An HVAC system that incorporates variable frequency drive (VFD) with scheduling control can deliver significant energy savings, especially when deployed at scale along with a building intelligence solution offering predictive and proactive controls for incremental adjustments for variable loads.
In many states and cities, VFDs are required by building code on rooftop units (RTU) and air handling units (AHU) of nine tons or greater. HVAC systems are designed to cater to the peak design load of a building. However, most of the days the building experiences partial loads, either because of milder weather or lower than maximum occupancy load. VFDs offer higher efficiency during partial HVAC load scenarios. VFDs also help reduce inrush current at startup, plus lowered mechanical stress.
In AHU's with variable loading capacities, the 75F CCU will continuously adjust both the chilled water supply as well as fan speed to accommodate the building load. Such equipment can take advantage of the small granular control in capacity between 0-100% that the 75F system can offer.
However, 75F is often deployed with simpler HVAC equipment with only 1 or 2-stages of cooling or heating. In such a case, we follow an approach that modulates the fan speed based on 3 primary positions for 2-stage RTUs.