Mechanical Cooling; Determining Unit Status; Determining Control Mode - Daikin MicroTech III Operation Manuals

Mechanical Cooling

The unit enters the mechanical cooling operating state when
cooling is required and the economizer is disabled, not present,
or already fully open .
If the unit is configured for Zone 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 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 disabled or not present
• Mechanical cooling is enabled
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 by more than ½ the DAT cooling
deadband
• Post heat operation is complete
• Economizer operation is disabled
• Mechanical cooling is enabled

Determining Unit Status

Unit Status is a status only item which indicates whether or not
the unit is enabled and if not why .
Enabled
Unit operation has not been disabled for any of the following
reasons .
Off Manual
The unit operating state is OFF and the unit status is OffMan
when the control mode is set to OFF via the keypad . The
control mode can only be changed via the System menu on the
keypad/display .
OffManCtrl
The unit operating state is OFF and the unit status is OffManCtl
when the controller is set to manual control via the Manual
Control menu .
Off Network
The unit operating state is OFF and the unit status is OffNet
when the control mode is set to Auto via the System menu and
the network Net App Mode is set to OFF .
OM 920-6 • MICROTECH UNIT CONTROLLER
Off Alarm
The unit operating state is OFF and the unit status is OffAlm
when an active alarm of the "fault" type has the unit shutdown .
Off Fan Retry
The unit operating state is OFF and the unit status is OffFnRty
when The fan retry conditions below indicate that the unit
should be shutdown and restarted after airflow is lost.
• The supply fan is controlled by a VFD
• The airflow switch (PC7) is open AND the duct static
pressure is less than ½ the duct static pressure setpoint
• There are no active faults that would shut down the unit

Determining Control Mode

The unit cooling and heating can be set up for automatic
heat/cool, cool only, heat only, fan only, or network cool/heat
operation by setting the Control Mode . The unit can also be
manually disabled via the Control Mode . The following are
descriptions of the six available Control Mode selections .
OFF
When the Control Mode is set to "OFF," the Unit Status is
"Off Man" and the unit is completely disabled .
Heat Only
When the Control Mode is set to "Heat Only," heating operation
is allowed to operate to maintain the heating set points .
Cooling operation is disabled (Cooing Status is "Off Man") .
Cool Only
When the Control Mode is set to "Cool Only," cooling operation
is allowed to operate to maintain the cooling set points . Heating
operation is disabled (Heating Status is "Off Man") .
Fan Only
When the Control Mode is set to "Fan Only," the fans are
allowed to operate but cooling and heating operation is
disabled (Cooling Status and Heating Status are "Off Man") .
Heat Cool
When the Control Mode is set to "Heat/Cool," both cooling
and heating operation are allowed to operate as required to
maintain the cooling and heating set points .
Auto
When the Control Mode is set to "Auto," the heat/cool, cool
only, heat only, and fan only decision is determined by
the network application mode parameter, which is set via
a network signal as described below . The NetApp Mode
parameter has no effect on unit operation unless the Control
Mode is set to "Auto ."
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