This large outdoor unit exhausts 13,500 CFM through a wheel to recover energy. The remaining return air is recirculated and mixed with 13,500 CFM of outside air. This mixed air passes through a cooling coil / high capacity gas heater as it is supplied to the space.
In economizing mode, the recirculation damper and minimum outside air dampers both shut. All 45,000 CFM of outside air is pulled in through the side dampers on the unit, while 45,000 CFM of exhaust air is bypassed around the wheel and exhausted from the unit.