100% Outside Air Damper Control; Two Position; Airside Economizer; Economizer To Cooling Operating State - Daikin MicroTech III Operation Manuals

Table 50: Outdoor Air Damper Minimum Position Reset
Schedule
Discharge Fan
<= 20% Min Fan
Speed – Return
Differential
Fan Speed
Outdoor Air
Demand Control
Damper Minimum
Ventilation Limit
Position
NOTE: If the supply fan is a constant volume fan, the
Supply Fan Speed is assumed to be 100% when
the discharge fan is on . If the Min Fan Differential
is set equal to the Max Fan Differential, the return
fan capacity override value reverts to the Ventilation
Limit . This capability is not provided for exhaust fans .
Building Static Pressure Override (Airside
Economizer Units Only)
The minimum position determined by any method described
below may be overridden for a variable speed return fan or
exhaust fan controlled by building static pressure when the
return fan speed is at minimum or the exhaust fan has been
stopped due to low building static pressure if the building
pressure remains negative . If the user elects to use this function
and the return fan has been at the minimum speed or the
exhaust fan has been stopped for a minimum return/exhaust fan
off time (default = 120 seconds) a PI_Loop will begin modulating
the Min OA Pos setpoint upward to maintain the building static
pressure at the building static pressure setpoint .
100% Outside Air Damper Control, Two
Position
100% OA two position actuators are controlled by a digital
output for SCU unit and by a modulating analog output for
RTU units .
• Digital Output - The OA damper is driven fully open when
the digital output is On and fully closed when the digital
output is OFF
• Analog Output (100% OA Units) - The OA damper is
driven to its 100% open position when the OA damper
analog output is at its maximum value and it is driven
closed when the OA damper analog output is at its
minimum value
The OA damper is open during the Start Initial period, and
it remains open during all operating states . The OA damper
remains open after the fan is turned off until 30 seconds after
the Airflow Switch digital input indicates loss of airflow. This
keeps the outside air dampers open in case there is a failure
or external override that keeps the fan running after it is turned
OFF by controller logic . If the fan is turned ON by bypassing the
controls that have it OFF, the Damper Output is NOT turned ON .
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Between Min and >= 50% Max Fan
Max Differential Differential
Linear
Ventilation Limit
Interpolation

Airside Economizer

If a unit is equipped with a 0-100% modulating economizer,
and the outdoor air is suitable for free cooling, the unit attempts
to satisfy the cooling load by using outdoor air before using
mechanical cooling . When the control temperature is above
the Occupied or Unoccupied Cooling Set Point by more than
half the Occupied or Unoccupied Cooling Dead Band and the
discharge air temperature is above the Discharge Cooling Set
Point by more than half the Discharge Cooling Dead Band, the
controller enters the Econo state . When the unit is in the Econo
operating state, the outdoor air dampers are modulated as
required to maintain the Discharge Cooling Set Point .

Economizer to Cooling Operating State

The transition from the Econo to Cooling operating state
occurs when the economizer is unable to satisfy the cooling
load and mechanical cooling is available . This will occur when
the commanded economizer position indicates more than 95%
open and the discharge air temperature (DAT control units) or
control temperature (Zone control units) is above the applicable
Cooling Setpoint by more than half the applicable Cooling
Deadband for longer than the Cooling Interstage Timer .

Waterside Economizer

If a unit is equipped with a 0-100% modulating waterside
economizer, and the conditions are suitable for free cooling,
the unit attempts to satisfy the cooling load by using waterside
economizer before using mechanical cooling . When the control
temperature is above the Cooling Enable Set Point by more
than half the Cooling Enable Dead Band and the discharge
air temperature is above the Discharge Cooling Set Point
by more than half the Discharge Cooling Dead Band, the
controller enters the Econo state . When the unit is in the Econo
operating state, the economizer valve is modulated as required
to maintain the Discharge Cooling Set Point .
Economizer FDD
The economizer fault detection and diagnostics function
provides warning alarm indication of over economizing, under
economizing, stuck dampers and excess outdoor air . This
function is available when a fault detection type of OA damper
is selected in the unit configuration menu. Once it is selected
via the unit configuration menu it can be disabled/enabled via
the Economizer set-up menu .
105 OM 920-6 • MICROTECH UNIT CONTROLLER
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