A fan coil unit (FCU) is a simple device consisting of a heating or cooling coil and fan. It is part of an HVAC system found in residential, commercial, and industrial buildings. Typically a fan coil unit is not connected to ductwork, and is used to control the temperature in the space where it is installed, or serve multiple spaces. It is controlled either by a manual on/off switch or by thermostat.
Due to their simplicity, fan coil units are more economic to install than ducted or central heating systems with air handling units. However, they can be noisy because the fan is within the same space. Unit configurations are numerous including horizontal (ceiling mounted) or vertical (floor mounted).
A fan coil unit may be concealed or exposed within the room or area that it serves.
An exposed fan coil unit may be wall mounted, freestanding or ceiling mounted, and will typically include an appropriate enclosure to protect and conceal the floor fan coil itself, with return air grille and supply air diffuser set into that enclosure to distibute the air.
A concealed fan coil unit will typically be installed within an accesible ceiling void or services zone. The return air grille and supply air diffuser, typically set flush into the ceiling, will be ducted to and from the fan coil unit and thus allows a great degree of flexibility for locating the grilles to suit the ceiling layout and/or the partition layout within a space. It is quite common for the return air not to be ducted and to use the ceiling void as a return air plenum.
The coil receives hot or cold water from a central plant, and removes or adds heat from the air through heat transfer. Traditionally fan coil units can contain their own internal thermostat, or can be wired to operate with a remote thermostat. However, and as is common in most modern buildings with a Building Energy Management System (BEMS), the control of the ducted fan coil unit will be by a local digital controller or outstation (along with associated room temperature sensor and control valve actuators) linked to the BEMS via a communication network, and therefore adjustable and controllable from a central point, such as a supervisors head end computer.
Fan coil units circulate hot or cold water through a coil in order to condition a space. The unit gets its hot or cold water from a central plant, or mechanical room containing equipment for removing heat from the central building's closed-loop. The equipment used can consist of machines used to remove heat such as a chiller or a cooling tower and equipment for adding heat to the building's water such as a boiler or a commercial water heater.
Fan coil units are divided into two types: Two pipe fan coil units or Four pipe fan coil units . Two pipe fan coil units have one supply and one return pipe. The supply pipe supplies either cold or hot water to the unit depending on the time of year. Four pipe fan coil units have two supply pipes and two return pipes. This allows either hot or cold water to enter the unit at any given time. Since it is often necesary to heat and cool different areas of a building at the same time, due to differneces in internal heat loss or heat gains, the four pipe fan coil unit is most commonly used.
Fan coil units may be connected to piping networks using various topology designs, such as "direct return", "reverse return", or "series decoupled". See ASHRAE Handbook "2008 Systems & Equipment", Chapter 12.
Depending upon the selected operating conditions, it is very likely that the cooling coil will be designed to de-humidify the entering air stream, and as a by product of this process, it will at times produce a condensate which will need to be carried to drain. The floor fan coil will contain a purpose designed drip tray with drain connection for this purpose. The simplest means to drain the condensate from multiple fan coil units will be by a network of pipework laid to falls to a suitable point. Alternatively a condensate pump may be employed where space for such gravity pipework is limited.
Speed control of the fan motors within a fan coil unit is effectively used to control the heating and cooling output desired from the unit. This is normally acheived by manually adjusting the tappings on an AC transformer supplying the power to the fan motor. Typically this is adjusted at the commissioning stage of the building construction process and is therefore set for life. However alternative means of external speed control by electronic means through the BEMS can be provided if so required. Fan motors are typically AC type motors but more recently DC motors have been made available by some manufacturers, and can potentially offer significant energy savings.
Duct fan coils are typically used in spaces where economic installations are preferred such as unoccupied storage rooms, corridors, loading docks.
In high-rise buildings, fan coils may be stacked, located one above the other from floor to floor and all interconnected by the same piping loop.
Fan coil units are an excellent delivery mechanism for hydronic chiller boiler systems in large residential and light commercial applications. In these applications the fan coil units are mounted in bathroom ceilings and can be used to provide unlimited comfort zones - with the ability to turn off unused areas of the structure to save energy.
In high-rise residential construction, typically each fan coil unit requires a rectangular through-penetration in the concrete slab on top of which it sits. Usually, there are either 2 or 4 pipes made of ABS, steel or copper that go through the floor. The pipes are usually insulated with refrigeration insulation, such as acrylonitrile butadiene/polyvinyl chloride (AB/PVC) flexible foam (Rubatex or Armaflex brands) on all pipes or at least the cool lines.
A unit ventilator is a fan coil unit that is used mainly in classrooms, hotels, apartments and condominium applications. A unit ventilator can be a wall mounted or ceiling hung cabinet, and is designed to use a fan to blow air across a coil, thus conditioning the space which it is serving.
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1.Diversity of Floor Fan coils suitable for different requirement.
