Recirculating Operating State; Fan Only; Min Dat; Heating - Daikin MicroTech III Operation Manuals

Recirculating Operating State

Units with return air always enter the Recirculating operating
state after the completion of the Startup operating state .
In the Recirculating operating state fans are started and
operate while the outdoor air dampers remain closed . This
allows temperature conditions throughout the unit and space
to equalize before temperature control begins . Cooling and
heating remain disabled . The unit remains in the Recirculating
operating state until the Recirculate State Timer (default 180
seconds) expires .
NOTE: 100% outdoor air units do not transition through the
Recirculating operating state .

Fan Only

The unit enters the Fan Only operating state after the
recirculation timer expires. Units configured for 100% outside
air operation will transition directly from the Start up operating
state into the Fan Only operating state . Once entering the Fan
Only state of operation the unit will then, based on sensor
inputs transition into any of the 4 remaining states of operation
- heating, cooling, economizer, or minimum discharge air

heating .

Min DAT

If heating is enabled and there is no heating load (normally
FanOnly operating state), the controller activates the units
heating equipment as required to prevent the discharge air
temperature from becoming too cool if the Min DAT Control
Flag is set to yes via the Heating menu (Commission Unit/
Heating/MinDAT Ctrl) . The unit enters the Min DAT operating
state during occupied operation when neither cooling nor
heating is required based on the heat/cool changeover
function but the discharge temperature falls below a minimum
discharge temperature limit . If the discharge air temperature
falls below the this minimum discharge temperature limit
by more than half the discharge heating deadband, the unit
operating state changes from Fan Only to Min DAT . The
unit transitions out of the Min DAT operating state once the
discharge air temperature is above minimum discharge
temperature limit and the heating capacity has been at its
minimum position for the duration of the heating stage timer .
NOTE: On VAV or CAV discharge control units, the DAT
cooling setpoint parameter in the Cooling menu acts
as the minimum discharge temperature limit . On CAV
zone control units the Min DAT Limit parameter in
the Heating menu acts as the minimum discharge
temperature limit .
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Heating
The unit enters the Heating operating state when the control
temperature falls below the Occupied or Unoccupied Heating
Setpoint by more than ½ the occupied or unoccupied heating
deadband . During the Heating operating state, the outdoor air
dampers are either 100% open if the unit is a 100% outdoor air
unit or controlled to the minimum outside air position . Cooling
is disabled .

Economizer

If the unit is equipped with a 0-100% modulating economizer
(waterside or airside) and the conditions are suitable for free
cooling, the unit attempts to satisfy the cooling load by using
either outdoor air or the waterside economizer before using
mechanical cooling .
If the unit is configured for Zone Temperature Control the
transition to economizer operation will occur if all the following
are true:
• The control temperature rises above the occupied or
unoccupied cooling setpoint by more that ½ the occupied
or unoccupied cooling high deadband
• The discharge air temperature is greater than the Min
DAT limit by more than ½ the DAT
• heating deadband . This will prevent more cold air from
being brought in when the DAT is already cold
• The economizer operation is not disabled
If the unit is configured for Discharge Air Temperature Control
the transition to Mechanical cooling will occur if all the following
are true:
• The control temperature rises above the occupied or
unoccupied cooling setpoint by more that ½ the occupied
or unoccupied cooling deadband
• The discharge air temperature is greater than the DAT
cooling setpoint
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