Reset - Cooling - Daikin MicroTech III Operation Manuals

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
• Airflow: Discharge Cooling Spt is based on the airflow 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, Airflow, 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 Airflow 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 .
Figure 17: Cooling Setpoint
OM 920-6 • MICROTECH UNIT CONTROLLER
When Airflow is selected, the values "Min Clg Spt @" and
"Max Clg Spt @" are entered as percentage values . When
Ext mA is selected, the values "Min Clg Spt @" and "Max Clg
Spt @" are entered as mA values . When Ext VDC is selected,
the values "Min Clg Spt @" and "Max Clg Spt @" are entered
as VDC values .
If Ext mA or Ext V is selected as the type of reset, the Min Clg
Spt @ value may be set above the Max Clg Spt @ value to
cause a decrease in the DAT setpoint as the external signal or
the Min Clg Spt @ value may be set below the Max Clg Spt @
value to cause an increase in the DAT setpoint as the external
signal increase .
The Min Clg Spt @ value can be set below the Max Clg Spt
@ value for all types of reset, but it only makes sense for
external reset .
When ever the Clg Reset Type or Engineering Units is
changed, the Min Clg Spt @ and Max Clg Spt @ values revert
to default values as follows:
• None: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Network: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Space, Return: Min Clg Spt @=73 .0F, Max Clg Spt
@=71 .0F
• OAT: Min Clg Spt @=90 .0F, Max Clg Spt @=70 .0F
• ExtmA: Min Clg Spt @=4 .0mA, Max Clg Spt @=20 .0mA
• ExtVDC: Min Clg Spt @=0 .0V, Max Clg Spt @=10 .0V
• Airflow: Min Clg Spt @=33%, Max Clg Spt @=100%
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