A fan coil unit (FCU) contains a fan which draws the air in a space into the unit then blows it over a cooling or heating coil. The air comes out of the FCU either cooler or hotter than before. They are used in some office buildings and shopping centers and typically specified where there are multiple small spaces requiring individual control. Typically an individual FCU serves only up to 150m², so there can be tens or even hundreds in a building. FCUs are, however, most commonly used as a supplement to a building for which other HVAC systems provide the majority of the air-conditioning.
FCUs will generally have a chilled water coil for cooling and either a hot water coil for heating or an electric heating element. Chilled water is provided from a chiller located in the central plant, and hot water from a boiler. Each FCU is provided with a small supply of outside air to ensure adequate ventilation.
High level of flexibility in terms of subdivision and rearrangement of space.
Poorly suited to open plan spaces, as adjacent units can operate in conflict.
Does not generally have the ability to use outside air for free cooling, making the system less efficient in cooling particularly in spring and autumn.
Chilled water valves and hot water valves in the ceiling can be a maintenance problem.
AHUs are usually connected to a central HVAC system whereas an FCU can function or be installed itself. AHU is the bigger HVAC system not to mention, the FCU is also regarded as the smaller version of the AHU. In this regard, the smaller FCUs can be called terminal units. The latter usually does not have any duct system that’s why it is obviously smaller in size as previously mentioned. It is only composed of a simple coil and fan.
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