Mechanical Cooling - Daikin MPS015 F Installation And Maintenance Manual

Mechanical Cooling

Constant Volume (Space Comfort
Controller)
The control temperature for a CAV unit is typically the space
temperature. A space temperature sensor must be field
installed into the occupied space and connected to the unit
controller.
The unit goes into the cooling mode of operation when the
control temperature (space temperature) is above the cooling
setpoint by more than ½ the deadband.
Example – the cooling setpoint is set to 70.0°F and the
deadband is 1.0°F, the unit will not go into the cooling mode of
operation until the space sensor reaches 70.6°F.
When this takes place, the cooling mode of operation will begin
and the 1st stage of compressor operation will start.
The unit controller will turn on the next stage of compressor
operation, or turn off a stage of compressor operation, to
maintain the cooling setpoint temperature within the deadband.
When a compressor stage turns on, the next compressor
stage, up or down, will not take place for the next 4 minutes.
This "4 minutes" is called the stage time. Reference the
"Cooling Setup" menu for the adjustable stage time value.
When a cooling stage is initiated no further operation will take
place within the stage timer limit. In the above example, the
unit will stage down or turn off the cooling mode of operation
when the cooling setpoint reaches 69.4°F.
Variable Air Volume (Discharge Air
Controller)
The unit's cooling mode of operation is controlled by the
control temperature, the change-over temperature, and the
discharge air temperature. The unit goes into the cooling mode
of operation by analyzing the control temperature. The control
temperature for a VAV system is the return temperature.
The unit goes into the cooling mode of operation when
the control temperature (return temperature) is above the
changeover setpoint by more than ½ the deadband.
Example – If the change over temperature is 70.0°F and the
deadband is 1.0°F, the unit will not go into the cooling mode of
operation until the return temperature reaches 70.6°F.
When this takes place, the cooling mode of operation will begin
and the 1st stage of compressor operation will start.
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The unit controller will turn on the next stage of compressor
operation, or turn off a stage of compressor operation, to
maintain the discharge air temperature setpoint within the
deadband. When a compressor stage turns on, the next
compressor stage up or down will not take place for the next 4
minutes. This "4 minutes" is called the stage timer.
When a cooling stage is initiated no further operation will
take place within the stage timer limit. Reference the Cooling
Setup menu for the adjustable stage time value. In the above
example, the unit will stage down or turn off the cooling mode
of operation when the return temperature reaches 69.4°F.
Economizer
When the economizer is enabled, the outside air temperature
is below the changeover setpoint, and the differential enthalpy
switch (if installed) is made, the economizer becomes the
first stage of cooling. It will modulate to control to either the
discharge air temperature (VAV) or space temperature (CV).
Every 4 minutes, the unit can then either add mechanical
cooling if the economizer is at 100% open, continue
economizing, or if the control temperature is satisfied, return to
minimum position and transition back to "Fan Only" mode.
If the enthalpy switch breaks or the outside air warms, the unit
will exit economizing and continue to mechanically cool while
returning to the minimum position for ventilation.
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