100 ● gForce Ultra User Manual 10-2014
9. Control Logic
The following describes the implementation of the gForce Ultra logic with dap4™
controller.
9.1 Fan Control Logic
There are six (6) different fan speed mode in DX logic:
Fan Speed Modulation to Rack Temperature (Mod to Rack)
Fan Speed Modulation Proportional to Cooling Demand (Mod to Comp)
Fan Speed Modulation to Return Air (RA) Temperature (Mod to RetT)
Fan Speed Modulation to Constant Static Pressure (Air Pressure)
Fan Speed Modulation based on BMS (BMS Speed)
Constant Fan Speed (Const Speed)
9.1.1 Fan Speed Modulation to Rack Temperature (Mod to Rack):
In this mode the DX fan speed modulates based on rack temperature. Modulation to
Rack Temperature “Mod to Rack” mode is found under Menu J – Factory Settings, Fan
Settings.
The fans are controlled based on the maximum rack temperature. A single sensor is
standard. Two additional sensors are available as an option. If additional sensors are
installed, the control logic will be based on the highest value.
The fan will operate on rack air SP (Setpoint) and DB (Deadband) as follows:
• When the Maximum Rack Temperature is increasing:
If the Maximum Rack Temperature is greater than the Rack Temperature SP plus
the (DB), the fans will start to ramp up from minimum allowable speed.
If the Maximum Rack Temperature is greater than or equal to Rack Temperature
SP plus DB plus 1°F, the fans will run at maximum speed.
• When the Maximum Rack Temperature is decreasing:
If the Maximum Rack Temperature is less than the Rack Temperature SP plus
1°F, the fans will start to ramp down from allowable speed.
If the Maximum Rack temperature is less than or equal to Rack Temperature SP,
the fans will run at minimum speed.
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