Demand Control Ventilation is a control system that varies the volume of exhaust (and supply) based on cooking activity. Since there are idle and peak periods for most cooking operations, the potential to save fan and HVAC energy is significant. ASHRAE 90.1 (American Society of Heating Refrigeration and Air Conditioning Engineers) establishes design standards for building ventilation. 90.1 is for commercial spaces. Within in the standard it defines the requirement that for kitchens exhausting in excess of 5000 cfm of exhaust. You must deploy one of three energy saving strategies, Heat recovery, 50% transfer air or demand control ventilation on the kitchen exhaust. This is also a prerequisite for LEED certification. If the project or facility is not bound by those requirements, then it’s an economic question of whether the investment necessary to deploy a Demand Control Ventilation system pays back in energy savings in sufficient time to be acceptable for the project.