Daikin DPS - Cooling

Cooling
(See page 41 for more information)
Entering the Cooling Operating State
The unit enters the Cooling operating state from the Fan Only
operating state when the control temperature rises above the
Occupied Cooling Set Point by more than half the Occupied
Cooling Dead Band and the discharge air temperature is above
the discharge cooling setpoint by more than half the Occupied
Cooling Dead Band. The unit transitions from Cooling to Fan
only when the control temperature falls below the Occupied
Cooling Set Point by more than half the Occupied Cooling
Dead Band. The unit will also transition from the Cooling to Fan
only operating state if Cooling operation is disabled due to OA
ambient lockout.
DAT Control
In the Cooling state, compressors are modulated to maintain
the Discharge Air Temperature at the Discharge Cooling
Setpoint.
Zone Control
In the Cooling state, compressors are turned ON and
modulated to maintain the control temperature at the Occupied
Cooling Setpoint.
When Dehumidication is active, compressors are modulated
to maintain the leaving coil temperature at the minimum leaving
coil setpoint.
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
Discharge Air Temperature Setpoint
Reset - Cooling
The Cooling DAT Setpoint may be reset for units with DAT
Cooling Control. The reset type may be set to one of the
following:
• None: Discharge Cooling Spt is user adjustable
• Network: Discharge Cooling Spt is equal to the Network
DAT Clg Setpoint when it is valid
• Space: Discharge Cooling Spt is based on the Space
Sensor
• Return: Discharge Cooling Spt is based on the Return Air
Sensor
• OAT: Discharge Cooling Spt is based on the Outdoor Air
Temperature
• Ext mA: Discharge Cooling Spt is determined by a 0-20
mA signal
• Ext V: Discharge Cooling Spt is determined by a 0-10
VDC signal
• Airow: Discharge Cooling Spt is based on the airow as
indicated by the variable frequency drive speed
Reset reverts from Return to None when a Return Air Sensor
opens or shorts. Reset reverts from Space to None when a
Space Sensor opens or shorts. Reset reverts from OAT to
None when an Outdoor Air Sensor opens or shorts.
When Space, Return, OAT, Airow, Ext mA, or Ext V is
selected, the Discharge Cooling Spt equals the Max Clg Spt
when the selected value equals the Max Clg Spt @ value.
Similarly, the Discharge Cooling Spt equals the Min Clg Spt
when the selected value equals the Min Clg Spt @ value.
When Space, Return, OAT, or Airow is selected, the reset
schedule should be set so that the DAT Cooling setpoint
decreases as the selected temperature increases as shown in
the graph below.
Figure 19: Cooling Setpoint
operator’s guIde
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