Microprocessor Controller for DOAS
4
Sequence of Operation
Sequence of Operation
-
Night Setback:
Unoccupied mode when there
is space temperature and/or humidity sensor(s)
connected to the controller. The unit will cycle
on to maintain unoccupied space set points if
there is a call for unoccupied heating, cooling or
dehumidification.
º Exhaust fan off, if equipped
º Supply fan on
º Recirculation air damper open
º OA damper closed
º Tempering operations begin
Set Point Control (Occupied)
Supply air temperature set point can be configured
as constant, or can be reset by either outside air
temperature, or space temperature set point. If
equipped with BMS communications, the user can
also directly command the temperature set point, if
equipped.
•
Outside Air Temperature Reset Function:
The
controller will default to supply temperature reset
based on OA temperature. The controller will monitor
the OA temperature and reset the supply temperature
set point based upon the OA reset function.
• Space temperature Reset:
With a space
temperature sensor, the controller will adjust the
supply air temperature set point between the min
(55°F) and max (90°F), to satisfy the desired space
temperature. The temperature set point can be
adjusted locally at the microprocessor, the BMS or a
space thermostat.
Set Point Control (Unoccupied)
When equipped with an unoccupied recirculation
damper and optional space temperature and/or
humidity sensors, the unit will cycle on to maintain the
unoccupied space set points.
•
Unoccupied Heating:
If equipped with heating,
the unit is enabled when the space temperature is
less than the unoccupied heating set point minus
differential (60°F). The supply air temperature set
point will be set to the supply max reset limit (90°F).
The unit cycles off when the space temperature
reaches the unoccupied heating set point.
• Unoccupied Cooling:
If equipped with cooling,
the unit is enabled when the space temperature is
greater than the unoccupied cooling set point plus
differential (80°F+5°F). The supply air temperature set
point will be set to the supply min reset limit (55°F).
The unit cycles off when the space temperature
reaches the unoccupied cooling set point.
• Unoccupied Dehumidification:
If equipped with
cooling, the unit is enabled when the space relative
humidity exceeds the unoccupied space relative
humidity set point plus differential (50%+5%). The
supply air temperature set point will be set to the
equivalent occupied supply set point.
• Morning Warm-Up/Cool Down:
At the request to
occupy the space, the unit will run using the warm-
up or cool down sequence until the occupied set
point is achieved. The heating or cooling mode
must not be locked out and the space temperature
is below or above set point by the unoccupied
hysteresis (5°F, adj). This optional sequence requires
a space temperature sensor and is field-enabled.
The following steps occur during a morning warm-
up/cool down:
- The dampers would be in full recirc if the damper
actuators are not powered (adj) during occupied
mode. Otherwise the following is true:
• Outside air damper is open to minimum OAD
position.
• Recirculation air damper is open at 100% minus
OAD position.
-
Supply Fan is ON at 100%.
- Exhaust fan is OFF.
- In heating, controls to maintain the maximum
supply set point (90ºF).
-
In cooling, controls to the minimum supply set
point (50ºF).
-
Reheat off.
- Energy recovery wheel off.
Heating
The heating is controlled to maintain the supply
temperature set point. The heating will be locked out
when the outside air temperature is above the heating
lockout (80°F adj).
•
Indirect Gas Furnace:
Microprocessor controller will
modulate the indirect gas furnace to maintain the
supply temperature set point.
•
Hot Water Coil:
Microprocessor controller will
modulate a hot water valve (provided by others)
to maintain the supply temperature set point.
Coil
freeze protection must be provided by others in
the field!
•
Electric Heater:
Microprocessor controller will
modulate an electric heater to maintain the supply
temperature set point.
Cooling
The cooling is controlled to maintain the supply
temperature set point. The cooling will be locked out
when the outside air temperature is below the cooling
lockout (55°F).
•
Chilled Water:
Microprocessor controller will
modulate a chilled water valve (provided by others)
to maintain supply air set point. Coil freeze protection
must be provided by others in the field!
•
Mechanical Cooling:
Microprocessor controller
enables stages of cooling to maintain the supply air