A four-pipe fan coil unit is a terminal air conditioning device commonly used in commercial buildings, hotels, hospitals, offices, and high-end residential projects. It is designed to provide both cooling and heating with high flexibility and independent zone control. The term “four-pipe” refers to the presence of two supply and two return pipes: one pair for chilled water and one pair for hot water. This arrangement allows simultaneous cooling and heating in different areas of the same building, depending on each zone’s specific requirements.The unit typically consists of a fan, a cooling coil, a heating coil, an air filter, a condensate drain pan, and a control system, all enclosed in a compact casing. The fan draws room air through the filter, then forces it across the coils. When cooling is required, chilled water flows through the cooling coil, absorbing heat from the air. When heating is needed, hot water circulates through the heating coil, releasing heat to the air. The conditioned air is then supplied back into the room either directly or through ductwork.Four-pipe fan coil units are usually controlled by a room thermostat or a digital controller. Occupants can set the desired temperature, and the control system modulates the water valves and fan speed accordingly. This allows precise control of thermal comfort and reduces energy consumption by matching output to actual demand. Variable fan speeds further improve comfort by limiting noise levels and avoiding strong drafts.Installation configurations include ceiling concealed, cassette type, floor-mounted, and wall-mounted units. Ceiling concealed models are installed above the false ceiling and connected to diffusers, offering a discreet appearance. Cassette units are mounted in the ceiling grid and distribute air in multiple directions. Floor-mounted or wall-mounted units are more visible but provide easy access for maintenance and are often used in perimeter zones near windows.One of the key advantages of four-pipe fan coil systems is operational flexibility. In shoulder seasons, some areas of a building may require heating while others need cooling. With separate chilled and hot water circuits, the system can serve both needs simultaneously. This is particularly beneficial for buildings with diverse internal loads, such as spaces with high solar gains on one façade and shaded zones on another.Maintenance primarily involves cleaning or replacing air filters, checking the condensate drain, inspecting coils, and verifying valve and control operation. Proper maintenance ensures efficient performance, extends equipment life, and maintains good indoor air quality. When integrated with a building management system, performance and energy use can be monitored and optimized in real time.Overall, a four-pipe fan coil unit provides a versatile, modular, and efficient solution for individualized temperature control, making it a popular choice in modern HVAC designs where comfort, flexibility, and energy performance are important.