A fan coil unit, often abbreviated as FCU, is a key component of central air conditioning systems. It is responsible for regulating indoor temperature and humidity to provide a comfortable environment. The basic structure of a fan coil unit includes a coil, a fan, a controller, and an enclosure. The coil is the core part used for heat exchange; the fan drives air flow to increase heat exchange efficiency; the controller regulates temperature and humidity to ensure indoor air comfort; and the enclosure protects the internal components and also provides an aesthetic effect. [^17^]
Fan coil units have been widely used in various buildings such as residential, commercial, hospitals, schools, and factories. Their performance directly affects the operation of the air conditioning system. The development of fan coil units has been driven by advancements in building energy-saving technologies, the expansion of new application areas, and increased policy support. In China, the industry has grown rapidly, with the output value increasing from approximately 5.65 billion yuan in 2018 to 9.73 billion yuan in 2022, representing a compound annual growth rate of 11.8%. [^19^]
Fan coil units are used to regulate the temperature and humidity of indoor air, providing a comfortable environment. They are widely used in commercial buildings, offices, hospitals, schools, and residential buildings. [^16^]
The working principle of a fan coil unit is based on the heat exchange between air and refrigerant. This heat exchange process is achieved through forced convection driven by the fan. In cooling mode, low-temperature, low-pressure refrigerant enters the coil and exchanges heat with the indoor high-temperature air, cooling the air. In heating mode, high-temperature, high-pressure refrigerant enters the coil and exchanges heat with the indoor low-temperature air, heating the air. [^17^]