Economizer Mode is an HVAC control strategy that uses outdoor air to cool buildings when outdoor temperatures fall below indoor setpoint temperatures, reducing mechanical cooling energy consumption. This free cooling approach is one of the most effective energy conservation strategies for commercial buildings.
Technical Operation
Economizer systems monitor outdoor air temperature and enthalpy (moisture content), automatically increasing outdoor air damper position when conditions are favorable for cooling. Most systems activate when outdoor temperatures fall below 55°F or outdoor air enthalpy drops below 28 BTU/lb. Mechanical cooling compressors are modulated down proportionally as outdoor air cooling contribution increases, with the system switching to full mechanical cooling when outdoor conditions become unfavorable.
Control Requirements
Proper economizer operation requires outdoor and return air temperature sensors, outdoor air quality monitoring, and damper position feedback. Building codes such as IECC 2021 and ASHRAE 90.1 mandate economizers on all rooftop units and 5,000-cfm systems. Systems must prevent short-circuiting of outdoor air to exhaust dampers.
Energy Impact
Economizer operation reduces cooling energy consumption by 20-40% annually in temperate climates by providing free cooling during 4-8 months yearly. Proper commissioning is critical, as improperly tuned economizers can increase energy consumption.