Fan coil unit

Air handling units (AHU, sometimes referred to as ‘air handlers’) form part of the heating, ventilating and air conditioning system (HVAC) that supplies, circulates and extracts air from buildings. Generally, they are connected to the ductwork that supplies air to and extracts air from the interior and can provide ventilation, heating, cooling, humidity control and filtration. For more information see Air handling unit.

Fan coil units (FCU) consist of only a fan and a heating or cooling element, are located within the space they are serving, and are generally not connected to ductwork. They may either just recirculate internal air, in which case a separate ventilation system is required, or may introduce s proportion of ‘fresh’ air that is mixed with the recirculated air.

Fan coil units can be wall-mounted, freestanding or ceiling-mounted and may be concealed in ceiling voids. They may be controlled by local thermostats or by a building management system (BMS).

Due to their simplicity, fan coil units are more economical to install than ducted air handling units. However, they can be noisy and can create vibrations because the fan is in the occupied space.

Where fan coil units are supplied with chilled water and hot water from central boilers and chillers they are generally referred to as two pipe (either heating or cooling) or four pipe (both heating and cooling) units.

Where the heating and cooling is provided locally, they may be referred to as variable refrigerant volume (VRV) or variable refrigerant flow (VRF) systems. Here, refrigerant is circulated between one or more fan coil units and is connected to an external heat exchanger. These systems may be more prone to refrigerant leakage than units that are connected to hermetically-sealed central chillers.

Fan coil units are relatively compact and straightforward to install. However, they require regular maintenance to ensure continued efficient operation.

When a fan coil unit cools air, it will generally cause condensation which must be collected and drained or pumped away.

NB Illustrated Guide to Mechanical Cooling (BG 1/2010), written by Kevin Pennycook and published by BSRIA in 2010, defines a fan coil unit as: ‘A device mounted in the ceiling void or floor mounted often at the perimeter of a building which comprises a fan, a heating coil, a cooling coil and an air filter housed in a metal casing. The fan coil unit is supplied with fresh air via a ductwork distribution network from a central plant. The fan draws a combination of room air and fresh air through the filter and across the heating and cooling coils. The air then passes into a plenum which, for units mounted above false ceilings, has multiple outlets for connection to one or more supply diffusers. Low pressure hot water and chilled water is distributed via pipework to each fan coil unit.’

[edit] Related articles on Designing Buildings

• Air conditioning.
• Air handling unit.
• Building services.
• Building services engineer.
• Chilled beam.
• Chiller unit.
• Constant air volume.
• Fan coils.
• Fan coil refurbishment for improved operational efficiency.
• Heating.
• How does a chilled water fan coil unit work?
• HVAC.
• Mechanical ventilation.
• Mechanical and electrical (M&E).
• Natural ventilation.
• Thermal comfort.
• Variable air volume.
• Variable refrigerant flow.
• Ventilation.

[edit] External references.

• CIBSE TM43 Fan Coil Units.