Pete here from San Jose. Working with a client on PG&E's A-10 TOU rate and they're getting killed on summer demand charges. They have three 75-ton chillers that all start up around 8 AM when the building opens. Current demand peak is hitting 890 kW, costing them about $18,500/month just in demand charges during summer months. Considering retrofitting with VFDs and sequencing controls. Anyone have real-world data on how much VFDs actually reduce startup demand spikes?
PG&E A-10 rate: VFDs on chillers worth it for demand reduction?
Greg here from Atlanta. Just finished a similar project with Georgia Power. Three 100-ton chillers with VFDs reduced startup demand by about 65%. Instead of all three hitting full load in 2-3 minutes, the VFDs ramp them up over 8-10 minutes. Dropped peak demand from 1,200 kW to about 750 kW. Demand charge savings alone paid for the VFDs in 14 months. Make sure you get proper sequencing controls too - that's half the battle.
Chuck from Cincinnati here. We did VFDs on four 60-ton units for a Duke Energy customer last year. The demand reduction was significant but here's what nobody tells you - you need to watch your power factor. VFDs can hurt your power factor if not properly configured, and Duke has penalties for anything under 0.9. We had to add power factor correction capacitors. Still worth it overall but factor that into your cost analysis.
Derek H. in Atlanta. One thing to consider with PG&E A-10 is the time-of-use periods. Summer peak is 2-9 PM now, so morning startup spikes might not hit your peak demand window anyway. But if those chillers are cycling during afternoon peak hours, that's where VFDs really pay off. I'd run an analysis of when your actual demand peaks occur throughout the day before making the investment.
Susan from OKC here. Working with OG&E commercial rates. VFDs definitely help but don't overlook economizers and free cooling strategies. If you can delay chiller startup by an hour or two with outside air cooling, that often has bigger demand impact than VFDs alone. Especially in California where you have good temperature swings. Combined approach usually works best.
Juan from New Orleans. Entergy has similar rate structures. VFDs are great but make sure your controls contractor understands utility rates. Had one job where they programmed the VFDs to ramp up too fast during peak hours because they didn't understand the 15-minute demand window. Ended up with higher demand charges than before! Controls programming is just as important as the VFDs themselves.
Good points everyone. I'm definitely leaning toward the VFD retrofit now. The client's peak demand is actually hitting during the 2-9 PM period when the afternoon heat builds up, so it should make a real difference. Going to spec proper sequencing controls and power factor correction from the start. Will report back with actual results in a few months.
Bobby here from Memphis. Just want to add that MLGW recently changed their demand window calculation method. They now use a rolling 15-minute average instead of fixed intervals. Makes VFDs even more valuable because you can't just time your startups to specific windows anymore. The gradual ramp-up is really the only way to control demand now.
Bobby makes a great point. More utilities are moving to rolling averages. Georgia Power switched last year too. The old tricks of timing startups don't work as well anymore. VFDs with smart sequencing are becoming essential for any multi-chiller facility. The technology has really matured in the last few years too - much more reliable than the early VFD systems.
Tim from Bismarck here. Great discussion. One more consideration - make sure your maintenance staff understands the new system. Had a client where maintenance bypassed the sequencing controls during a 'routine cleaning' and forgot to turn them back on. Next month's bill was $12,000 higher because all three chillers started simultaneously during peak hours. Training is just as important as the technology.
Jim from Minneapolis weighing in. Xcel Energy has been pushing VFDs hard through their rebate programs. Just finished an analysis showing average demand reduction of 58% on chiller startups with properly configured VFDs and sequencing. The key is working with a controls contractor who really understands both the HVAC side and the utility rate implications. Worth every penny when done right.