Feature Notes
Air Handing Unit Fan Changeover Submodule with 3 x Triac Outputs
FCO / DIN / AHU / 3T / ...
Main Features Automatic Changeover of Twin Supply or Extract Fans Automatic Duty Rotation Changeover on Airflow Failure Automatic Interlocks with AHU

Description of Features

General

This Fan Changeover Module is an AHU Submodule, and must be used in conjunction with a SeaChange AHU Controller; it can be used to control Twin Supply Fans or Twin Extract Fans ( the correct variant must be selected - see “Product Codes”). A Volt-free contact airflow status signal must be provided, either individual signals for each fan or a common signal for the pair; these signals can be derived from flow switches measuring flow directly, or Contactor Status signals derived in the control panel.

Other Changeover modules are available to provide the same changeover function for fans unrelated to AHUs (e.g. Toilet Extract fans with no supply AHU). See “Changeover Module” Data Sheet.

Changeover operation

The Command to run the fan pair is received from the AHU Controller to which the Changeover Module is registered (see “Registration”). When the run command is received, the fan which has been turned off for the longest time will be started; by this means, fans are automatically rotated every time the fans start.
A Flow Proving Delay (or Grace Time) is allowed for airflow to become established, this may be adjusted by using Configuration Parameter DLAY ; if flow is still not indicated by the flow switch / contactor auxiliary signal after this delay, the duty fan will be stopped and the standby fan will be started.
If the standby fan also fails to start (after the Flow Proving Delay has elapsed) the module will enter its Failure Mode; what happens to the fan outputs in this mode can be selected using the FMDE. Either both fans will run, the last to run will continue to run, or both will be shut down awaiting a manual reset using the Override button. The Changeover sequence described above will also occur if a failure occurs at some time after initial startup.

On receipt of a command to run the fan, the fan which has been off longest will be started, if after the flow proving 'delay' (set by config variable DLAY, default 5 seconds) neither of the two inputs have been made then the first fan will be stopped and the other fan started. This condition is indicated by the top LED alternating red and green. If again no proof of flow is received then this is indicated by the top LED flashing red. The fan action for this failure mode is modified by the configuration variable FMDE, allowing both fans to run(1), last one to run(2) or switch both off(3) dependant upon the requirements of the installation.

If a fan has failed then the third relay will be energised allowing connection to an annunciator.

The error condition is reset by the flow proving signal being reinstated or by the command signal being removed, i.e. it will start with no error at commencement of the next occupied period. The error condition can also be manually reset by pressing the 'Override' button.

During normal operation the top LED will be steady green, the lower status LED will show green if the controlling device 'is occupied'.

Interlocks with AHU Fans

The AHU Controller determines when the fans will run; it sends a demand signal to the Changeover Module. When airflow is established (see “Changeover”) the Changeover Module signals to the AHU Controller, which will then complete its start-up sequence (see AHU Data Sheet for full details).

If airflow has failed, and the Changeover Module has entered its Failure Mode, it will signal the AHU Controller, which will either shut down awaiting a manual reset, or will attempt to restart after a time delay. The Restart Delay Parameter in the AHU Controller is used to determine whether the AHU will automatically restart, or await a manual reset.

Registration

Registration is the simple process by which logical connections are made between Controllers in a SeaChange system; it is done at time of commissioning and involves pressing buttons on the Controllers in a specific sequence (for further details of the registration process, see our publication “Commissioning Guide”).
The Changeover Module must be registered to an AHU Controller; this is done by putting the AHU Controller into Configuration Mode, and registering the Changeover Module to it. This automatically enables all necessary demand signals, interlocks, etc. to be exchanged between the Controllers across the network.

Up to 2 Changeover Modules may be registered to an AHU Controller

The module is registered to it's AHU controller by putting the AHU controller into config mode and then pressing the registration button on the Fan Changeover module. Registration is confirmed by the status LED on the module flashing once. One or two FCO modules can be used with each AHU controller. The config variable TYPE needs to be set to select Supply or Extract as needed.

The AHU controller must be AHU3b (AHU3ah) or later to support a FCO module

ChangeOver on Hours Run

The controller will automatically change the fans over if the continous run time exceed the setting of Maximum Hours Run MXHR. This is set to 24 by default.

Alarms

The module can generate networked Alarms for failure of either fan If both fans fail then the AHU will generate a Fan Fail alarm in addition to the alarms generated by the FCO module. The AHU will shut down and will not restart until the override button has been pressed or the AHU is reset by clearing switch3 to zero.

The Changeover Module may be set to not report alarm conditions or report them to a SeaChange Doorway Supervisor (either locally connected to the system, or via an autodialling modem). The ALRM parameter is used to select the desired Alarm Mode, whilst ALST is used to set the sense (ie. whether a closing or opening contact indicates Airflow) of the Fan status signal(s).

The Changeover Module generates 3 alarm conditions:

Note that the ALRM parameter affects only the reporting of alarms to a Supervisor; the AHU will shut down if both fans fail irrespective of the setting of ALRM.

Sensors and Plots

The run hours for each fan are available as sensor1 and sensor 2 and these are plotted for the last 96 days using the normal Doorway plots. The stored hours run for each fan can be reset using Switches 3 & 4. The maximum hours counted before roll over is 9999 hours.

Options and Product Codes

Air Handling Unit Fan Changeover Submodule

FCO / DIN / AHU / 3T / [driver option]

Driver options

If a single flow switch or status signal is used, wire into either 3&4 or 5&6.
Do not use Trip signals.

SC Controls Ltd

PO Box313
Wadhurst
East Sussex
TN5 6JL

phone 08707 606040
fax 08707 606041
e-mail seachange@sccontrols.co.uk
http:// www.seachange.co.uk