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CVHE-SVU01E-EN
Differential to Start or Stop
The Differential to Start setpoint is
adjustable from 1 to 10°F (0.55 to
5.55°C) and the Differential to Stop
setpoint adjustable from 1 to 10°F
(0.55 to 5.55°C). Both setpoints are
with respect to the Active Chilled
Water Setpoint. When the chiller is
running and the LWT (Leaving Water
Temperature) reaches the Differential
to Stop setpoint the chiller will go
through its shutdown sequence to
AUTO. (Refer to Figure 10.)
SoftLoading
Softloading stabilizes the startup
control during the initial chiller
pulldown. Soft loading is used to
bring the building loop temperature
from its start value to the Chilled
Water or Hot Water Setpoint in a
controlled manner. Without soft
loading, the chiller controls will load
the chiller rapidly and use the full
chiller capacity to bring the loop
temperature to setpoint. Although the
start temperature of loop may have
been high, the actual system load
may be low. Thus, when the setpoint
is met the chiller must unload
quickly to the system load value. If it
is not able to unload quickly enough,
the supply water temperature will
drop below setpoint and may even
cause the chiller to cycle off. Soft
loading prevents the chiller from
going to full capacity during the
pulldown period. After the
compressor has been started, the
starting point of the filtered setpoint
is initialized to the value of the
Evaporator Leaving Water
temperature and the percent RLA.
There are three independent Softload
setpoints:
• Capacity Control Softload Time
(default to 10 minutes, 0-120
minutes) This setting controls the
time constant of the Filtered Chilled
Water Setpoint.
• Current Limit Control Softload Time
(default 10 minutes; 0-120 minutes)
This Setting controls the time
constant of the Filtered Current
Limit Setpoint.
• Current Limit Softload Starting
Percent (default is 40 percent RLA;
20-100 percent): This setting
controls the Starting point of the
Filtered Current Limit Setpoint
Service tool provides access to these
three setpoints, if it is determined
necessary to change from the
defaults.
Softloading is not active during Ice
Making or during the Ice To normal
Transition. Softloading will be
enabled after the Ice to normal
Transition timer has expired.
Softloading is not active during Free
Cooling, The softloading is active
during the transition from Free
Cooling to Powered operation.
Softloading times can be active
during Hot Gas Bypass Control
Minimum and Maximum Capacity
Limit
A Minimum Capacity can be set to
limit the unloading ability of the
compressor thus forcing differential
to stop to be reached cycling the
chillers. Minimum capacity limit will
be displayed when in this limit
mode. This indicates when the chiller
is running fully unloaded.
Similarly a maximum capacity can be
set to limit normal chilled water
temperature control, the maximum
capacity relay is energized which is a
signal used by generic BAS systems
to start another chiller.
The minimum (default at 0 percent)
and maximum (default at 100 percent)
capacity are adjustable via the service
tool.
Machine Protection
and Adaptive
Control