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Microprocessor Controller for DOAS

Sequence of Operation

The microprocessor controller can be configured for
air handler, energy recovery, and dedicated outdoor air
systems. Each application utilizes similar technologies
for heating and cooling: chilled water, hot water, indirect
gas, electric heat, and packaged or split DX cooling. All
set points, lockouts and delays are user adjustable via
the integral keypad display, remote display, or web user
interface.

General Operation

UNIT START COMMAND:

The microprocessor

controller requires a digital input to enable operation.
The unit can then be commanded on or off by this
digital input, keypad, the BMS or schedule. When a
start command becomes active the following steps
occur:
• Energy recovery wheel starts, if equipped
• Factory mounted and wired dampers are powered

(Outside air, exhaust air, and recirculation air
dampers, if equipped)

• Exhaust fan, if equipped, starts after adjustable delay
• Supply fan starts after adjustable delay
• Tempering operation starts after adjustable delay

UNIT STOP COMMAND:

A shutdown occurs when

there is not an occupied or unoccupied start command.
The following shutdown methods can occur.
Hard shutdown occurs under the following conditions:

• A user or the BMS disables the system, and the

supply temperature is less than the soft shutdown
enable set point.

• Occupancy is commanded to unoccupied while there

is no unoccupied start command, and the supply
temperature is less than the soft shutdown enable
set point.

When a hard shutdown occurs:
• The unit shuts down immediately.
• Dampers spring-return to their off position. Damper

power is cut 30 sec. after the fans. This allows
the fans to slow down prior to spring closing the
dampers.

Soft shutdown occurs under the following conditions:
• A user or the BMS disables the system, and the

supply temperature is greater than or equal to the
soft shutdown enable set point.

• There is no unoccupied or occupied start command

and the supply temperature is greater than or equal
to the soft shutdown enable set point.

The following occurs during a soft shutdown:
• Tempering outputs immediately revert back to their

off value; while

• Dampers remain open and fans continue to run; until
– The supply air temperature falls below the soft

shutdown enable set point minus 5.0°F; or

– The soft shutdown delay timer has expired.

UNIT/SYSTEM DISABLED COMMAND:

The unit becomes disabled due to the following:
• The unit was disabled from the controller’s Unit

Enable screen.

• The unit enable digital input changes to the disabled

state.

• The unit was disabled from the BMS.
• The remote start input is in the off position.
• The shutdown input is in the shutdown position.
• A system shutdown alarm was activated.
When disabled the following actions occur:
• The unit shuts down immediately; and
• Dampers spring-return to their off position.

OCCUPANCY:

The microprocessor controller offers

five modes of determining occupancy: digital input,
occupancy schedule, BMS, always occupied, or always
unoccupied. When in the unoccupied mode, the unit
can be configured to shut down, or cycle on to maintain
the unoccupied space set points. The unit can be
temporarily overridden to the occupied mode via a
digital input, keypad display, or space thermostat, if
equipped.
•

Occupied Mode:

   -  Exhaust fan on, if equipped
   -  Supply fan on
   -  Energy Recovery Wheel Control (refer to

Energy Recovery Wheel section), if equipped

- Damper Control (refer to Outside Air and

Recirculated Air section), if equipped

   -  Heating (refer to Heating section)
   -  Cooling (refer to Cooling section)
  •

Unoccupied Mode:

Unit Off:

Unit remains off when in unoccupied

mode.

Normal operation with unoccupied set points:

Unoccupied mode will operate as if in occupied
mode but will utilize adjustable unoccupied set
points.