ACCX changeover for AHU
CMR Electrical Ltd
Bolton House
Five Chimneys Lane
Hadlow Down
East Sussex
TN22 4DX
Tel: 01825 733600
Air Conditioning Run & Standby Controller Type ACCX
The ACCX has been designed to control two air handling units and allows one unit to provide heating /
cooling with the second unit in standby. After an adjustable time delay which can be set between 1 and 999
hours, the run AHU will stop and the standby AHU will start up. This feature allows even ware of both
AHUS.
In the event of a fault developing with the run AHU, the ACCX will shut it down, start the standby AHU,
give an audible warning, operate the common internal alarm relay and display the nature of the fault in Text
on the alpha numeric display. The system would remain in this configuration until the faulty AHU had been
rectified and the “Reset” push button operated.
Having changed to the standby unit due to a fault in the run AHU, if the standby unit also becomes faulty
both AHU1 and AHU2 would be asked to start. This will allow both AHUS to provide some heating or
cooling whilst waiting for repair. The ACCX would also inhibit automatic transfer after the preset time
delay, start the audible warning, operate the common alarm relay and display the nature of the fault in Text on
the alp her numeric display. The system would remain in this configuration until the faulty AHUS had been
rectified and the “Reset” push button operated.
A “room over temperature” signal using a standard thermostat located within the room can be connected to
the ACCX. When the thermostat detects an over temperature the ACCX will start both AHUS to give the
maximum cooling to the room. The ACCX will also give an audible warning, operate the common internal
alarm relay and display the nature of the fault in Text on the alpher numeric display. The system would remain in this configuration until the fault had been rectified and the “Reset” push button operated.
The ACCX can also be asked to change from the run to standby unit via fault contacts (providing the units
have this facility) within each AHU. This feature allows a change over to the standby unit before the room
temperature rises to an unacceptable level.
A non volatile memory within the ACCX is provided to store “Time between automatic changeovers” and the
time until the next changeover. In the event of power failure both time periods would remain held within the
unit so that on re-powering the time delay to the next changeover continues from where it stopped i.e. on
power down it was 63 hours to the next changeover, on re-powering up of the system it will still be 63 hours
to the next changeover.
Three push buttons are provided “Mute” to stop the audible warning device, “Reset” to revert the system back
to normal operation after a fault and “Set” used to manually select which unit is to be run unit or change the
time period between automatic changeovers. A timer is activated when entering the “Set” mode which will
automatically revert the system back to normal operation if a push button has not been operated within 10
seconds.
The ACCX allows the user at any time to manually selection which AHU is to be the run unit. This can only
be performed when the system is in normal running with no current faults. Also provided within the ACCX is
a manual override switch for each AHU. This feature allows the user to override the ACCX and run any or
both AHUS for maintenance purposes.
CMR
Specialized Electronic Equipment Manufactures
Electrical Ltd
The unit consists of two volt free contacts (Start/Stop AHU1 & 2) and will control both AHUS. Both contacts
are normally closed, this allows a failsafe for when the unit is powered down or becomes faulty as both
AHUS will start. In normal operation the Run AHU volt free contact will be closed (relay de-energized) and
the standby AHU volt free contact will be open (relay energized). Both AHUS will need to supply an
individual control interlock through the units control relays.
Three fault inputs are provided, “AHU1”, “AHU2” and “Room over temperature”. A four way selector
switch has been provided within the unit to allow the individual fault signals to be set at normally open or
normally closed. Any combination of normally open/closed can be set by this switch, i.e. AHU1 normally
open (close in fault), AHU2 the same and Room over temperature normally closed (open in fault) . This
switch is located on the left hand side of the main PCB. Identification numbers on the switch relate to, “1”=
AHU1 is a normally open input when the switch is pushed to the far left or normally closed when pushed to
the far right, “2”= the same but for AHU2 and “4”= the same but for Room over Temperature (switch “3” is
unused). The control unit will provide a 12vdc signal to all the remote fault contacts which should be volt
free.
A “common” alarm relay is provided which again will be energized in normal operation, de-energize in
alarm. Again, this allows a failsafe for when the unit is powered down or becomes faulty as it will start a
remote alarm if fitted or signal a fault to the BMS due to power failure.
Features
Alphanumeric display for ease of Fault or status identification from a distance
On board audible warning device to alert local operators of a problem
Automatic duty changeover timer adjustable between 1 and 999 hours
Automatic changeover to the Standby AHU if the Run unit becomes faulty
Room over temperature will start both AHUS via external thermostat
Manual selection of the Run AHU at any time
Maintenance override for each AHU allowing work to be carried out on the standby unit
Common fault relay for onward signalling
Fault input from AHUS to force a changeover before room temperature increases
Small size foot print, wall or surface mounted
Specification
Housing type
Mounting
Size
Colour
Input power
Burden
Power termination
Voltage to plant contacts
Connections to plant
Access
Output contacts
Other outputs
Other inputs
ABS Plastic
Wall, flush or surface
200mm wide x 150mm high x 78mm deep
Light grey
50 Hz single phase 230VAC +/- 10%
< 3VA
Internal 3 way terminal block
12VDC
Internal terminal block
Top, bottom or back
1 x Volt Free normal closed 3 amp contact per zone
Open collector for common alarm
Remote Muting of audible warning device
CMR Electrical Ltd Manufactures of Electrical & Electronic Equipment
Continual development may result in products and specifications being changed without prior notice
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