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N°3 – Two pipe FCU feed supply, network known as “Change Over” training – A to HND level

Fan coil units technology N°3 – Two pipe FCU feed supply, network known as “Change Over” training – A to HND level

In the systems known as « change over » systems, the two pipe fan coils (one lone coil per unit) are connected to a two pipe network, fed either with chilled or heated water.
The coil is generally sized to cover cooling needs and is thus over-powered in heating mode.

The change over between heating and cooling mode happens at the same time for all the fan coils by moving the changeover valves. These valves can be motorised but generally they are manually controlled.
This type of distribution, in which all the FCU are either in cold mode, either in hot, makes managing mid-season periods difficult if the various room loads are not sufficiently similar. During the design stage, it is possible to regroup the fan coils by similar load zones (see figure below) that we change from hot or cold mode by manual or automatic local changeover valve adjustment.

Question  


Print out the distribution diagram above.
Indicate, with arrows, the circulation in the pipe work which is fed when all fan coils are in heating mode (cooling unit off).
 Specify on the 3WV the ports which are open and which are closed (C).

All fan coil units are demanding heat.

Question  

Print out the distribution diagram above.
Indicate, with arrows, the circulation in the pipe work which is fed when all fan coils are in cooling mode (heating unit off).
 Specify on the 3WV the ports which are closed (C).

All fan coil units are demanding cooling.

Question  

Print out the distribution diagram above.
Indicate, with arrows, the circulation in the pipe work which is fed when all fan coils of the east façade are in cooling mode and those of the west in heating mode.
 Specify on the 3WV the ports which are closed (c).

The east facade demands heating; the west facade demands cooling.


The pilot control of the single 2 way valve will have a “winter” and a “summer” pilot scheme. It will be informed of the change from hot to cold mode by a signal from a bus. Before, each control was informed of the change by the local distribution temperature control.

Sequential diagram of the regulating of a 2 pipe fan coil unit

  • If the temperature of the room drops below 20 [°C] (68°F), a demand for (progressive) opening of the control valve of the heating coil is sent.
  • 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 regulating valves are closed and the cooling coil is not fed (neutral zone or “deadband”).
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