Desert Aire Aura QS, Installation And Operation Manual

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The unit constantly measures the IA humidity and temperature. The controller
calculates the IA dewpoint. When the IAQ conditions are above the dewpoint set point
of the system, the dehumidification mode will be enabled. This condition will take
priority over any heating or cooling modes. With an IA dewpoint set point of 55°F, the
supply air dewpoint will be held at or below 55°F, and the SAT will be held at the SAT
set point. Although the dewpoint will never go above 55°F, during low load days the
supply air dewpoints could be lower. Once the moisture is removed to below the
design dewpoint condition, the controller modulates the hot gas reheat coil to warm the
supply air to the desired SAT set point. The SAT set point is a programmable value on
the IAQ standard controller. Any excess reheat energy not used for reheat is either
rejected to the remote condenser or to the water loop.
Since the unit is constantly measuring the IA temperature, an IA condition below the
heating set point will place the unit in the heating mode. Any temperature above the
cooling set point will place the unit in a cooling mode. Again, these modes will only
occur when the unit is NOT in its dehumidification mode. When the IA temperature
is between the heating and cooling set point and dehumidification is not required,
un-conditioned air will be provided to the space. This condition is commonly referred
to as an Economizer Mode.
5.4.2 Blower Operation
The following is the blower control sequence for the standard IAQ control system.
In all cases, the blower will not run in an alarm condition. If the blower cycles off, the
blower will remain off for a minimum of 1 minute to avoid the possibility of rapid cycling,
specifically from the automatic reset safety devices.
When the blower operation is set for CONTINUOUS, the blower will run in all cases
except when a compressor is commanded ON and a low suction pressure condition
exists.
When the blower is set for FIELD DAMPER, the blower will run if the unit is in the
OCCUPIED mode and the DAMPER END SWITCH is activated, indicating the damper
is fully open. However, the exception that overrides the FIELD DAMPER setting is if a
compressor is commanded ON and a low suction pressure condition exists.
When the blower is set for MIXING BOX, the blower will run if the unit is in the
OCCUPIED mode, except when a compressor is commanded ON and a low suction
pressure condition exists. If the unit is in the UN-OCCUPIED mode, the blower will
run on a call for unoccupied dehumidification, cooling or heating (not economizer
mode), except if a compressor is commanded ON and a low suction pressure
condition exists.
Desert Aire - QS/QV Manual