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N°2 – Two pipe/two wire FCU feed supply training – A level

This system has only one chilled water network, the heating coils being fed electrically.

To limit balancing problems, the chilled water network can be fitted in a Tichelmann loop. All the cooling coils must however be fitted with balancing valves.

Note :
Remember that the Tichelmann loop only permits equal share distribution of pump flow when the connected elements and valves are of the same type.
As a result, if the network has different models of fan coils, the Tichelmann system is of no use. The distribution will be of classic two pipe type and thus obviously balanced.
If all the fan coil units are the same model, but have to supply different outputs, the Tichelmann system could be justified. However the distribution has to be balanced. It permits each unit to receive the required flow for its desired power output.

To avoid the heating coil working at the same time as the cooling coil, the regulating of each FCU must have a neutral segment of a few degrees on the ambient temperature control.

Diagram example in sequence of the regulating of a 2 pipe/2 wire FCU.

  • If the room temperature rises above 20 [°C] (68°F), the electric coil is switched off (all or nothing signal type).
  • If the room temperature rises above 25 [°C] (77°F), a demand for (progressive) opening of the control valve of the cooling coil is sent.
  • Between 20 and 25 [°C] (68 and 77°F) the electric coil is off and the cooling coil is not fed. We speak of « neutral zone or “deadband”».

The output control valves of cooling coils can be of either 2 or 3 way types.

Coil controlled by a 2 way valve                                Coil controlled by a 3 way valve

Note:There are also ‘4 way’ valves which facilitate coil connection. They operate in the same principle as 3WV (variable flow in the coil).