Working with a large office building here in Knoxville on TVA's Schedule GSA and we've implemented some solid demand limiting strategies for their HVAC system. They were consistently hitting 450-480 kW peaks during summer afternoons when all zones were calling for cooling simultaneously. We installed a demand controller that stages compressor operation and limits total HVAC load to 350 kW maximum. The building stays comfortable and they're saving about $1,800/month at $13.85/kW demand charge. What strategies are working for you guys?
TVA Schedule GSA - HVAC demand limiting strategies that actually work
Wisconsin Public Service up here in Green Bay and we use thermal mass strategies. Pre-cool buildings during off-peak hours and coast through the peak demand periods. Works great for office buildings and retail spaces with good insulation. Saved one client 65 kW during their afternoon peak by shifting cooling load to early morning hours. The key is having good zone control and understanding your building's thermal characteristics.
LG&E here in Louisville and ice storage systems work well if you have the space and budget. Client installed a 200-ton ice system that makes ice overnight during low demand periods. During peak hours from 1-6 PM, they use stored ice for cooling and barely run the chillers. Cut their summer peak demand by 180 kW. The payback was about 6 years but LG&E also gave them rebates that shortened it to 4 years.
Ice storage is nice Pete but expensive upfront. We're seeing good results with variable speed drives on larger equipment. Older constant-speed units cycle on/off creating demand spikes but VSD units can ramp up gradually. Installed VSD retrofits on four 40-ton units and eliminated the startup surge completely. Also allows for better load management during peak periods - you can throttle back cooling slightly without losing comfort.
Avista up here in Spokane and building automation integration is key. Our demand controller talks to the BAS and can shed non-critical HVAC zones when approaching the demand limit. Things like storage rooms, mechanical spaces, and unoccupied areas get temporarily reduced cooling. Most occupants never notice but it can save 40-50 kW during peak periods. The BAS automatically restores full cooling once the peak period passes.
Larry that's smart load shedding. We also use economizer controls heavily up here. When outside air is cool enough, we can provide "free cooling" and reduce chiller load significantly. Even saved 30 kW on a 75-degree day last month by using outside air instead of mechanical cooling in the early morning hours. The key is having good damper controls and enthalpy sensors.
Duke Energy here in Charlotte and we're seeing excellent results with thermal storage using the building structure itself. Concrete floors and walls can store significant cooling overnight. Run chillers hard from midnight to 6 AM when demand charges are lower, then coast on stored cooling during peak hours. One client reduced their peak demand by 85 kW just by adjusting their scheduling and using building mass as a battery. Sometimes the old methods work best.