Outdoor air brings moisture that the ventilation path must handle.
A dedicated outdoor-air system moves the required ventilation air through filters and a cold coil that condenses moisture. Reheat may then adjust supply temperature, allowing the room system to focus on the remaining sensible load.
Follow the airflow through the equipment.
Outdoor air
The supply fan brings the required ventilation air into the unit through an intake and filters.
Cooling and condensation
A cold coil lowers the air temperature so part of its water vapour becomes condensate.
Reheat
When the design uses reheat, the dry air is warmed toward a suitable supply condition.
Delivery
The fan sustains flow through the complete unit and downstream distribution path.
What the fan is responsible for
- Maintain outdoor airflow across clean and loaded filters and wet coils.
- Provide pressure for internal sections, dampers, ducts, diffusers and controls.
- Follow the required airflow command without confusing fan speed with measured ventilation flow.
Why the route matters
- A wet or dirty coil changes pressure loss and the fan operating point.
- Air bypassing the coil carries moisture downstream without the intended treatment.
- Poor condensate management or reheat control can defeat the supply-air condition.
Define these inputs before choosing a fan
A LONGWELL route to evaluate: backward-curved EC centrifugal fans
LONGWELL backward-curved EC fans are a pressure-capable route to evaluate for a DOAS supply path. Compare the fan at the full installed system curve, including final filter and wet-coil conditions, then confirm controls, sound, access and environmental exposure.
Verify the complete equipment, not the fan in isolation
Bring the outdoor-air duty and the complete unit pressure path.
Share design conditions, airflow, final resistance and control requirements so LONGWELL can review a fan candidate.