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N°4 – Four pipe FCU feed supply training – A level

Two twin pipe networks, hot and cold, possibly Tichelmann system, will feed the coils, regulated by 2, 3 or 4 way valves.


Compare the advantages and disadvantages of 4 pipe systems and 2 pipe systems fed by one single distribution circuit.

Left schema: Two pipe FCU Coil controlled by a 2 way valve                           

Right schema: Four pipe FCU Coil controlled by a 2 way valve

The two pipe systems fed by a single circuit are less costly than 4 pipe systems, but the rooms can only be heated or chilled simultaneously.

In addition, in 2 pipe systems, the single coil is perhaps not correctly sized for both heating and cooling requirements. In general, the coil sized for cooling needs is overpowered in heating mode.

Finally, if a balancing is carried out in 2 pipe mode, it will be generally for cooling mode and thus cannot be perfect in heating mode.