JOHNSON CONTROLS
121
SECTION 5 – SEQUENCE OF OPERATION
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
5
compares the maximum discharge pressure of the ac-
tive compressor systems to the programmed "DIS-
CHARGE 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.
100%
(2 VDC)
0%
(10 VDC)
COND VALVE
MIN POS
COND WATER
VALVE AO
CONDENSER PRESSURE
PI OUTPUT
100%
0%
LD21632
FIGURE 74 -
COND WATER VALVE VS. CONDENS-
ER PRESSURE PI OUTPUT
The following two settings are based on the building
and system design. These two systems pertain to the
building operation, and the unit can be programmed to
work with these two systems.
•
Variable Flow:
Condenser water pressure and
gallons per minute (GPM) are varied by a variable
speed drive (VSD) on the system pump.
•
Constant Flow:
The condenser water system
maintains a set pressure and GPM based on the
pumps running at full speed.
CONDENSER WATER SYSTEM is Variable Flow
The COND WATER VALVE analog output is closed
(0%) when all three of the following conditions are
present:
• “CURRENT OPER MODE” is in STANDBY and
UNOCCUPIED COOLING, UNOCC COOL-
ING LOW, UNOCC COOLING HIGH, OCCU-
PIED COOLING, OCC COOLING LOW, OCC
COOLING HIGH, OCC COOLING W/ BYP,
OCC COOL W/O BYP, or COMFORT VENT
COOLING
• Compressors are OFF for at least 60 seconds
• COND WATER SYSTEM is Variable Flow
CONDENSER WATER SYSTEM is Constant Flow
The COND WATER VALVE analog output is open
(100%) when all three of the following conditions are
present:
• “CURRENT OPER MODE” is in STANDBY and
UNOCCUPIED COOLING, UNOCC COOLING
LOW, UNOCC COOLING HIGH, OCCUPIED
COOLING, OCC COOLING LOW, OCC COOL-
ING HIGH, OCC COOLING W/ BYP, OCC COOL
W/O BYP, or COMFORT VENT COOLING
• Compressors have been OFF for at least 60 sec-
onds
• COND WATER SYSTEM is Constant Flow
The CONDENSER PRESSURE PI is enabled and
CONDENSER PRESSURE PI OUTPUT coupled to the
condenser valve output (COND WATER VALVE) when
both of the following conditions are satisfied:
• “COND WATER CONTROL” is USER ENABLED
• At least one compressor has been ON for at least
60 seconds
The COND WATER VALVE analog output is opened
100% in all other cases.
Condenser Valve with Bypass Valve
Under this mode of operation, the unit has an actuator
driven water valve that controls the flow of condenser
water through the water condenser and a bypass water
valve. This is two separate valves. Verify that the unit
is not using a waterside economizer for operation since
that option also has two valves.
WATER-COOLED
CONDENSER
WATER
SUPPLY
WATER
RETURN
Condenser Valve with Bypass Valve
CONDENSER
VALVE
M
M
BYPASS
VALVE
LD21633
FIGURE 75 -
CONDENSER OPERATION AND PIPING
DIAGRAM W/ CONDENSER AND BYPASS VALVES