Operation

Inlet Rack Temperature Control

The Liebert iCOM Optimized Aisle control monitors the inlet temperature to the racks using up to 20 rack temperature sensors that are connected to a Liebert iCOM control. These inlet rack temperature sensors are used to control the air flow (fan speed) of each unit. The air flow is increased when the inlet rack sensors detect a temperature higher than the setpoint and will decrease air flow when the head load decreases or changes to the application are modified (eg., Containment).

Additional Details of Rack Temperature Operation

Refer to Application and Configuration of Rack Sensors on page 81 for rack sensor setup details.

• The cooling unit’s fan speed is determined based on the amount of deviation from temperature setpoint (Proportional) and the length of time the actual temperature has deviated from temperature setpoint (Integral)

• The fan speed control takes into account the actual temperature as it compares to the

temperature setpoint and will modify how fast the fans can change speed to avoid overshooting the setpoint.

In addition to the speed filters, the fan speed also has programmed independent acceleration and deceleration rates

These control tuning parameters allow the fans to speed up quickly to match rapid heat load changes and react to containment doors being opened and closed while still providing stable control when the application returns to steady state operation.

Temperature Compensation

Temperature compensation links between the cold aisle temperatures, cooling capacity and air flow. Changes that could invoke temperature compensation would be the removal of floor tiles in non-cold aisle areas, incorrect supply temperature setpoint, unit failure in another zone or heat load changes greater than expected heat load changes in rack equipment. As a further protection, the temperature compensation routine also ties into the cascade /standby operation when Teamwork Mode 3 is selected.

There are three selectable compensation routines to choose from: Return, Supply or Return + Supply.

Return Compensation: This temperature compensation monitors the return air condition and

automatically adjusts the supply air setpoint if return temperatures become too cold. Return compensation can be enabled in all fan and temperature control sensor configurations, with the exception of fan and cooling set for return air control (Enable Return Compensation falls back to No). With return air compensation enabled, S103 “Temperature Setpoint” remains unchanged as long as the air temperature is above S114 “Return Compensation Setpoint.”

If the return air temperature falls below S114 “Return Compensation Setpoint,” S103 “Temperature Setpoint” will be increased. The calculated compensation setpoint is displayed as the left hand value (Act) of line S103 (see Figure 49). Return compensation is also indicated from the unit view as shown in Figure 50.

Figure 49 Return Compensation Setpoint in Service Menu

Figure 50 Return Compensation in Unit View

Calculated Return Compensation Setpoint Return Compensation in Unit View

Figure 51 Return Compensation control band

The return compensation setpoint will proportionally increase as the return temperature deviates below S114 “Return Compensation Setpoint.” The compensation proportional band is set on line S115. The compensating proportional band defines the maximum value the air temperature setpoint will increase during return compensation. See Figure 51.

Figure 52 Return Compensation setpoint deviation

Supply Compensation: Supply temperature compensation allows units to automatically adjust the

supply air temperature setpoint when the unit has reached its maximum airflow of 100% and the cold aisle temperature remains above the cold aisle setpoint. In this situation, the temperature

compensation feature will proportionally decrease the supply air setpoint until the Inlet rack temperature reaches the setpoint.

-100%

S115 Return Compensation Band

S114 Return Compensation Setpoint

S115 Return Compensation Value _{Temperature Setpoint} (Sensor set to either Supply Sensor

or Remote Sensor ) New air temperature

setpoint modified by compensation Return Compensation Proportional Band Return Compensation Maximum Value

Figure 53 Supply compensation

When supply air compensation has been invoked, it will be indicated on the unit view by a small downward-pointing arrow. See Figure 54.

Figure 54 Supply Compensation in Unit View

During normal operation, as the rack temperature increases above the fan temperature setpoint, the fan speed will increase until it reaches 100% speed. 100% fan speed is achieved once the controlling temperature reaches a value equal to 100% of the fan control band, or S116 Fan Setpoint + 1/2(S150 Fan Deadband) + 1/2(S149 Fan Temp Prop Band).

Fan

Speed

100%

Lowe

r Sup

ply

How many degrees the supply temperature will be lowered while supply compensation is invoked depends on how many degrees the fan controlling temperature has exceeded the control band compared to S116 Supply Compensation Value.

Example: With a Fan Setpoint of 70ºF and Proportional band of 10ºF, 0ºF deadband, the fan

speed is 100% when the rack temperature is 75ºF. If S116 Supply Compensation value = 10ºF, the supply air temperature will lower one degree for every degree the rack temperature increases outside the fan control band. This means if the air temperature setpoint is 65ºF, and the rack temperature increase to 77ºF, the supply air temperature will lower to 63ºF.

Return + Supply Compensation: This selection provides the ability to enable both supply and

return compensation settings as described above.

Figure 55 Supply compensation

Figure 56 Temperature/humidity/static pressure control sensors in Optimized Aisle

76 78 74 73 72

100%

Compensation

50%

Compensation

Blower at 100%

of Capacity

Blower Proportional Band

Fan Speed Proportional Band 8°F (4°C)

Supply Temperature Setpoint

will be decreased by the Supply

Compensation band when the

fan speed proportional band

has doubled

After the blower reaches 100 percent and the temperature continues to increase, the supply temperature setpoint will be decreased proportionally Supply Compensation Band 8°F (4°C) Return Temperature/ Humidity Sensor Supply Temperature Sensor

Inlet Rack Sensor Static Pressure