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OA mode. The mode can be activated programmatically as described above or
through the Building Management System (BMS) network.
• Purge Mode
Purge mode is used to clear airborne byproducts of the pool disinfection process
as required by the operator. This is typically done when the space is not occupied.
When the need is determined, a signal is given via a contact closure or through
the Building Management System (BMS) network. The unit will bring in the
specified amount of outdoor air (typically at a very high flow rate). During purge
mode the refrigeration system is disabled. The heating system is controlled from
the supply air temperature sensor only and the system is set to a point that only
avoids major condensation from occurring at the ducts and diffusers. In this way,
the energy required to clear the air of these byproducts is minimized while
avoiding issues with introducing very cold air.
In all modes the unit monitors the static pressure of the zone and modulates the exhaust
airflow rate to maintain the set point. Typically this is set to -0.050” WC. This means that the
exhaust air flow rate will be greater than the outdoor air flow rate to maintain this negative
static pressure. Building envelopes that are leaky may require much more exhaust air than
outdoor air. The amount of outdoor air in each mode may be limited through the controls if
desired, but the space must be kept at a negative static pressure in order to avoid mold and
property damage.
Note that condensation may occur when cold outdoor air is mixed with warm, humid return
air inside the dehumidifier. During the winter months, this moisture can freeze and cause
serious damage to the equipment. Desert Aire dehumidifiers are equipped with an internal
temperature sensor which will close the outdoor air damper if senses freezing temperatures
inside the unit.
If outdoor temperatures in your area drop below 32°F, and outdoor air code compliance is
required at all times, you may need to install an optional preheating coil. System failures
caused by improper outdoor air duct installations are not covered by the Desert Aire warranty.
The intake mounted sensor (if sensor installed in the unit) or the zone sensor determines the
current temperature and RH of the space.
5.5.2 Blower Operation
The following is the blower control sequence for the standard SP control system:
• The SP unit will run to achieve a constant supply airflow as initially programmed in
the unit controller per order specifications. Measurement through the included
supply and exhaust blower’s venturi is used for this automatic operation.
• The exhaust fans will run to achieve a negative static pressure in the zone. This
airflow rate can be read on the CM3560 controller display.
Desert Aire - SP Manual
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