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Components of the fan coil unit system: Fan coil unit； Inlet and outlet valves ； Y-type filter ； Solenoid valve/water valve ； Control Panel ； Return air ducts and outlets, insulation ； Fresh air duct ； Water pipes, flexible metal hoses. Advantages and disadvantages of fan-coil units: Advantages: Small size, high efficiency, low noise, low energy consumption. The unit has a sophisticated design; it is compact and durable. The coil is made from high-quality galvanized steel, while the condensate tray is formed through molding processes, resulting in no welds or solder joints. Insulation materials that meet fire safety standards are used to connect everything together with the tray. Disadvantages: Since this method relies solely on convective heat transfer, it fails to achieve an optimal level of comfort indoors; therefore, it is only suitable for places where people stay for short periods of time, such as offices and hotels, and not for ordinary residences. Due to the addition of fans, air ducts need to be installed, which increases costs and operating expenses; moreover, the maintenance and management of the equipment are more complex. Principle of fan coil units: A fan draws in indoor air or mixed outdoor and indoor air, cools or heats it using an evaporator coil, and then sends it back into the room, thereby lowering or raising the indoor temperature to meet people’s comfort requirements. 1. The hot air inside the room is absorbed by the cold water in the fan coil, with the heat being transferred to the cold water ； 2. The refrigeration unit performs work to transfer heat from the cold water to the cooling water ； 3. The heat from the cooling water is transferred to the ambient atmosphere through spraying and vaporization in the cooling tower. Control method: Simple control: A three-speed switch is used to manually control the three speed settings and the start/stop of the fan. Temperature control: Automatically controls the opening and closing of the electric two/three-way valve based on the comparison and calculation between the set temperature and the actual measured temperature ； It directly controls the three-speed switching and start/stop of the fan, thereby achieving a constant temperature by regulating the water flow or air volume through the control system. Classification: By format: horizontal concealed type, horizontal exposed type, vertical concealed type, vertical exposed type, and cartridge type – a total of five types. By thickness: ultra-thin type and standard type. By presence of a condensate pump: standard type and luxury type. By static pressure of the unit: 0Pa, 12Pa, 30Pa, 50Pa, 80Pa (static pressure outside the unit). By number of heat exchange tubes: two-tube type and three-tube type. By system configuration: two-channel type and four-channel type. Note: The term “number of rows” referred to in fan coils denotes the number of rows of copper tubes in the coil’s air-cooling element; generally, two rows means there are two rows of copper tubes, with 8 tubes in each row, for a total of 16 copper tubes ； Three rows mean three rows of copper tubes, 8 tubes in each row, for a total of 24 copper tubes. The more copper tubes there are, the better the cooling effect. Two-stage control: In summer, ordinary fan coils use cold water for cooling, while in winter they use hot water for heating. Four-way control: Commonly used in more luxurious venues, it allows hot and cold water to flow simultaneously, enabling some rooms to be cooled and others heated as needed. Impact of parameter changes on performance: 1. When the air volume of the fan coil unit remains constant and the supply water temperature is fixed, the cooling capacity changes as the supply water volume changes. According to performance statistics for some fan coil unit models, when the supply water temperature is 7°C and the supply water volume is reduced to 80% of its original value, the cooling capacity remains at around 92% of its original level; this indicates that changes in the supply water volume have a relatively slow effect on the cooling capacity. 2. The temperature difference between the supply and return water of the fan coil unit remains constant; as the supply water temperature increases, the cooling capacity decreases. According to statistics, for every 1°C increase in the supply water temperature, the cooling capacity decreases by about 10%; the higher the supply water temperature, the greater this decrease, and the dehumidification capacity declines as well. 3. When the water supply conditions remain constant and the air volume of the fan coil changes, the cooling capacity and the enthalpy difference in air treatment also change; generally, the cooling capacity decreases while the enthalpy difference increases, with little change in the power consumption of the fan per unit of cooling capacity. 3. When the temperature difference between the inlet and outlet water of the fan coil unit increases, the water flow rate decreases, and the heat transfer coefficient of the heat exchange coil also decreases as a result. Furthermore, the heat transfer temperature difference also changed; as a result, the cooling capacity of the fan coil unit decreases as the temperature difference between the supply and return water increases. According to statistics, when the supply water temperature is 7°C, an increase in the temperature difference between the supply and return water from 5°C to 7°C can result in a reduction in cooling capacity of around 17%. Selection of fan-coil units: Fan-coil units have two main parameters: cooling (heating) capacity and air delivery volume. Therefore, there are two methods for selection. First, selection based on the room’s air circulation volume: the product of the room’s area, ceiling height (after the ceiling is installed), and the number of air changes per hour gives the room’s air circulation volume. The fan coil model can be determined by using the circulating air volume corresponding to the high and medium speed air volumes of the fan coil. II. Selection based on the required cooling load of the room: Based on the load per unit area and the room’s area, the required cooling load for the room can be determined. By matching this value with the cooling capacity of the fan coil unit, the appropriate model of the fan coil unit can be selected. Common fault symptoms of fan-coil units: Noise problems caused by the fans and methods for dealing with them: 1. Noise resulting from damaged bearings ； The solution is to replace the bearing. 2. Noise generated during operation in conjunction with the ceiling ； The solution is to adjust the height of the coil suspension bolt nut, or address the friction between the air outlet and the ceiling joists. 3. Noise caused by air in the pipes ； The solution is to exhaust the air from the pipes using the coil exhaust valve, floor exhaust valve, and end exhaust valve. Symptoms and solutions for the issue of a fan failing to start or running at a low speed: 1. Damaged temperature switch ； Use a test pen to check whether there is power at the input terminal of the temperature control switch and at the output terminal of the fan. If it is determined that the temperature switch is damaged, it can be replaced or repaired. 2. Slow operating speed: a. Check whether the surface temperature of the fan is normal; b. After shutting down the fan, manually rotate the blades to see if they turn smoothly. If there is resistance, replace the fan bearings; c. If manual rotation proceeds normally, replace the starting capacitor; d. Measure the resistance of the motor coils; if it’s abnormal, replace the motor. Poor or no cooling effect: 1. Open the coil exhaust valve and check whether the system’s circulating water temperature is normal ； 2. Check the inlet and outlet temperatures: a. If the temperature difference is very small, open the exhaust valve of the coil to check whether the water temperature is normal. If the water temperature is normal, then check whether the two-way valve is open; if it isn’t open, verify whether the power supply to the two-way valve is functioning properly, as well as whether the Y-shaped filter is clogged. b. If the temperature difference between the inlet and outlet is within the normal range, check whether the room’s insulation is adequate, such as whether the doors and windows are closed. If they aren’t closed, air convection will reduce the effectiveness of the air conditioner, and it’s necessary to explain this to the customer. c. If the temperature difference between the inlet and outlet is large and the airflow at the outlet is low, check whether there is dust on the inlet filter and whether the fan’s rotation speed is normal. The air conditioner has an unpleasant odor: 1. Check and clean the air intake filter ； 2. Check whether there is dust on the fins of the coil; if so, a cleaning procedure should be carried out ； 3. Check the air ducts for any foreign objects, dust, water accumulation, etc., and clean them to remove unpleasant odors. 4. Check the water collection tray for any foreign objects. Air conditioner leaking water: 1. Poor drainage – a) Check whether the water collection tray is blocked, b) Check whether the drainage pipe is blocked, c) Check whether the slope of the drainage pipe is appropriate. 2. The insulation layer has fallen off; restore the insulation layer. 3. The exhaust valve is leaking; tighten it. 4. If the hoses, valves, or fittings are leaking, close the main valve before replacing them. Emergency handling for a ruptured air-conditioning water pipe: 1. Open the drain valve to release water and reduce pressure ； 2. Turn off the air conditioning unit, the make-up water valve of the expansion tank, the pressure pump, and the circulation pump ； 3. Close the main valve in the pipe rupture area ； 4. Turn off the power to the area where the pipe has burst ； 5. In case of danger to the elevator, turn off its power supply and try to stop it on a floor above the level where the pipe might burst ； 6. Move important supplies away in a timely manner and clear standing water.