JOHNSON CONTROLS
127
SECTION 5 – SEQUENCE OF OPERATION
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
5
Condenser Enabled / Waterside
Economizer Disabled Manually
Under this mode of operation, the unit has an actuator
driven water valve that controls the flow of condenser
water through the water condenser, but this disables the
waterside economizer valve through the User Interface
on the unit.
The following parameters must be programmed into
the Unit Controller through the User Interface to
achieve this operation:
• OPTIONS key, CONDENSER subsection:
• “COND VALVES INSTALLED” should be
set to COND ONLY
• “CONDENSER TYPE” should be set to WA-
TER COOLED
• OPTIONS key, ECONOMIZER subsection:
• “ECONO INSTALLED” should be set to
WATERSIDE
• “ECONO METHOD TO USE” should be set
to WATERSIDE
• PROGRAM key, CONDENSER subsection:
• “COND WATER CONTROL” should be set
to ENABLED
• “ECONOMIZER CONTROL” should be set
to ENABLED
• SETPOINTS key, CONDENSER subsection:
•
“COND VALVE MIN POS” (default is 30%)
• “DISCHARGE PRESSURE SP MIN”
(default is 225 PSIG)
• “DISCHARGE PRESSURE SP MAX”
(default is 400 PSIG)
All waterside economizers have a fac-
tory installed freezestat that must be set
as ENABLED under the OPTIONS key,
UNIT DATA subsection. See Freezestat
Sequence of Operation
The condenser actuator driven valve is inverse acting.
When the voltage output to the valve is 10VDC, the
valve is closed. When the voltage output to the valve is
2VDC or less, the valve is wide open. The CONDENS-
ER WATER VALVE analog output is located at J15-8.
Analog Outputs to the Valves
No Cooling Needed:
The COND WATER VALVE
analog output is 10VDC (0%) when the unit's STA
-
TUS is “CURRENT OPER MODE” UNOCCUPIED
STANDBY or OCCUPIED STANDBY. There is no
call for cooling at this moment.
Cooling Becomes Active:
The COND WATER
VALVE analog output is 2VDC (100%) when the unit's
STATUS is “CURRENT OPER MODE” UNOCCU-
PIED or OCCUPIED COOLING and no compressors
are ON at this moment.
When one of the compressors come ON, the COND
WATER VALVE analog output is controlled by the
CONDENSER PRESSURE PI OUTPUT.
The CONDENSER PRESSURE PI OUTPUT is based
on the lowest of the “AVG PRESS – DISCHARGE
A” when active for 60 seconds, “COMP SYSTEM B
DISCHARGE PRESSURE” when active for 60 sec-
onds, and any additional compressor discharge pres-
sures when active for 60 seconds. The Unit Controller
tries to maintain the pressure to the programmed “DIS-
CHARGE PRESSURE SETPOINT.”
Some of the compressors used in these units employ in-
ternal line break protection. The Unit Controller could
think that a compressor is active when it is physically
offline. This causes the Unit Controller to calculate a
DISCHARGE PRESSURE MINIMUM demand based
on a compressor that is not operating, which could
result in a discharge high pressure fault. To prevent
nuisance discharge high pressure faults, the Unit Con-
troller also compares the maximum discharge pressure
of the active compressor systems to the programmed
"DISCHARGE PRESSURE SP MAX." The default
value is factory set to 400 PSIG. The Unit Controller
generates a DISCHARGE PRESSURE MAXIMUM
demand.
The Unit Controller uses the greater of the DIS-
CHARGE PRESSURE MINIMUM and the DIS-
CHARGE PRESSURE MAXIMUM demands for the
control of the condenser water valve.
Waterside Economizer Coil Flush Cycle
The controller can be programmed to flush the water
economizer coil daily to minimize contamination and
dirt buildup in the waterside economizer coil.