Johnson Controls 100 Series User Manual

JOHNSON CONTROLS
109
SECTION 5 – SEQUENCE OF OPERATION
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
5
Occ Cooling with Bypass
• When in the Occ Cooling with Bypass mode,
the IPU board controls mechanical cooling to
the active evaporator air temperature (EAT)
setpoint and the return air bypass damper is
controlled to the active mixed SAT setpoint.
• When the current RAT is greater than the
active RAT setpoint plus 0.5°F and the cur-
rent RAT greater than the current mixed SAT
setpoint plus the return air diff setpoint, then
unit enters/remains in Occ Cooling with By-
pass mode.
• For the most part, when mechanical cooling
is operating on a FlexSys configured unit,
the current operating mode is Occ Cooling
with Bypass.
Active Evaporator Air Temperature Setpoint
• When in the Occ Cooling with Bypass mode,
the IPU board stages compressors ON/OFF
trying to achieve and maintain the active
EAT setpoint.
• There are two different EAT setpoints the
IPU board can choose from when in Occ
Cooling with Bypass mode.
1. EAT high setpoint: This setpoint is used
when either of the following are true:
• Return air humidity value is not
valid.
• Return air enthalpy is less than the
reset enthalpy setpoint.
2. EAT low setpoint: This setpoint is used
when either of the following are true:
• Return air enthalpy is greater than
the reset enthalpy setpoint.
• Underfloor slab dewpoint is greater
than the underfloor slab temperature
minus 2.0°F for 120 seconds (only
applicable if dewpoint reset is user
enabled).
Return Air Bypass Damper
• A FlexSys configured unit must have a re-
turn air bypass duct and damper installed for
proper operation.
• The return air bypass should be sized for no
more than 40% of the total return air.
• Johnson Controls offers a specially designed
curb for FlexSys configured units that incor-
porate the return air bypass duct and damper.
• The return air bypass damper allows warm
return air to mix with the conditioned air
leaving the evaporator coil.
• The operation of the bypass damper is very
slow and the logic that drives the damper is
quite complicated.
• When the unit is in normal operation, it could
take up to 30 minutes for the bypass damper to
go from 0–40%.
• If the unit is operating properly and the tem-
peratures are in the proper range, the damper
probably never drives to 40%.
• The IPU board opens/closes the bypass damper
to temper the air leaving the evaporator coil try-
ing to achieve and maintain the active mixed
SAT setpoint.
• Johnson Controls engineers recommend the
mixed SAT be approximately 62.0–64.0°F.
Unoccupied Cooling
• Unocc Cooling operates the same as Unocc Cool-
ing for a VAV congured unit.
• The return air bypass damper remains closed.
• Mechanical cooling and/or economizer operation
is controlled to the active mixed SAT setpoint.

Johnson Controls 100 Series Specifications

General

Brand	Johnson Controls
Model	100 Series
Category	Air Conditioner
Language	English