Air-Side Economizer Free Cooling & Enthalpy Calculator
Calculate commercial HVAC air-side economizer changeover thresholds, compare outdoor vs return air enthalpy, and quantify free cooling capacity and avoided compressor power per ASHRAE 90.1.
Air Conditions & Psychrometrics
°F
%
°F
%
HVAC System & Control Strategy
CFM
e.g., 5,000 CFM (~12.5–15 Ton RTU).
°F
BTU/Wh
Economizer Damper Operational Status
100% FREE COOLING ACTIVE
Free Cooling Thermal Relief
102,600 BTU/h
8.55 Tons of refrigeration
Avoided Compressor Power
8.92 kW
Instantaneous electrical demand savings
Outdoor Air Enthalpy
18.0 BTU/lb
31.6 grains/lb dry air
Return Air Enthalpy
27.9 BTU/lb
9.9 BTU/lb outdoor advantage
Psychrometric Damper Position & Logic
Damper Commanded State:
100% Full Open (Free Cooling)
Outdoor vs Return Temperature Delta:
-19.0 °F cooler outdoors
Moisture Migration Risk:
None (Outdoor air drier than return air)
ASHRAE Standard 90.1 & Title 24 Requirements
Commercial Energy Code
Air-side economizers are mandatory under ASHRAE 90.1 for cooling systems over 54,000 BTU/hr (4.5 tons). Differential enthalpy prevents economizer operation during warm, humid conditions where high outdoor latent moisture would otherwise overwhelm building indoor humidity control.