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17InRow RC Operation and Maintenance Manual
Control the Environment
The primary function of the cooling unit is to cool air from the hot aisle and deliver it to the cold aisle at the
temperature setpoint. The control strategies employed by the cooling unit depend upon the deployment
strategy of the cooling group.
In an in-row environment, the cooling unit supplies constant-temperature supply air to the common cold aisle.
The fan speed is modulated to ensure that the desired volume of air reaches the IT equipment. The fan speed
is determined by the difference between the cooling setpoint and the maximum rack air inlet temperature.
In a HACS or RACS environment, the cooling unit neutralizes the heat accumulated in the common hot aisle
and expels it back into the surrounding environmental space while maintaining the desired temperature in the
cold aisle.
How the Cool mode works
Cool: Cooling control is varied based on configuration:
• InRow: The equipment maintains the supply air temperature setpoint by regulating the flow of chilled
water through the cooling coil. The evaporator fan speed is controlled by comparing the rack inlet
temperature to the cooling setpoint. As the rack temperature increases compared to the cooling setpoint,
the fans increase output to maintain the setpoint. As rack temperature decreases compared to the
cooling setpoint, the fans decrease output to maintain the setpoint.
• RACS/HACS: The supply air setpoint is maintained the same way as with the InRow configuration. The
fan speed is controlled by the fan speed preference setting. The fan speed can be selected based on the
temperature differential across the cooling unit. As actual supply and return temperatures deviate from
the fan speed preference setting, the fan speed increases to bring the temperature difference back down
to the setpoint or decreases fan output to increase the unit temperature differential.
Fluid Calibration Mode: Runs the cooling unit with the valve fully open and at minimum fan speed. This
special mode is typically used to balance the fluid flow in multiple units or in one unit. This mode generates a
critical alarm. The cooling unit will take some time to return to normal operation once the Fluid Calibration Mode
is turned off.
See Supply Air and Return Air on page 24 for more information.
Setpoints
Path: Main > Set Group Setpoints
A setpoint is the target value that a cooling group tries to maintain in the rack. The default setpoints are
appropriate for most cooling applications.
The setpoints for each mode must be within the following ranges:
• Cool: 18.0 – 25.0 °C (64.4 – 90.0°F)
• Supply Air: 17.0 – 23.0 °C (59.0–86.4°F)
NOTE: The Supply Air setting is defined when the cooling group is commissioned. This task is
performed by authorized personnel only.