Economizer: Answer the following: What does an airside economizer do? When is the airside economizer used in HVAC? How is the economizer an energy saving device? When are conditions "OK to economize"? Energy Recovery Ventilator: Answer the following: What does an ERV do? How is an ERV different than an airside economizer? When is the ERV used in HVAC? How is the ERV an energy saving device? What is the difference between a Sensible ERV and a Enthalpy (total heat) ERV