Contact: AIRSYS North America Phone: (855) 874-5380 Page 67 of 112
Email: ASNSupport@air-sys.com Web: http://airsysnorthamerica.com Rev 1.15
Operational Logic:
Free Cooling (Economizer) Operation
When Free Cooling (FC) is engaged, the damper opens to introduce cooler air from outside to be
delivered to the shelter. The damper will open when the difference between the indoor and outdoor
temperatures is larger than a predefined minimum (default 3.6°F, configurable under “Free Cooling” in the
Control Configuration menu) and the outdoor humidity is below the limit (default 85%).
The supply fan will start at low speed when the damper opening conditions are met and the indoor
temperature is above the Free Cooling Setpoint (configurable under “Room Temperature” in the User
Configuration menu). As the indoor temperature rises, the fan speed will increase to keep the indoor
temperature within 2°F of the main setpoint. If the indoor temperature cannot be maintained below the
lead compressor turn on point (configurable under “Setpoints” in the Control Configuration menu), the
compressor will start to assist FC.
During cold weather, the outdoor damper modulates to keep the supply air temperature above 51.8°F
and will close completely when the supply temperature is below that point (configurable under
“Setpoints” in the Control Configuration menu). The damper will also close if the humidity is above the
limit (default 85%) or if the AFPD dust sensor triggers a protection event.
If partial free cooling is allowed (default enabled), the damper can remain open when the compressor is
engaged, provided that the outdoor temperature is lower than the indoor temperature. Otherwise, the
damper will close as soon as the compressor starts. For shelters without a secondary pressure relief (e.g. a
barometric louvre), partial free cooling can be disabled (configurable under “Free Cooling” in the Control
Configuration menu).
Mechanical Cooling Operation
All AIRSYS Precision Cooling WPUs have variable speed compressors which will adjust their speed to
match the heat load inside the shelter. The compressor logic will vary based on whether free cooling is
engaged. If free cooling is enabled, the compressor will not start until the indoor temperature has reached
a predetermined level above the setpoint (default 2°F). At that point, the compressor will start at full
speed and adjust its speed according to the indoor temperature. These settings can be configured under
“Setpoints” in the Control Configuration menu.
Heater Operation
The heater will activate when the indoor temperature reaches a predetermined level below the setpoint
(default 29°F). The heater will then run until the temperature is a certain level above the on point (default
3°F). These settings can be configured under “Setpoints” in the Control Configuration menu.
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