When outdoor air is cool enough, the outdoor damper opens, the return damper closes and the relief damper lets excess air out, so mechanical cooling is reduced or off. Changeover is decided by outdoor dry bulb, enthalpy or a comparison with return air. Economizers that are stuck, badly wired or using failed sensors are common and can waste more energy than they save, which is why they are tested at commissioning.
Economizer's stuck at 100 percent open on a 95 degree day, the RTU's trying to cool the whole outdoors.
Test economizers every season; a damper stuck open in summer loads a rooftop unit with hot outdoor air it was never sized to handle.
Also heard as
- econ
- airside economizer
Related terms
RTU
Rooftop unit: a packaged air conditioner, often with gas heat, that sits on a roof curb and ducts straight down into the building.
Damper
A blade or set of blades in a duct or opening that controls, balances or shuts off airflow.
Enthalpy
The total heat content of moist air, sensible plus latent, in Btu per pound of dry air.
Ventilation rate
The amount of outdoor air deliberately brought into a space to dilute indoor contaminants, usually in cfm per person and per square foot.