JOHNSON CONTROLS
103
SECTION 5 – SEQUENCE OF OPERATION
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
5
VARIABLE AIR VOLUME (VAV) MODE
OPERATION
For proper operation of the supply fan
a delay may need to be added to the unit
to allow for the VAV boxes to fully open
before the supply fan starts. This can be
done through the BAS by delaying the
occupied command.
For proper operation the VAV box mini-
mum positions must be set to equal or
exceed the minimum VAV ow of the unit.
If the minimum VAV ow set points are
not greater than the minimum airow for
the unit, nuisance supply fan lockouts
could occur.
The “CURRENT OPER MODE,” OCCUPIED or UN-
OCCUPIED, is a derived value and is established in
four ways:
• Placing the ON / AUTO / OFF toggle switch,
located below the keypad and display, from the
OFF to ON position. This closes a circuit between
“24VAC” and “OCC” on the CTB1 terminal block
• Placing the ON / AUTO / OFF toggle switch from
the OFF to AUTO position and supplying a digital
input, ON occupied / ON / AUTO / OFF unoccu-
pied. The digital input is made through a connec-
tion between “24VAC” and “OCC” on the CTB1
terminal block
• Placing the ON / AUTO / OFF toggle switch from
the ON / AUTO / OFF to AUTO position and
supplying a serial input “OCCUPANCY COM-
MAND.” This would usually originate from a BAS
• Placing the ON / AUTO / OFF toggle switch,
from the ON / AUTO / OFF to AUTO position
and using the Internal Time clock “OCCUPAN-
CY SCHEDULE.” Use the PROGRAM key on
the User Interface turn ON and OFF the Internal
Time clock. Programme the occupied / unoccu-
pied schedule through the SCHEDULE key of the
User Interface
Variable Air Volume (VAV) Supply Fan
The Supply Fan is turned ON if the Supply Fan is OFF
for at least 60 seconds and one of the following condi-
tions apply:
• The “CURRENT OPER MODE” is set to OCCU-
PIED
• Or the unit is in the MORNING WARMUP mode
• Or the UNIT MODE is UNOCCUPIED HEAT-
ING OR UNOCCUPIED COOLING
The Supply Fan is turned OFF if all the following con-
ditions are met:
• The Supply Fan has is ON for at least 60 seconds
• The unit is in the UNOCCUPIED STANDBY
mode
• The INACTIVE HEATING TIME is greater than
or equal to 60 seconds
• The INACTIVE COOLING TIME is greater than
or equal to 60 seconds
• The Supply Air Temp is less than or equal to
85.0°F
The Unit Controller monitors the operation of the Sup-
ply Fan by checking the status of a digital input from
an air proving switch. After 60 seconds of operation,
the control looks for a high state (24 volt input) from
the air proving switch circuit at terminal block J13, pin
2 of the Unit Controller. It examines the current status
for 10 seconds. If the input does not go to a high state
during this time frame, the Unit Controller sets a SUP-
PLY FAN LOCKOUT and shut down all unit system
operation.
The Unit Controller uses a proportional-integral con-
trol algorithm to maintain the DUCT STATIC PRES-
SURE by varying the speed of the supply fan. As the
pressure goes up, the speed goes down, and in turn
as the duct pressure goes down, the fan speeds up to
maintain a DUCT STATIC PRESSURE.
This unit also has a SUPPLY FAN LIMIT LOCKOUT.
UNIT TYPE is set to VARIABLE AIR VOLUME or
FLEXSYS and the SUPPLY FAN VFD BYPASS is set
to USER DISABLED. When the SUPPLY FAN VFD
SPEED in parentage is < SUPPLY FAN LOCKOUT
LIMIT, the supply fan stays in operation. Otherwise,
LOCKOUT-SUPPLY FAN goes into effect when SUP-
PLY FAN OUTPUT shows ON and SUPPLY FAN
STATUS is STOPPED for 30 seconds. LOCKOUT-
SUPPLY FAN is cleared when the set conditions are
no longer present if the unit is shut down.
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