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XTE 802 Series Walk-In-Cabinet (WIC) Description & Installation Manual (631-205-434)
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Rev. D
111
DIRECT AIR COOLING (DAC) AND HVAC
Description
The climate control configuration for the F2018009 WIC consists of a Direct Air Cooling (DAC) unit and a
HVAC unit, both controlled by a common controller.
Refer to the DAC, HVAC, and controller manufacturer documentation for operating instructions. The most
current versions of these manuals can be found at https://www.airxcel.com/marvair.
for a typical schematic of the DAC and HVAC systems installed in this WIC.
Alarm circuits from the controller are factory connected to the WIC alarm blocks. See
on page 108.
General Operation
The controller monitors internal WIC temperature and controls the operation of the DAC unit to provide cooling
for the equipment installed in the WIC. The controller also operates a second HVAC unit that provides
additional cooling when the DAC is unable to maintain the desired cooling temperature set point. The HVAC
unit also serves as a backup in the event of failure of the DAC unit.
On a call for cooling from a temperature sensor located in the WIC, the fan in the DAC unit turns on and both
the outside air damper in the unit and the external exhaust damper open. The fan speed varies based on the
difference between the current WIC temperature and the first stage cooling set point temperature. As the
temperature approaches the set point, the fan speed increases to a maximum of 100% of rated air flow and, as
the temperature recedes from the set point, the fan speed decreases to the minimum of 5% of rated air flow. If
the DAC is operating and the temperature rises above the first stage cooling set point, the DAC will continue to
operate and the evaporator blower in the air conditioner will turn on. If the temperature rises above the second
set point temperature, the DAC is turned off, the motorized damper and exhaust damper are both closed and
the air conditioner turns on in mechanical cooling. The air conditioner runs until the temperature drops below
the mechanical cooling disable set point. At this point, the DAC is turned on and both the motorized damper
and exhaust damper are opened. The air conditioner can also be turned on to provide a comfortable working
temperature when technicians are in the WIC. Any time the air conditioner is providing mechanical cooling, the
DAC is turned off and all louvers are closed.
