Table 10: Temperature setpoint
Control source LCHLT setpoint
Local
Local cooling setpoint is entered from the panel. It is programmable over the range of 50°F to 80°F (10°C to 26.7°C) for water or brine
applications. The default is 70°F (21.1°C).
BAS
Remote cooling setpoint value sent over communications. The local setpoint entered from the panel is ignored. It is limited to the same
minimum and maximum allowable temperatures as the local setpoint. If nothing is written to the address, the default is 70°F (21.1°C).
0 V to 10 V or 4mA to 20
mA
Remote Cooling setpoint set by an analog input signal from the BAS. A remote device can provide an analog signal of 4 mA to 20 mA or 0
VDC to 10 VDC to a microboard input connection.
A setpoint range (minimum 0° F to maximum 200°F) is user defined and allows for complete flexibility for the BAS controls. The remote
signal varies linearly between the defined range. The local setpoint entered from the panel is ignored. It is limited to the same minimum
and maximum allowable temperatures as the local setpoint.
For example, if the remote setpoint minimum is set to 50°F (10.0°C) and the remote setpoint maximum is set to 70°F (21.1°C), then a
signal of 0VDC commands a 50°F (10.0°C) setpoint and a 10 VDC signal commands a 70°F (21.1°C) setpoint. A signal of 5 VDC would
command a 60°F (15.6°C) setpoint.
PWM
Remote cooling setpoint set by a digital input signal from the BAS. A remote device can provide a pulse-width modulation input in the
form of a 1 second to 11 seconds relay contact closure that applies the provided 115 VAC to the I/O board input.
The setpoint varies linearly from the remote setpoint minimum value to the remote setpoint maximum value as the relay contact closure
time changes from 1 s to 11 s. The local setpoint entered from the panel is ignored. It is limited to the same minimum and maximum
allowable temperatures as the local setpoint.
For example, if the remote setpoint minimum is set to 50°F (10.0°C) and the remote setpoint maximum is set to 70°F (21.1°C), then a
signal pulse duration of 1 s commands a 50°F (10.0°C) setpoint and a signal pulse duration of 11 s commands a 70°F (21.1°C) setpoint. A
signal pulse duration of 6 s would command a 60°F (15.6°C) setpoint.
The relay contacts must close for 1 s to 11 s at least once every 30 min to maintain the setpoint to the preferred value. If a 1 s to 11 s
closure is not received within 30 min of the last closure, the setpoint defaults to the local setpoint. A closure is only accepted at rates not
to exceed once every 70 s.
Regardless of which method is used to select the preferred 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 (-15°C), but not adjusted to less than the programmed LCHLT
setpoint. When the compressor motor starts, the active LCHLT setpoint is ramped from this value
to the programmed LCHLT setpoint at the programmable LCHLT setpoint ramp rate, default 0.1°F/
s (-17.7°C/s). This keeps the chiller from undershooting the setpoint excessively during pulldown.
Any time the programmed setpoint is changed during operation, the active setpoint is ramped to
the new value at this rate.
Automatic temperature shutdown
The LCHLT cycling offset, shutdown setting on the panel can be programed to set the temperature
below the LCHLT setpoint at which the chiller automatically cycles off when the load is less than the
chiller minimum capability. This setting defines the temperature offset below the LCHLT setpoint
where shutdown is expected. It is programmable over a range of 1°F to 64°F (-17.2°C to 17.8°C).
However, the actual shutdown temperature is never calculated to lower than 36°F (2.2°C) for water,
34°F (1.1°C) for water with smart freeze enabled, or 6°F (-14.4°C) for brine. Anytime the LCHLT
setpoint is decreased, the shutdown threshold decreases to the new LCHLT active setpoint minus
offset at a rate equal to the programmed LCHLT setpoint ramp rate. Anytime the LCHLT setpoint
is increased, the shutdown threshold increases to the new LCHLT active setpoint minus offset at a
rate equal to half the programmed LCHLT setpoint ramp rate. This provides time for the chiller to
change temperature without shutting down first.
Automatic temperature restart
The LCHLT cycling offset, restart setting on the panel can be programed to set the temperature
above the LCHLT setpoint at which the chiller automatically restarts after a low LCHLT shutdown,
as described previously. This setting defines the temperature offset above the LCHLT setpoint
where automatic restart is expected. It is programmable over a range of 0°F to 70°F (-17.8°C to
21.1°C). However, the restart temperature is never calculated above 80°F (26.7°C). You can use this
setpoint to reduce chiller cycling by delaying the chiller restart until the cooling load has increased
sufficiently.
33YVAM with OptiView Control Center
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