Nashville client asked about installing a demand limit controller. The sales rep from the controller company promises 15-20% demand reduction by automatically shedding non-critical loads when demand approaches a setpoint. Cost is $18,000 installed. Sounds too good to be true for a 400 kW commercial building. Has anyone had clients install these and seen real results?
Demand limit controllers ? do they actually save money?
James ? demand controllers work but the savings depend entirely on how much sheddable load the building has. A building where 30% of the load is deferrable ? water heaters, non-critical HVAC, pool pumps, EV chargers ? can see real demand reduction. A building where 90% of the load is non-negotiable ? production equipment, data center, hospital ? gets minimal benefit. The controller can only shed what the building can afford to shed.
David ? this is a mixed-use commercial building. Retail on the ground floor, offices above, mechanical penthouse with chillers. The sheddable loads would be chiller staging, non-essential lighting, and office HVAC setpoint adjustments. Maybe 120 kW of sheddable load out of 400 kW total. So realistically 30% demand reduction potential.
From the engineering side ? demand controllers are most effective when combined with thermal storage. Pre-cool the building before peak demand periods, then shed HVAC during the peak interval while the building coasts on stored cooling. Without thermal mass to coast on, shedding HVAC during a Tennessee summer afternoon means the building temperature rises quickly and tenants complain within 15-30 minutes.
Had a client in Birmingham install a demand controller on a 600 kW manufacturing facility. Alabama Power Rate FPL. The controller shed compressor cycling loads and warehouse ventilation fans when demand exceeded 520 kW. First year savings were $11,400 ? about 12% demand reduction. The $22,000 controller paid for itself in 23 months. But the maintenance staff hated it because the load shedding caused temperature fluctuations in the warehouse that affected product quality.
Terrence raises the operational impact issue. In Hartford I had a client unplug their demand controller after 6 months because the automatic load shedding was disrupting business operations. The controller saved demand charges but created operational costs that werent in the ROI calculation. Tenant complaints, product quality issues, employee comfort ? these have real costs too.
Virginia makes a critical point. The ROI calculation from the controller salesperson never includes operational disruption costs. Ill recommend my Nashville client do a 30-day manual demand management test before committing $18,000 to automation. If they can manually shed loads during peak intervals without complaints, the controller makes sense. If manual shedding causes problems, automation wont solve that.
Reporting back ? client did the 30-day manual test. Manually shed chiller staging and non-essential lighting during peak intervals. Demand dropped 85 kW. No tenant complaints. They decided to invest in the controller to automate what they successfully tested manually. Projected annual savings of $9,600 against $18,000 installed cost. 22-month payback with minimal operational risk because they validated the strategy first.