Daikin MicroTech III Operation Manuals page 104

Reset Temperature Limit
The user has the option of setting a low temperature limit that
will override all the outdoor air reset functions described in this
section except the Return Fan Capacity Override function if the
discharge air temperature or entering fan temperature gets too
cold as a result of the reset . The user can choose the override
sensor by setting the Reset Temperature Limit to None, DAT or
EFT . When set to None the Reset Temperature Limit function
is disabled . A Reset Temperature Limit PI_Loop will be used
to reset the minimum outside air damper setpoint downward
when the selected temperature input drops below the Reset
Temperature Limit .
Minimum Position Control -Field Supplied Outdoor
Airflow Station Input
When the OA Flow Station parameter in the Software
Configuration Code is set to Field Station and the Field Station
parameter on the keypad is set to VDC or mA, the Minimum
OA Position value is adjusted based on the measured amount
of outdoor air being brought into the unit from a field supplied
airflow monitoring station. If the airflow is below the desired
value, the Minimum OA Position is increased and if the airflow
is above the desired value, Minimum OA Position is decreased .
The field airflow signal will be in the form of a 0-10V or 0-20 mA
input . The minimum and maximum sensor input values (0-10V
or 0-20 mA) and the corresponding minimum and maximum
CFM values are user editable .
NOTE: The Minimum OA Position is reset up and down
between the Ventilation Limit and the Demand
Control Ventilation Limit by a PI_Loop function to
maintain the field OA CFM value at an adjustable OA
CFM Setpoint .
When the MinOAType is set to Ext or IAQ and the
Field OA Station parameter is set to VDC or mA, the
OA flow input is assigned to a specially added I/O
expansion module (EXPE) position X1 . When the
MinOAType is not set to Ext or IAQ and the Field OA
Station parameter is set to VDC or mA, the OA flow
input is assigned to the main control board(MCB)
position X1 .
Minimum Position Control - Design Flow (RPS
Airside Economizer Units Only)
When the OA Flow Station parameter in the Unit configuration
menu is set to Design Flow and the Design Flow control
flag is set to Yes, the minimum outside air damper position
is controlled to maintain the minimum OA flow setpoint.
Design Flow is only available when for RTU units with Airside
Economizers .
When the DesignFlow control flag is set to Yes, the Minimum
OA Position value is adjusted based on the measured amount
of outdoor air being brought into the unit using a PI_Loop
function. If the airflow is below the desired value, the Minimum
OA Position is increased and if the airflow is above the desired
value, Minimum OA Position is decreased .
OM 920-6 • MICROTECH UNIT CONTROLLER
NOTE: The factory default for Min OA Reset is set to none
however changes may be made by accessing the Min
OA Set-Up menu . Once changes have been made to
the Min OA Reset type, the Apply Changes flag must
be changed from no to yes in order for the controller
to recognize the changes . Setting the Apply Changes
flag to YES will automatically reset the controller.
0-30%OA Units
A two position 0-30% OA actuator is controlled by a modulating
analog output . This actuator is driven to its fully open position,
nominally 30%, 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 desired minimum
open position between 0% and 30% normally is set by an
editable keypad menu item (Vent Limit) . If a valid value is
provided via the network, that position is used as the desired
minimum open position instead of the keypad value .
The two position damper is driven to the closed position when
the supply fan is OFF (OFF and Startup state), the unit is in the
Recirculation state, unoccupied operation is active, or the fan
has been on for less than the Zero OA Time . As a result the
OA dampers are driven closed in night setback, night setup,
morning warm-up, and morning cool down situations . The two
position damper is driven to the desired minimum open position
in all other conditions .
The Ventilation Limit equals the keypad editable Vent Limit
and the Demand Control Ventilation Limit equals the keypad
editable DCV Limit . The Vent Limit cannot be set higher than
the 0-30%OAMax value . The DCV Limit cannot be set higher
than the Vent Limit .
Return Fan Capacity Override (RTU Airside
Economizer Units Only)
The minimum position determined by any method below
may be overridden for a variable speed return fan when the
return fan speed is below the supply fan speed by more than
an adjustable value. In this situation, the outdoor air damper
minimum position is reset up based on the schedule shown
below if normal control of the minimum position would result in
a lower value . The minimum position will be controlled in the
normal manner if that results in a higher value than determined
by the reset schedule .
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