System Start-Up - Trane CSRA025FAF0 Installation Operation & Maintenance

System Start-Up

Sequence of Operation
Chiller Control for Comfort Applications
The CGM controls the leaving solution temperature (LST) to within an
adjustable setpoint using deadband control. The CGM monitors the LST
sensor and determines how far away the temperature is from the leaving
solution setpoint (LSS). The compressors are staged On/Off depending on
where the LST is within the control deadband.
Deadband Calculation
The rate at which capacity stages are added or subtracted is determined by
a control algorithm The CGM control deadband for comfort applications is a
calculated value based upon the control response setpoint, the difference
between LSS and LST, the number of capacity steps, the design delta
temperature (DDT) of the system, and the number of capacity steps. The
minimum comfort deadband is 1 degree F. The maximum comfort deadband
above or below the LSS is 10°F for a two stage unit and 5°F for a 4 stage
unit.
When the LST is inside the control deadband, the calculation is cleared and
no response is initiated. When the LST is outside the deadband and the
calculated control algorithm value equals 1, a capacity add command is
initiated. Conversely, when the value of the control algorithm equals -1, a
capacity subtract command is initiated. Once a capacity add or subtract
command is given and a change in the compressor staging has been
detected, the value of the control algorithm is reset to 0.
Chiller Freeze Protection
The CGM prevents evaporator fluid from freezing by utilizing two separate
algorithms. One is the evaporator limit control algorithm which stages
compressors "Off" if violated and the other is the evaporator freeze
protection algorithm which activates auto/manual diagnostics if violated. The
freeze protection function will always operate as long as the unit is in the
Auto mode for both normal cooling applications and/or ice building modes. A
manual reset diagnostic will occur if all compressors are shut off due to a
freeze protection violation.
The evaporator limit control integrator (ELCI) algorithm calculates a value
based upon the low leaving solution temperature cutout setpoint and the
leaving solution temperature. When the value for ELCI drops below -1, the
unit control will reduce the chiller capacity by staging down and/or inhibiting
a compressor from operation. After each capacity subtract command from
the capacity control algorithm is issued, ELCI is increased by 1 and retained.
The ELCI is set to 0 any time the leaving solution temperature is greater than
or equal to the low leaving solution temperature cutout (LLSC) + 3°F.
Compressors will be prevented from operating until the leaving solution
temperature (LST) is 4°F above the LLSC.
If Pumpdown is enabled and a subtract command is issued, the circuit will
be allow to pumpdown.
54 CSRA-SVX02A-EN