JOHNSON CONTROLS
108
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
SECTION 5 – SEQUENCE OF OPERATION
• When a FlexSys unit enters an Active Occ Cool-
ing mode, it always starts in Occ Cooling without
Bypass for the îš¿rst 30 seconds.
• After this 30 seconds has elapsed, the IPU board
decides which Occ Cooling mode to be in.
• Unocc Cooling mode is the same as a VAV cong-
ured unit. The return air bypass damper remains
closed.
Occupied Cooling
Occ Cooling without Bypass
• When in the Occ Cooling without Bypass
mode, the IPU board controls mechanical
cooling or economizer operation to the ac-
tive mixed SAT setpoint.
• When the economizer is active, the unit re-
mains in the Occ Cooling without Bypass
mode.
• When the current RAT is greater than the
active RAT cooling setpoint plus 0.5°F but
the current RAT is less than the mixed SAT
setpoint plus the return air diff setpoint, the
unit remains in the Occ Cooling without By-
pass mode.
• When in Occ Cooling without Bypass, the re-
turn air bypass damper remains fully closed.
LD28133
FIGURE 57 - FLEXSYS — UNOCCUPIED
Fan Operation
• The same as a VAV congured unit, the supply fan
is controlled by a VFD.
• The VFD controls the speed of the supply fan up/
down to achieve and maintain the active duct stat-
ic setpoint.
• Due to the nature of a UFAD system, typical duct
static setpoints may be much lower than a normal
VAV system.
• The same as a VAV configured unit, the supply
fan is on whenever the unit is in the Occ mode,
and cycles ON/OFF in the Unocc mode with a de-
mand for cooling or heating.
Cooling
• The sequence of operation for cooling on a Flex-
Sys unit differs from a traditional VAV system.
• A FlexSys unit has two different Occ Cooling
modes:
• Occupied Cooling without Bypass
• Occupied Cooling with Bypass
• The IPU board has internal logic it uses to deter-
mine which Occ Cooling mode to use.
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