Trane IntelliPak CG-SVX02B-EN, Installation & Operation Manual

Page: 42 / 64

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System Start-Up
Ice Building can be terminated by:
Opening the customer provided field installed remote
device, or
Ice building stopped from ICS communications.
If at any time the unit is switched from the Ice Building
mode to normal comfort operation, the unit will transition to
ice building complete status and stage all operating com-
pressors “Off”.
Sequence of Operation
Chiller Control for Process Applications
Process applications are characterized as having fast
changes in load and these loads are not adequately con-
trolled with the same scheme used for comfort applications.
To provide better control of these dynamic loads, a Propor-
Integral “control to setpoint” (as opposed to “control
to deadband”) control strategy is used. System reliability is
inversely proportional to compressor cycle rates so reliabil-
ity is the driving factor for determining maximum cycle rate
which ultimately translates into cycle-to-cycle leaving solu-
tion temperature swings.
To provide stable capacity control, a 1 minute minimum time
between compressor starts is required. The control will de-
termine an estimate of instantaneous load based on error
from setpoint for the leaving solution temperature and cycle
the appropriate compressor stage to best match the calcu-
lated load.
Determining instantaneous error:
Error = Chiller Solution Temp - Chiller Solution Setpoint.
PI Control Calculation:
The CGM calculates the Load Value by applying PI calcula-
tions to the instantaneous error value. The Load Value con-
sists of an integer part and a fractional part. The integer
part represents which compressor stages are locked “On”
and the fractional part represents the duty cycle required for
the next higher compressor stage. For a 4 compressor unit,
the Load Value will range from 0.0 to 4.0. For a 2 compres-
sor unit, the Load Value will range from 0.0 to 2.0.
Duty Cycle Calculations calculate the duty cycle based on
the calculated Load Value Fraction:
On Time
Seconds = 3600 / 4 X Max Cycle Rate X (1-Load Value
Fraction)
Off Time
Seconds = 3600 / 4 X Max Cycle Rate X Load Value
Fraction
Where Load Value Fraction = Fractional part of the calcu-
lated Load Value.
Sequence of Operation
Leaving Solution Reset (LSR)
Leaving Solution Reset (LSR) refers to the process of ad-
justing the Leaving Solution Setpoint (LSS) based on an ex-
ternal temperature.
When the optional Leaving Solution Reset (LSR) feature is
used, the CGM will automatically adjust the LSS in re-
sponse to a temperature change from one of three different
temperature sensor:
1. Zone Temperature sensor
2. Outside Air Temperature sensor
3. Entering Solution Temperature sensor.
The reset temperature value (Start Temperature), to start
resetting the Leaving Solution Setpoint (LSS) and the maxi-
mum amount of reset to be applied to the LSS is program-
mable through the Human Interface. The reset amount ap-
plied to the LSS is a linear calculation between the Start
Temperature and the End Temperature. After the reset
amount has been calculated, it is added to the Leaving So-
lution Setpoint to create the Leaving Solution Reset
Setpoint. If the solution temperature is above the selected
Start Temperature, the reset amount is zero. If the solution
temperature is below the End Temp, the maximum amount
of reset is applied. For reset type ‘None’, the amount of re-
set is zero. Refer to the appropriate reset type in Table 5-1
for reset schedules.