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Chapter 4: E2 Controller
4.4.4 Airflow/Fan Speed Control
The E2 controller treats each EC fan as a variable speed fan. The controller manages the speed of each fan from a factory-set
minimum up to a factory-set maximum speed. The minimum fan speed is used whenever the A/C unit has no cooling operations
running. The maximum fan speed setting is used during times when the A/C unit is cooling. A dehumidification fan speed setting
is used when the system is in the dehumidification mode. The speed settings are adjustable in the Service>Blower>Blower Set Up
menu loop (see Section 4.5.5.5).
EC fan speed is automatically varied based on temperature. There are mechanisms to trade off the control valve opening versus
fan speed. When the system enters the dehumidification mode, the fan speed automatically changes to the dehumidification
speed setting.
The E2 controller's software is equipped with an operational fail-safe mode. Upon sensing a temperature sensor failure, the
controller signals an alarm. It continues to develop the CW valve and fan control outputs by calculating the averaged value of the
remaining sensors to replace the input value of the failed sensor. If all the temperature sensors fail, the controller develops the
control outputs based on the entered temperature setpoint value minus a 3° F temperature offset. Humidity control continues
based upon the setpoint. This allows the Cold Row system to continue operating while the cause of the problem is corrected.
The controller continually monitors fan operation. Cold Row CW units are equipped with a pneumatic air proving system
connected to a flow switch that detects the loss of airflow when a fan fails to operate. CRCW-24 units have larger fans that
include an intergrated electronic monitoring function. If any of the following failure conditions occur, the motor automatically
stops and an alarm is sent to the controller.
a. Locked rotor
b. Loss of a phase
c. Low main supply voltage
d. Overheating of electronics
e. Overheating of monitor
If one of the fans fails to operate, the controller alerts the operator with an alarm message and increases the speed of the
remaining two fans to 99.9% to compensate for the loss of airflow. If the fault does not clear, the fans shut down for 5 seconds
and then restart. If the fault continues, the fans reset a second time. If the fault does not clear after the second reset, the fan(s)
that generated the fault are shut down and the remaining fans continue operation at 99.9% speed.
If the BMS monitoring/control signal fails, the E2 controller will default to local operation at the current setpoints for the fan and
chilled water control valve. The local sensors have priority over the BMS system.
4.4.4.1 Independent Fan Speed Control
The system controller may be configured for independent, variable fan speed control for managing upper, middle, and lower zone
cooling. The controller continually monitors the actual cold aisle supply air conditions for each fan zone (upper, middle, and lower)
as determined by temperature sensors mounted locally to each zone inside the Cold Row cabinet, and it adjusts the speed of each
fan to meet the supply air temperature setpoint for that zone. The operator may select from three independent fan speed
temperature control methods in the Control> Set>Fan Control menu loop (Section 4.5.4.1). Minimum and maximum fan speed
settings for each fan are user adjustable in the Service>Blower>Temp Zone Set Up menu loop (see Section 4.5.5.4). The fans will
not run at speeds outside of the envelope established in that menu loop.
4.4.4.1.1 Variance from Average Fan Speed Control
When configured for variance from average fan speed control, each fan operates independently. The controller manages the
speed of each fan by comparing the variance of the fan's local zone temperature sensor to the overall average temperature
measured by the sensors for all three fan zones. The controller adjusts the speed of each fan as necessary to meet the supply air
temperature setpoint for that zone.
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Table of Contents
Troubleshooting
