JOHNSON CONTROLS
24
FORM 100.50-NOM7 (808)
Unit Sequence of Operation
VARIABLE AIR VOLUME
SEQUENCE OF OPERATION
Under Variable Air Volume Operation, the unit will be
controlled from one of two sources:
• 7-Wire Thermostat
• Space Sensor
In addition to the two control methods, a VAV con-
gured unit can also operate “stand-alone” with the only
direct control being the Occupied/Unoccupied signal.
The method of control is as selected as described in the
following sections.
VAV Operation With a Thermostat
When VAV with Thermostat parameter is set to ON, a
Thermostat is used for SAT control.
VAV Operation With a Space Sensor
A Space Sensor is used for control when:
• The VAV with Thermostat parameter is OFF, and
• A Space Sensor is available.
• If a Space Sensor is not available, the controller will
self-congure to Standalone VAV operation.
Standalone VAV Operation
Standalone VAV operation is used by the control
when:
• The VAV with Thermostat parameter is OFF, and
• No Space Sensor is available.
VAV Operating Modes
VAV operating modes have the following common
functions:
• For heating, the Heating Mode Enable parameter
must be ON.
• The VAV Heat Relay binary output is used to fully
open the VAV boxes when heating is ON.
• For cooling, the Cooling Mode Enable parameter
must be ON.
• Cooling (compressor) stages are controlled as
described in the following sections.
• The SAT control algorithm for cooling is de-
scribed in the following sections.
• The Supply Fan is:
• Controlled as described in the Fan.
• 100 % ON when heating is ON.
• Controlled to maintain the Duct Static Pressure
setpoint when cooling is ON.
• ON and controlled for heating or cooling when
the Thermostat G output is ON.
• Ramped up to its operation condition using
its variable output control when turned ON.
• OFF when heating or cooling is OFF and oc-
cupancy is UNOCCUPIED.
• An occupancy input is provided by the Ther-
mostat or Space Sensor.
• For Economizer Operation, the Economizer
Installed parameter must be ON and the Econo-
mizer Enable parameter must be ON. The econ-
omizer is:
• Closed for all unoccupied heating.
• At the minimum position for occupied heat-
ing.
• At minimum for occupied cooling when econ-
omizer is not available.
• Closed for unoccupied cooling when econo-
mizer is not available.
• At the economizer algorithm determined po-
sition for cooling with economizer available.
Unoccupied Heating With A Thermostat
The heating control is as described for “Occupied
Heating With A Thermostat” and the general operating
conditions.
Occupied Cooling With A Thermostat
• The thermostat Y1 and Y2 outputs control SAT to:
• Y1 = OFF, Y2 = OFF – No cooling
• Y1 = ON, Y2 = OFF - Cooling to SAT setpoint
VAV High Temperature Setpoint for Cooling
• Y1 = ON, Y2 = ON - Cooling to SAT setpoint
VAV Low Temperature Setpoint for Cooling
• Y1 = OFF, Y2 = ON - Cooling to SAT setpoint
VAV Low Temperature Setpoint for Cooling
Unoccupied Cooling With A Thermostat
The cooling control is as described for Occupied
Cooling With A Thermostat and the general operating
conditions.
Occupied Heating With A Space Sensor
• The programmable parameter VAV Operation with
Thermostat must be set to OFF and Space Sensor
signal must be reliable.
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