Fan Coil Unit: The Workhorse of Chilled Water Cooling
A fan coil unit is a small terminal unit containing a fan, a coil fed with chilled or hot water, and a filter. It conditions the air of the space it serves without providing outdoor air, so a separate fresh air supply is required. FCUs give room-level control and are typically concealed above ceilings.
By Dhruv Agarwal · · 2 min read
Why it matters on a project
Fan coil units are the part of an HVAC system occupants interact with most and notice only when something goes wrong — a ceiling stain, a hum in a meeting room, a room that never quite cools.
Almost all of those outcomes are decided during installation and coordination, not during equipment selection.
What is inside one
| Component | Function | Where it causes trouble |
|---|---|---|
| Fan | Moves room air across the coil | Noise, especially if oversized |
| Coil | Chilled or hot water heat exchange | Fouls if the filter is neglected |
| Filter | Protects the coil, cleans recirculated air | Needs routine, easy access |
| Drain pan and trap | Collects and removes condensate | Leaks, ceiling staining |
| Control valve | Modulates water flow to the coil | Control quality, energy use |
The three details that decide satisfaction
Condensate drainage. Correct continuous fall, a properly formed and primed trap, and no dips. This is where most FCU complaints originate.
Access. A correctly sized access panel directly below the unit. If filters are awkward to change, they will not be changed.
Noise. Check sound data against the room's requirement, particularly for meeting rooms and cabins. An oversized unit running at high speed to meet a control setpoint is noisier than a correctly selected one.
Fresh air is separate
An FCU conditions air; it does not ventilate. Outdoor air for occupants comes from a separate treated fresh air supply, sized against the ventilation rates adopted for the project — commonly referenced to ASHRAE 62.1, within the framework of NBC 2016, Part 8.
Equipment efficiency and control requirements for commercial buildings are addressed in ECBC 2017. Selection and sizing are the MEP consultant's output.
Common mistakes
- Omitting the fresh air system. The building cools and still feels stale.
- Condensate runs with inadequate fall. Produces ceiling stains, usually months after handover.
- Token access panels. Maintenance that is difficult does not happen.
- Selecting on capacity without sound data. Meeting rooms suffer most.
- Oversizing. Short cycling, poor humidity control and more noise.
- Moving units during ceiling coordination without rechecking drains. The fall that worked on the original layout may not survive the new position.
Standards referenced
Building services provisions in NBC 2016, Part 8; ventilation rates commonly referenced to ASHRAE 62.1; HVAC equipment and control requirements in ECBC 2017. Equipment selection, sizing and system design must be established by the project's MEP consultant.
Standards referenced
- NBC 2016, Part 8 — Building services — air conditioning and ventilation
- ASHRAE 62.1 — Ventilation for acceptable indoor air quality
- ECBC 2017 — HVAC equipment and controls