FCUs

Fan coil units (FCUs) are compact terminal air conditioning devices used to condition individual spaces. They consist of a blower or fan and a heating or cooling coil, through which a working fluid circulates from a central plant or a direct expansion system. FCUs do not generate cooling or heating themselves; they rely on a central chiller and/or boiler, or on refrigerant lines, to provide the thermal energy.

FCUs are typically installed in rooms or zones and are controlled by local thermostats or a building management system. They are commonly used in commercial buildings, hotels, and multi‑unit residential structures where separate zoning is desired. In hydronic (water-based) FCUs, the coil is fed by either chilled water for cooling or hot water for heating, often arranged in two-pipe or three-pipe configurations. In two-pipe systems, a single set of pipes handles both cooling and heating, usually switching mode seasonally. In three-pipe systems, heating and cooling coils can be supplied independently, allowing simultaneous control.

Direct expansion (DX) FCUs use refrigerant to cool or heat the air directly at the coil and are connected to a refrigerant circuit rather than a hydronic loop. FCUs may be ceiling-mounted, wall-mounted, floor-mounted, or concealed, and they commonly include air filters and condensate drainage.

Advantages include zoned comfort, compact footprint, and potential energy efficiency through modular operation. Limitations can include higher maintenance needs, potential noise, and reliance on a central plant for energy transfer.