Working with a client in Staunton on Dominion Energy's Schedule GS rate. They're paying $13.25/kW demand charges and the building hits peaks around 180 kW mostly from constant volume air handlers running at full speed. HVAC contractor is recommending variable frequency drives on the major air handlers claiming 20-30% demand reduction. At $8,000 per VFD for six units, that's a big investment. Anyone seen real-world demand savings from VFDs on air handlers? Numbers look good on paper but want to hear actual experience.
Dominion Energy peak shaving - VFDs on air handlers worth it?
We retrofitted VFDs on four air handlers last year here in Huntsville. Alabama Power demand charges are similar at $12.50/kW. Saw about 25% demand reduction during partial load conditions but much less during peak cooling hours when fans run near full speed anyway. The energy savings were more significant than demand savings. Payback was about 4 years total including energy and demand reductions.
Duke Energy territory here in Cincinnati. VFDs definitely help but the savings depend on your control strategy. If you're just doing simple speed control based on temperature, you won't see huge demand benefits. But if you can integrate with a building automation system for demand limiting, the VFDs become much more valuable. We can ramp down fan speeds automatically when approaching peak demand targets.
Eversource here in Connecticut has high demand charges at $18.75/kW. VFDs on air handlers saved us about 15% on peak demand but the bigger benefit was operational flexibility. During demand response events, we can quickly reduce fan speeds across the building without affecting comfort much. Made $2,400 last year just from curtailment payments.
PG&E territory in San Jose. VFDs work best when combined with demand-controlled ventilation. We installed CO2 sensors and occupancy controls so fan speeds adjust based on actual needs rather than just time schedules. Peak demand dropped 22% and energy use fell 35%. At California's high rates, payback was under 3 years.
TVA rates here in Knoxville. One thing to watch with VFDs is power quality. Some older drives create harmonics that can actually increase demand on the electrical system. Make sure you're getting drives with good power factor correction and harmonic filtering. Spent an extra $1,200 per drive for clean power features but avoided power quality issues.
Evergy territory in Kansas City. VFDs are great but don't forget about economizer controls. Free cooling with outside air can eliminate the need to run air handlers at high speeds during mild weather. We combined VFDs with upgraded economizer controls and saw 30% demand reduction during shoulder seasons. Winter and summer peaks didn't improve as much.
Idaho Power rates here. VFDs definitely help but maintenance costs go up. Drives need regular inspection and eventually fail. Budget about $500 per year per drive for maintenance and expect to replace them every 10-15 years. Still worth it for the savings but factor in lifecycle costs when calculating payback.
MLGW here in Memphis. We installed VFDs with demand limiting controllers that communicate with our building automation system. When total building demand approaches our target, the system automatically reduces fan speeds before we hit a new peak. Works great but requires good BAS integration. Can't just bolt on VFDs and expect automatic savings.
Georgia Power territory. VFDs work but consider your building occupancy patterns. If you have consistent full occupancy during peak hours, you won't see much demand reduction because fans still need to run fast for ventilation requirements. Better candidates are buildings with variable occupancy or oversized air handling systems.
Ameren Missouri territory. Don't forget about utility rebates. We got $800 per VFD through Ameren's energy efficiency program. Reduced the upfront cost significantly. Also check if your utility has demand response programs that pay extra for VFD-equipped systems that can respond quickly to curtailment requests.
Duke Energy Charlotte territory. We've installed VFDs on dozens of air handlers over the past few years. Key is proper commissioning. Many contractors install the drives but don't optimize the control sequences. Spend the extra money on good commissioning and you'll see much better performance. Poor commissioning can actually increase energy use.
Thanks for all the feedback everyone. Sounds like VFDs can work but need proper integration with building controls and realistic expectations about demand savings. Going to push for utility rebates and better commissioning in the proposal. At Dominion's rates, even 15% demand reduction would justify the cost over time.
Alice, also consider staging the installation. Start with the largest air handlers that run most consistently and measure actual savings before installing VFDs on every unit. We've seen cases where the first few drives provide most of the benefit and additional units show diminishing returns. Better to prove the concept before committing to the full retrofit.