243
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
29
SECTION 29 - HEAD PRESSURE CONTROL
(SOFTWARE VERSION C.OPT.01.21.307 AND LATER)
YK chillers are capable of operation within a wide
range of condenser water temperatures. However, a
minimum condenser water temperature, as specified
in the Engineering Guide, is required to maintain suf-
ficient pressure differential (head) between the con-
denser and evaporator for proper oil and refrigerant
management in the chiller.
Should colder condenser water temperatures be antici-
pated at the cooling source, a field mounted facility
control means may be provided to ensure adequate head
pressure exists. The preferred means would be a cool-
ing tower bypass circuit that maintains a constant flow
rate through the condenser, since this would maintain
adequate tube velocity in the condenser, while regulat-
ing the return cooling water to the condenser. However,
a two-way condenser water throttling valve, a variable
speed cooling tower pump, or tower fan control circuit
might also be employed.
The head pressure control function provides an ana-
log output control signal from the OptiView Control
Center that responds to the programmed Head Pres-
sure (Condenser Pressure minus Evaporator Pressure)
setpoint. The output is direct acting (as the Head Pres-
sure increases above the setpoint, the valve is driven
more open to provide less tower bypass or more flow
through the condenser).
If the chiller is equipped for Head Pressure Control,
the feature must be ENABLED on the SETUP Screen
using the Head Pressure Control setpoint. Otherwise it
must be DISABLED. Once enabled, the HEAD PRES-
SURE CONTROL Screen is available from the CON-
DENSER Screen. All of the Head Pressure Control pa-
rameters are displayed on this screen. If Heat Recovery
is also enabled, the Head Pressure parameters appear
on the HEAT RECOVERY Screen (there is no separate
HEAD PRESSURE CONTROL Screen in this con-
figuration).
The Head Pressure feature cannot be
used with the Heat Pump feature. If
HEAT PUMP Duty is enabled, Head
Pressure will be disabled and locked.
INPUTS/OUTPUTS
The I/O used for Head Pressure Control feature is:
• Evaporator Transducer
• Condenser Transducer
• Head Pressure Control Valve output (0 to 10 VDC
or 4 to 20mA)
FIGURE 95 -
HEAD PRESSURE CONTROL BLOCK DIAGRAM
MICROBOARD
031-02430-000
031-02430-001
I/O
BOARD
031-02895-000
EVAPORATOR
TRANSDUCER
CONDENSER
TRANSDUCER
HEAD PRESSURE
CONTROL VALVE
0-10VDC or 4-20mA
RS-485
COM 3
E
VA
P
P
R
E
S
S
U
R
E
C
O
N
D
P
R
E
S
S
U
R
E
J12
2
3
J8
18 21
J9
4/12
3/11
(-)
(+)
TB2
VALVE
POSITIONING
SERIAL
COMMS
2
3
AO2
GND
LD14237
