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Sequence of Operation
- Unoccupied cooling is enabled when the room
temperature is greater than the unoccupied
cooling set point plus differential (85°F±5°F).
The supply air temperature set point will be
set to the supply minimum reset limit (55°F).
The unit cycles off when the room temperature
reaches the unoccupied cooling set point minus
differential.
Set Point Control
Supply air temperature set point can either be reset
by outside air temperature, or room temperature. If
equipped with BMS communications, the user can
also directly set the supply temperature set point, or
room temperature set point (if equipped with a room
temp sensor).
•
Outdoor Air Temperature Reset Function:
Without a room temperature sensor, the controller
will default to supply temperature reset based
on outdoor air temperature. The controller will
monitor the OA temperature and reset the supply
temperature set point based upon the outdoor air
reset function.
• Room Temperature Reset (optional):
With a
room temperature sensor, the controller will
adjust the supply air temperature set point up/
down accordingly to satisfy the desired room
temperature. Cooling and heating are determined
by a difference in temperature of the room
temperature sensor compared to the desired room
temperature set point.
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 (70°F).
•
Indirect Gas Furnace:
DDC controller will
modulate the indirect gas furnace to maintain the
supply temperature set point.
•
Hot Water Coil:
DDC 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:
DDC controller will modulate an
electric heater to maintain the supply temperature
set point.
•
Heat Pump:
DDC controller will stage
compressor(s) to maintain the supply air set point.
This signal will come wired to the factory provided
heat pump module.
All external water valves and
valve controls are provided, wired and mounted
by others in the field, including freeze protection.
Cooling
The cooling is controlled to maintain the supply
temperature set point. The mechanical cooling will be
locked out when the outside air temperature is below
the cooling lockout (55°F).
•
Chilled Water:
DDC 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!
•
Packaged DX Cooling (Standard Scroll):
DDC
controller will control stages of cooling to maintain
the supply air set point.
•
Packaged DX Cooling (Digital Scroll):
DDC
controller will modulate the digital scroll to maintain
the supply air temperature set point.
•
Heat Pump:
DDC controller will power the
reversing valve within the heat pump module
to direct the refrigerant flow for airside cooling.
The cooling is controlled to maintain the supply
temperature set point.
All external water valves
and valve controls are provided, wired and
mounted by others in the field, including freeze
protection.
Dehumidification
The cooling is controlled to maintain the cold coil set
point. The Dehumidification sequence will be locked
out when the OA is less than the dehumidification
lockout (10°F) above the cold coil set point.
•
Optional Room Dehumidistat:
The room
dehumidistat is a field mounted sensor that
monitors the relative humidity (RH) of the room.
If the RH exceeds set point, the dehumidistat will
decrease the cold coil set point to the dehumidify
set point (50°F) to further dry the supply air.
Once the room dehumidistat is satisfied, the DDC
controller will resume normal operation.
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.
•
Primary Heating Source:
The main heating source
is enabled to reheat the air to meet the supply
temperature set point. (Except heat pump).
•
Modulating Hot Gas Reheat (bypass damper):
The
DDC controller will open the On/Off hot gas reheat
valve, and modulate the Hot Gas Reheat bypass
damper to maintain the supply temperature set
point.
•
Modulating Hot Gas Reheat (valve):
The DDC
controller will modulate the hot gas reheat valve to
maintain the supply temperature set point.
•
On/Off Hot Gas Reheat:
The DDC controller will
open the On/Off hot gas reheat valve to maintain
the supply temperature set point.
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DDC Controller for Tempered Air Products
®
