contractor charged $85,000 for the new unit and skipped a $1,200 option that would have prevented the problem entirely. Now the customer doesn't trust HVAC contractors and calls me before any major equipment decisions.
Duke Energy Ohio here in Cincinnati - we're seeing more awareness from contractors lately but still plenty of issues. I always tell customers to specify soft-start in the HVAC contract and require commissioning documentation. The newer Trane and Carrier units have great built-in demand limiting features but only if they're properly programmed during startup.
Great thread Terry. In Kentucky with LG&E, I've started recommending customers hire a commissioning agent for any HVAC project over $50k. Costs about $2,000-3,000 but ensures everything is configured correctly from day one. Too many expensive lessons learned the hard way with demand charges. The commissioning report also gives you documentation if there are problems later.