Trane CVGF-SVU02B-E4 Operation And Maintenance Manual page 66

Differential to Start or Stop
The Differential to Start setpoint
is adjustable from 1 to 10°F (0.55
to 5.5°C) and the Differential to
Stop setpoint adjustable from 1
to 10°F (0.55 to 5.5°C). Both
setpoints are with respect to the
Active Chilled Water Setpoint.
When the chiller is running and
the Leaving Water Temperature
(LWT) reaches the Differential to
Stop setpoint the chiller will go
through its shutdown sequence
to Auto. Reference 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.
66
Machine Protection and
Adaptive
There are three independent
Softload setpoints:
• Capacity Control Softload Time
default is to 10 minutes and
settable from 0-120 minutes.
This setting controls the time
constant of the Filtered Chilled
Water Setpoint.
• Current Limit Control Softload
Time default is 10 minutes and
settable from 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 and settable from 20-100
percent. This setting controls
the Starting point of the
Filtered Current Limit Setpoint.
Note: TechView ™ provides
access to these three setpoints.
Minimum and Maximum
Capacity Limit
A Minimum Capacity can be set
to limit the unloading ability of
the compressor forcing
differential 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 using TechView
CVGF-SVU02B-E4
™ .