Cooling: Modulating - Daikin MicroTech III Operation Manuals

Staging - Zone Control
In the Cooling state, compressor stages are turned ON and
OFF to maintain the control temperature close to the Occupied
or Unoccupied Cooling Setpoint. Use of the Projected Control
Temperature reduces overshoot during cool down . See the
Project Ahead section for a description of how the Project
Ahead Temperature is calculated .
When the unit enters the Cooling state or dehumidification
operation begins the unit goes directly to Cooling Stage # 1
so that the first compressor is turned on immediately.
During normal cooling operation the number of compressor
stages increases when the time since the last stage
change exceeds the Cooling stage timer, Projected Control
Temperature is greater than the Occupied or Unoccupied
Cooling Setpoint by more than half the deadband, the Control
Temperature is greater than the Occupied or Unoccupied
Cooling Setpoint by more than half the deadband, and the
Discharge Air Temperature is greater than the minimum DAT
cooling setpoint .
During normal cooling operation the number of compressor
stages decreases when the time since the last stage change
exceeds the cooling stage timer, the Projected Control
Temperature is less than the Occupied or Unoccupied
Cooling Setpoint by more than half the deadband, the Control
Temperature is less than the Occupied or Unoccupied Cooling
setpoint by more than half the deadband .
During normal cooling operation the compressor stages also
decrease when the time since the last stage change exceeds
the cooling stage timer, and the discharge air temperature is
less than the minimum DAT Cooling setpoint .
When Dehumidification is active, compressor stages are
controlled to maintain the leaving coil temperature between the
minimum leaving coil setpoint and the maximum leaving coil
DAT setpoint .
During dehumidification on operation, the number of
compressor stages increases if the time since the last stage
change exceeds the cooling stage timer and the leaving
coil temperature is greater than the Maximum Leaving Coil
Setpoint. During dehumidification operation, the number of
compressor stages decreases if the time since the last stage
change ecxeeds the cooling stage timer and the leaving coil
temperature is less than the Minimum Leavaing Coil Setpoint .
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Project Ahead
This section describes the Projected Control Temperature
used to turn on and off stages of heating and cooling for Zone
Control units . It is not used in DAT Control units .
In Zone Control cooling and heating operation, the Projected
Control Temperature, reduces overshoot as the zone
temperature approaches a setpoint after startup . It does this
by causing stages to stop increasing before the actual control
temperature reaches the setpoint . The rate of change of the
control temperature is calculated once per minute by the
controller and equals the change during the last sixty seconds .
This rate of change is multiplied by the Effective Project Ahead
Time and is added to the current control temperature . The rate
of change may be negative or positive so the Projected Control
Temperature may be higher or lower than the actual control
temperature. This value, the Projected Control Temperature, is
the temperature that would exist after the Project Ahead Time
passes if the control temperature were to continue to change
at the same rate for the Effective Project Ahead Time. The
Effective Project Ahead Time is set equal to the Cooling Project
Ahead Time when the unit is in the Cooling state . The Effective
Project Ahead Time is set equal to the Heating Project Ahead
Time when the unit is in the Heating state . It is set equal to
zero under all other conditions causing the Projected Control
Temperature to equal the actual control temperature

Cooling: Modulating

Modulating Cooling Control: Chilled Water
When the unit's cooling type is set to chilled water and is in the
Cooling operating state, or in the dehumidification operating
state the chilled water valve is modulated to maintain the
discharge air temperature at the Discharge Cooling Set Point
(or leaving coil temperature at the Minimum Leaving Coil
Setpoint if dehumidification is active).
Modulating Cooling Control: Face & Bypass
When the unit's cooling type is set to Face & Bypass and
is in the Cooling operating state, or in the dehumidification
operating state, the chilled water valve is driven fully open
and the face and bypass dampers are modulated to maintain
the discharge air temperature at the Discharge Cooling Set
Point (or leaving coil temperature at the Minimum Leaving Coil
Setpoint if dehumidification is active).
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