Core Division of Labour
A fresh-air unit conditions outdoor air and normally works with fan-coil units, whereas an air-handling unit (AHU) comprehensively treats the air and carries the cooling and moisture load of a zone. The AHU also secures the required fresh-air volume.
Five Key Differences
- Fresh-air units handle outdoor air; AHUs treat the blended airstream
- Fresh-air units usually take no zone load, controlling only supply temperature and humidity
- AHUs perform complex treatment and guarantee fresh-air volume
- AHUs suit large open areas where fan coils cannot be installed
- Fresh-air units pair with fan coils in smaller spaces, complementing each other
How a Fresh-Air Unit Works
A PID controller compares the supply-air sensor reading with the setpoint and drives a motorised valve. Modes switch between cooling and heating; freeze and differential-pressure switches protect the coil and signal filter blockage.
Sections and Selection
- Typical sections: filtration, cooling coil, humidification, fan, UV sterilisation and heat recovery
- Choose type by installation; size airflow and pressure at or above design values
- One fresh-air unit generally serves a single floor