Chilled liquid control settings
Temperature control setpoint
The temperature to which the chiller will control the chilled fluid leaving the evaporator must be set
by the Operator. The way it is selected depends whether the Operator wants this value set locally or
modulated by a remote input.
Table 4: Temperature setpoint
Control source Leaving chilled liquid temperature setpoint
Local
Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel. It
is programmable over the range of 38.0°F to 70.0°F (water) or 10.0°F to 70.0°F
(brine). If Smart Freeze (see previous) is enabled, the range is 36.0°F to 70.0°F
(water). The default is 45 °F.
ISN (BAS)
Remote Leaving Chilled Liquid Temperature Setpoint value sent over
communications. The setpoint entered from the panel is ignored. If nothing is
written to the address, the default is 45 °F.
Analog Remote
Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel plus
the temperature offset defined by the remote analog input signal. A remote
device can provide an analog signal (0 mA to 20 mA, 4 mA to 20 mA, 0 VDC to 10
VDC or 2 VDC to 10VDC) that creates the temperature offset in Analog Remote
mode. The span of the offset may be defined as 10ºF, 20ºF, 30ºF, or 40ºF using
the Local Leaving Chilled Liquid Temperature Range setting from the panel. For
example, if this Range Setpoint is programmed for 10°F and the Local Leaving
Chilled Liquid Temperature Setpoint is 45°F, then the remote device can set the
Leaving Chilled Liquid Temperature setpoint over the range 45.0ºF to 55.0°F as its
voltage or current changes from minimum to maximum.
Digital Remote
Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel plus
the temperature offset defined by the remote pulse width signal. A remote device
can provide a Pulse Width Modulation (PWM) signal in Digital Remote mode that
creates the temperature offset in Digital Remote mode. The span of the offset
may be defined as 10ºF, 20ºF, 30ºF, or 40ºF using the Local Leaving Chilled Liquid
Temperature Range setting from the panel. For example, if this Range Setpoint is
programmed for 10°F and the Local Leaving Chilled Liquid Temperature Setpoint
is 45°F, then the remote device can set the Leaving Chilled Liquid Temperature
setpoint over the range 45.0ºF to 55.0°F as its pulse duration changes from
minimum to maximum. The PWM input is in the form of a 1 to 11 second relay
contact closure that applies 115 VAC to the I/O Board TB4- 19 for 1 to 11 seconds.
A contact closure time (pulse width) of 1 second produces a 0°F offset. An 11
second closure produces the maximum offset. The relay contacts should close
for 1 to 11 seconds at least once every 30 minutes to maintain the setpoint to the
desired value. If a 1 to 11 second closure is not received within 30 minutes of the
last closure, the offset is defaulted to zero. A closure is only accepted at rates not
to exceed once every 70 seconds. Offset (°F) = (pulse width in seconds – 1)( Local
Leaving Chilled Liquid Temperature Range) divided by 10.
Regardless of which method is used to select the desired Leaving Chilled Liquid Temperature
(LCHLT), the chiller controls to its own Active LCHLT Setpoint. The Active Setpoint is a target to the
programmed setpoint. When the chiller is not running, the Active Setpoint is set to Entering Chilled
Liquid Temperature minus a programmable offset (default 5°F), but not adjusted to less than the
programmed LCHLT setpoint. When the compressor motor starts, the Active LCHLT Setpoint is
21
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