“A fan coil unit (FCU) is a type of heating, ventilation, and air conditioning (HVAC) equipment commonly used in buildings to provide localized temperature control. It consists of a heat exchanger coil, a fan, and control components. The FCU is typically installed in individual rooms or zones and is connected to a central HVAC system.
How it works:
Heat Transfer: The FCU’s heat exchanger coil can be used for both heating and cooling. If the system is set for heating, hot water from a central boiler or other heat source is circulated through the coil. If cooling is required, chilled water is circulated instead.
Air Circulation: The fan in the FCU draws the room air over the heat exchanger coil. As the air passes over the coil, heat is exchanged between the air and the water in the coil. In heating mode, the coil transfers heat to the air, warming it before distributing it back into the room. In cooling mode, the coil absorbs heat from the air, cooling it before returning it to the room.
Temperature Control: The FCU is typically controlled by a thermostat in the room. When the desired temperature is reached, the thermostat signals the fan coil unit to adjust the flow of hot or chilled water through the coil to maintain the desired temperature.
Number of pipes used:
The number of pipes used in a fan coil unit system depends on whether it is a 2-pipe system or a 4-pipe system.
2-pipe system: In this configuration, a single set of pipes supplies either hot water for heating or chilled water for cooling to all the FCUs in the building. The system can only provide either heating or cooling at any given time, depending on the season. So, if the building needs both heating and cooling capability, the system must be switched between the two modes at different times of the year.
4-pipe system: This setup uses two separate sets of pipes—one for supplying hot water for heating and another for supplying chilled water for cooling. Each FCU has both hot and chilled water connections. This allows the FCUs to provide both heating and cooling simultaneously, providing better comfort and flexibility. However, it requires more complex installation and increased infrastructure cost compared to the 2-pipe system.
Valves:
In both 2-pipe and 4-pipe fan coil unit systems, various types of valves are used to control the flow of hot and chilled water to the FCUs. The specific types of valves used can vary depending on the system’s design and the manufacturer’s preferences. Some common types of valves used in these systems include:
Two-way control valve: Used to control the flow of water to the heat exchanger coil in the FCU. It modulates the water flow to regulate the amount of heating or cooling provided by the unit.
Three-way control valve: This type of valve is used in 4-pipe systems to control the flow of hot water, chilled water, or a mixture of both to the heat exchanger coil, depending on whether heating, cooling, or simultaneous heating and cooling are required.
Motorized valve: These are automated valves that can be controlled remotely, often linked to the building’s automation system, allowing for precise and efficient control of the fan coil unit’s operation.
The selection of valves and their configuration depends on the specific requirements of the HVAC system and the desired functionality. Consulting with HVAC engineers and professionals is essential for designing and installing an effective and energy-efficient fan coil unit system.”