21
Model RT Energy Recovery Unit
Microprocessor Controller
Sequence of Operation
Microprocessor Controller
This unit is typically provided with a microprocessor
controller (called a DDC) that is factory programmed,
mounted and tested. The controller has an LCD
screen to provide for easy monitoring of unit
operation and changing set points. Factory-installed
sensors are already mounted and wired, but there
are several optional sensors and control devices that
must be field-installed. See also the unit-specific
wiring diagram and the manual supplied with the
microprocessor controller.
Unit Start Command:
• Factory mounted and wired Outdoor air (D1) and
Exhaust air (D2) damper actuators are powered.
• Exhaust fan starts after a 10-second delay
(adjustable).
• Supply fan starts 5 seconds (adjustable) after the
exhaust fan.
• Heating, cooling and wheel operation per below.
Unit Stop Command (or De-Energized):
• Supply fan, exhaust fan, tempering options and
wheel are de-energized.
• Outdoor Air and Exhaust Air damper actuators are
de-energized and dampers will close.
Remote On / Off
Unit DDC shall have an input allowing the unit to be
started/stopped by others.
Occupied / Unoccupied Modes
Shall be based on a 7-day time clock internal to the
controller. The schedule shall be set by the end user.
When a user initiates an override input, the DDC
would switch from unoccupied to occupied mode.
The DDC will return to the scheduled occupied/
unoccupied mode after the override time has expired
(60 min, adjustable). If internal time clock is disabled,
a remote contact or a BMS can control the occupied/
unoccupied mode.
•
Occupied Mode
1. Supply fan ON.
2. Exhaust fan ON.
3. Heating per below.
4. Cooling per below.
5. Wheel control per below.
•
Unoccupied Mode (Unit Off
)
Default setting when there is no recirculation
damper or room temperature sensor
• Unoccupied mode (Cycle on Room)
Optional unoccupied mode when there is a
recirculation damper and a room temperature
sensor wired to unit.
1. Exhaust fan off
2. Supply fan off
3. Recirculation air damper open.
4. OA Damper Closed
5. On a call for heating (room temp set point
– differential, 65°F - 5°F = 60°F) supply fan
cycles on, and the heating increases the
room temperature. Unit cycles off when room
temperature reaches the unoccupied set
point (65°F, adjustable).
6. On a call for cooling (room temp set point
+ differential, 85°F + 5°F = 90°F) supply fan
cycles on, and the cooling decreases the
room temperature. Unit cycles off when room
temperature reaches the unoccupied set
point (85°F, adjustable)
Cooling Sequence
DDC 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. The mechanical cooling
will be locked out when the outside air is < 55°F - 2°F
hysteresis, adjustable.
•
Water Source Heat Pump Cooling:
DDC will
provide a digital signal for 1 or 2 stages of
cooling to maintain the supply air set point
(adj.). This signal will come wired to the factory
provided condensing section.
Dehumidification Sequence
DDC will power the reversing within the heat pump
module to direct the refrigerant flow for airside
cooling. The cooling is controlled to maintain the
cooling-coil set point. The dehumidification sequence
will be locked out when the OA is <10°F above the
cold-coil set point. The mechanical cooling will
be locked out when the outside air is < 55°F - 2°F
hysteresis, adjustable.
•
Water Source Heat Pump Cooling:
DDC will
provide a digital signal for 1 or 2 stages of
cooling to maintain the supply air set point
(adj.). This signal will come wired to the factory
provided heat pump module.
Reheat Sequence
While the unit is in dehumidification mode, the
outdoor air can be reheated via Modulating Hot Gas
Reheat for space neutral applications.
•
Modulating Hot Gas Reheat:
The controller will
send a 0-10 V signal to the modulating hot gas
reheat valve to maintain the supply temperature
set point (adjustable).
