With people's continuous understanding of fan coil units, they began to know that there are 4 pipe fan coil unit and 2 pipe fan coil unit. What are the differences between these two different types of fan coil units, and what are the differences in wiring?

In fact, the control fan coil here does not refer to the coil itself, but refers to the system piping.

What is a 4 pipe fan coil unit?
The cold and hot water supply pipes and the return pipe of the 4 pipe fan coil unit are independent systems, which can supply heat while supplying cold. The two systems do not interfere with each other and can be switched at any time. The system is installed with a switching control valve when the water inlet and outlet pipes are installed, and the switching valve is controlled by a temperature regulating valve to regulate the cold and hot water quantity, thus realizing refrigeration or heating.

What is a 2 pipe fan coil unit?
The 2 pipe fan coil unit system is a set of pipes for cooling and heating. If the four seasons are distinct, there will be no need for both cooling and heating. Therefore, the 2 pipe fan coil unit system should be more. This design can not only save investment, but also be very convenient for maintenance.
From the above analysis, it can be seen that the 4 pipe fan coil unit and 2 pipe fan coil unit are mainly system differences, and the wiring is certainly different.

What is the difference between the wiring of 4 pipe fan coil unit and 2 pipe fan coil unit?

Two-control control scheme: it is controlled by the combination of temperature controller and three-wire electric valve, and the comparison between the set temperature of the temperature controller and the measured temperature is used to signal the opening/closing of the electric valve.

Four-control control scheme: it is controlled by the combination of temperature controller, cold water valve and hot water valve. In cooling mode, the hot water valve is in closed state and is not controlled unless the temperature controller changes the mode to heating mode.  In contrast, in the heating mode, the cold water valve is closed and is not controlled unless the thermostat changes the operating mode to the cooling mode.