AHU (Air Handling Unit)
An Air Handling Unit (AHU) is the packaged machine that filters, cools or heats, and circulates air for a building zone — a casing containing filters, coils fed by the chilled/hot water plant, and a blower delivering air through ductwork.
Why it matters on an MEPF project
The AHU is where central plant meets occupied space: chilled water from the chiller becomes cold air for the floor. Its selection fixes zone comfort (airflow, coil capacity), hygiene (filtration stages), and running cost (fan power, which ECBC-era design pushes down with better coils and VFD-driven blowers).
AHU rooms are also a space-planning obligation — floor-wise units need builder's-work space, fresh-air paths, drainage and acoustic care. Undersized AHU rooms are one of the classic architect–MEP coordination failures: the unit fits, the maintenance access does not.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Airflow (CMH/CFM) | From zone heat load and air-change requirement | design basis / NBC 2016 Part 8 |
| Coil duty | From room sensible + latent load | heat-load calculation |
| Filtration | Pre + fine filters; HEPA only for clean applications | application spec / ISO 14644 where cleanroom |
| Fan power | VFD-driven, sized against duct static pressure | ECBC 2017 efficiency intent |
Common mistakes
- AHU room sized for the unit, not for pulling the coil or changing filters.
- No condensate trap/slope — the pan overflows into the ceiling below.
- Fresh-air intake beside the toilet exhaust or DG stack.
- Filters specified fine, then never replaced — pressure drop quietly eats airflow.
Related on this site
Frequently asked
AHU vs FCU — what is the difference?
Scale and role: an FCU (fan coil unit) is a small room-level coil+fan; an AHU is a larger zone-level machine with staged filtration and ducted distribution. Big open floors get AHUs; cabins and small rooms often get FCUs.
Why is my AHU delivering less air than design?
Usually loaded filters, slipped belts, or duct leakage — measure static pressure across the filters first. It is the cheapest diagnosis in HVAC.
Standards referenced: NBC 2016 Part 8 · ECBC 2017