Greenheck Microprocessor Controller (475595 IOM) TAP v2.10 April 2014 (RVE, ERCH-01, ERT-01) - Manual (Page 4)

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 set point 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 set point. If equipped
with an energy wheel, see Energy Recovery Wheel
Sequence.
• Temperature: The economizer will be locked out
when:
- The outside air is less than the economizer low
lockout (40°F).
- 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/Dew Point: The economizer will be
locked out when:
- The outside air is less than the economizer low
lockout (40°F dry-bulb).
- The outside air is greater than the economizer
high lockout (75°F dry-bulb).
- The outside air is greater than the economizer
high dew point lockout (55°F dew point)
- The unit is operating in dehumidification mode.
- There is a call for heating.
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. If equipped with
BMS communications, the user can also directly set the
cold coil leaving air 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 reset the
cold coil set point to the minimum (50°F). Once the
room dehumidistat is satisfied, the cold coil set point
will return to the maximum (55°F).
• Optional Room Relative Humidity Sensor: The
controller will adjust the cold coil leaving air
temperature set point between the minimum (50°F)
and maximum (55°F) set points, to satisfy the desired
room relative humidity set point.
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). The
primary heat source may also be configured to act as
secondary reheat.
• Modulating Hot Gas Reheat (bypass damper): The
microprocessor 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
microprocessor controller will modulate the hot gas
reheat valve to maintain the supply temperature set
point.
• On/Off Hot Gas Reheat: The microprocessor
controller will open the On/Off hot gas reheat valve to
maintain the supply temperature set point.
Supply Fan VFD Sequence
If the factory has installed a VFD and wired it to the
controller, it is intended to operate at a constant speed
during operation. This 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 Room CO2 Sensor: The controller will
modulate the supply fan based upon a comparison
of the CO2 set point to the actual CO2 levels
reported from the sensor. Mechanical high static
protection cutoffs must be installed by others
to protect the system and equipment from
over-pressurization.
• Optional Duct Static Pressure Sensor: The
controller will modulate the supply fan based upon a
comparison of the duct static pressure set point to
the actual duct static pressure level reported from
the sensor. Mechanical high static protection
cutoffs must be installed by others to protect
the system and equipment from over-
pressurization. The manufacturer does not
assume responsibility for this.
• Optional Building Static Pressure Sensor: The
controller will modulate the supply fan based upon a
comparison of the building static pressure set point
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 set point.
This sequence requires a room temperature sensor.
Heating - When the room requires heating, the
controller will reset the supply air temperature set
point 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
set point 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 set point.
4 DDC Controller for Tempered Air Products
®