14
ADJUSTING PID ROUTINES — The 30GX and 30HXC
head pressure control routines use PID (proportional integral
derivative) loops to maintain a user-configurable head pressure
set point. Gain default values are located in the Service func-
tion. See page 32. The current values can be read under
from the HSIO. The control calculates a new fan
speed (30GX) or water valve position (30HXC) every 5 sec-
onds based on these gain values and an error term equal to sat-
urated condensing temperature minus head pressure set point.
If the control routine is not responding fast enough to large
changes (circuit starting, for example), increase the propor-
tional term.
When the routine is making too great a change to valve po-
sition or fan speed, decrease the proportional term. To mini-
mize hunting, keep the integral term positive and as low as pos-
sible. This value is used to control “droop,” which is common
in master/submaster control schemes. The default for the deriv-
ative term is zero. The value should not need to be changed.
Cooler and Condenser (30HXC) Pump Con-
trol —
The 30GX and 30HX chillers can be configured for
cooler and condenser (30HXC) pump control. Inputs for a
cooler flow switch or interlock and condenser flow switch are
also provided.
COOLER PUMP CONTROL — Proper configuration of the
cooler pump control and cooler pump interlock is required to
prevent possible cooler freeze-up. The cooler pump interlock
should always be enabled. This prevents the chiller from oper-
ating unless chilled water flow is detected. See page 73 of the
Field Wiring section for proper connection of the chilled water
flow switch and cooler pump interlock.
The factory default setting for cooler pump control is “0”
(not controlled). It is recommended for 30GX packaged air-
cooled chillers that the cooler pump control be utilized unless
the chilled water pump runs continuously or the chilled water
system contains a suitable anti-freeze solution. The cooler
pump relay is energized when the chiller enters an occupied
mode. In the event a freeze protection alarm is generated the
cooler pump relay is also energized. If the cooler heater is
being used and has been on for more than 15 minutes during
saturated suction freeze protection, the cooler pump relay is
energized.
When the cooler pump control is set to “0” and the cooler
pump interlock is set to “1” an alarm 53 will be generated if
flow is not proven within one minute after the unit is enabled
and in an occupied mode.
DECREASE
CURRENT FAN
STAGE BY ONE
NO
NO
YES
IS SCT GREATER
THAN HEAD
PRESSURE SET
POINT PLUS 15
°
F
(8.3
°
C)?
INCREASE
CURRENT FAN
STAGE BY ONE
YES
READ CIRCUIT
SATURATED
CONDENSING
TEMPERATURE
AND CURRENT
FAN STAGE
NO
INCREASE
CURRENT FAN
STAGE BY ONE
YES
CALCULATE NEW
PID VALUE. DOES
OUTPUT REQUIRE
MORE FANS?
OUTPUT NEW mA
SIGNAL TO
CONTROLLER
DOES PID OUTPUT
REQUIRE LESS
FANS?
30GX UNITS — MOTORMASTER III CONTROL NOT INSTALLED
LEGEND
SCT — Saturated Condensing Temperature
30GX UNITS — MOTORMASTER III CONTROL INSTALLED
Fig. 6B — 30GX Head Pressure Control Without Motormaster III Control
Fig. 6A — 30GX Head Pressure Control Without Motormaster
®
III Control