Microprocessor Controller for DOAS
5
®
Economizer
If the application requires cooling, and the outdoor
air conditions are suitable for free cooling, the
controller may enter the economizer state. If the unit is
economizing and the discharge temperature setpoint is
not being met, the controller may bring on mechanical
cooling. If equipped with a modulating outdoor air and
recirculated air damper, the dampers will modulate
between the minimum OA and maximum positions to
maintain the supply temperature setpoint. If equipped
with an energy wheel, Reference Energy Recovery
Wheel Sequence.
•
Temperature:
The economizer will be locked out
when:
- The outside air is greater than the economizer
high lockout (65°F).
-
The unit is operating in dehumidification mode.
-
There is a call for heating.
•
Temperature/Enthalpy:
The economizer will be
locked out when:
- The outside air is greater than the economizer
high lockout (65°F dry-bulb).
- The outside air is greater than the economizer
high enthalpy lockout (23 btu/lb).
-
The unit is operating in dehumidification mode.
-
There is a call for heating.
Dehumidification
The cooling is controlled to maintain the cold coil
setpoint. The dehumidification sequence will be locked
out when the OA is less than the dehumidification
lockout (10°F) above the cold coil setpoint. If equipped
with BMS communications, the user can also directly
set the cold coil leaving air setpoint.
•
Optional Room Relative Humidity Sensor or
Thermostat:
The controller will adjust the cold
coil leaving air temperature setpoint between the
minimum (50°F) and maximum (55°F) setpoint to
satisfy the desired room relative humidity setpoint.
Reheat
While the unit is in dehumidification mode, the supply
air can be reheated via Primary Heating Source, On/Off
Hot Gas Reheat or Modulating Hot Gas Reheat.
•
Modulating Hot Gas Reheat (valve):
The
microprocessor controller will modulate the hot gas
reheat valve to maintain the supply temperature
setpoint.
•
Reheat Plus:
The primary heat source configured to
act as secondary reheat.
Supply Fan VFD Sequence
The factory installed VFD is wired to the controller.
Supply fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the supply fan speed.
•
Optional Space/Duct CO
2
Sensor:
The controller
will modulate the supply fan based upon a
comparison of the CO
2
setpoint to the actual CO
2
levels reported from the sensor.
•
Optional Duct Static Pressure Sensor:
The
controller will modulate the supply fan based upon
a comparison of the duct static pressure setpoint to
the actual duct static pressure level reported from the
sensor.
• Optional Building Static Pressure Sensor:
The
controller will modulate the supply fan based upon a
comparison of the building static pressure setpoint to
the actual building static pressure level reported from
the sensor.
•
Optional Single Zone VAV (SZ):
The controller will
control the supply air temperature and supply fan
speed to maintain the room temperature setpoint.
This sequence requires a room temperature sensor.
Heating -
When the room requires heating,
the controller will reset the supply air temperature
setpoint up to the maximum (90°F) while increasing
the supply fan speed up to its maximum heating
speed.
Cooling -
When the room requires cooling, the
controller will first reset the supply air temperature
setpoint down to the minimum (55°F) while the
supply fan remains at the minimum cooling speed.
After a time delay, the supply fan speed will increase
up to its maximum cooling speed to maintain the
room temperature setpoint.
Exhaust Fan VFD Sequence
The factory installed VFD is wired to the controller.
Exhaust fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the exhaust fan speed.
•
Optional Building Static Pressure Sensor:
The
controller will modulate the exhaust fan based upon a
comparison of the building static pressure setpoint to
the actual building static pressure level reported from
the sensor.
•
Optional Supply Fan Tracking:
The controller will
proportionally modulate the exhaust fan based upon
the supply fan speed.
•
Optional Outdoor Air Damper Tracking:
The
controller will proportionally modulate the exhaust fan
based upon the outdoor air damper position.
Sequence of Operation
