17
OPERATION
Cooling, Unit with Ultra Low Leak Economizer
For Occupied mode operation of Ultra Low Leak Economizer, here
must be a 24-v signal at terminals R and OCC (provided through
PL6-3 from the unit’s IFC coil). Removing the signal at OCC places
the Ultra Low Leak Economizer control in Unoccupied mode.
During Occupied mode operation, indoor fan operation will be
accompanied by economizer dampers moving to Minimum Position
setpoint for ventilation. If indoor fan is off, dampers will close.
During Unoccupied mode operation, dampers will remain closed
unless a Cooling (by free cooling) or DCV demand is received.
When free cooling using outside air is not available, the unit cooling
sequence will be controlled directly by the space thermostat.
Outside air damper position will be closed or Minimum Position as
determined by Occupancy mode and fan signal.
When free cooling is available as determined by the appropriate
changeover command (dry bulb, outdoor enthalpy, differential
dry bulb or differential enthalpy), a call for cooling (Y1 closes at
the thermostat) will cause the economizer control to modulate
the dampers open and closed to maintain the unit supply air
temperature. Default supply temperature is 53°F, with a range of
38°F to 70°F. Compressor will not run.
Should 100% outside air not be capable of satisfying the space
temperature, space temperature will rise until Y2 is closed. The
economizer control will call for compressor operation. Dampers will
modulate to maintain SAT at setpoint concurrent with Compressor
1 operation. The “Low T Temp” setting (default 32°F) will lock out
compressor operation.
When space temperature demand is satised (thermostat Y1
opens), the dampers will return to Minimum Damper position if
indoor fan is running or fully closed if fan is off.
If accessory power exhaust is installed, the power exhaust fan
motors will be energized by the economizer control as the dampers
open above the EXH1 SET setpoint and will be-energized as the
dampers close below the EXH1 SET setpoint.
Damper movement from full closed to full open (or vice versa) will
take between 1-1/2 and 2-1/2 minutes.
Heating with Ultra Low Leak Economizer
During Occupied mode operation, indoor fan operation will be
accompanied by economizer dampers moving to Minimum Position
setpoint for ventilation. If indoor fan is off, dampers will close.
During Unoccupied mode operation, dampers will remain closed
unless a DCV demand is received.
When the room temperature calls for heat (W1 closes), the heating
controls are energized.
Demand Controlled Ventilation
If a eld-installed CO
2
sensor is connected to the Ultra Low Leak
Economizer control, a Demand controlled Ventilation strategy will
operate automatically. As the CO
2
level in the space increases
above the setpoint, the minimum position of the dampers will be
increased proportionally, until the Maximum Ventilation setting is
reached. As the space CO
2
level decreases because of the increase
in fresh air, the outdoor damper will follow the higher demand
condition from the DCV mode or from the free cooling mode.
DCV operation is available in Occupied and Unoccupied periods
with Ultra Low Leak Economizer. However, a control modication
will be required on the units to implement the Unoccupied period
function.
Table 10 - Damper Position Control, 2-Speed Fan Motor, Economizer Cooling Not Available
INPUT
OCC 0 - V 24 - V 24 - V 24 - V 24 - V
Y1 0 - V 0 - V 24 - V 24 - V 0 - V
Y2 0 - V 0 - V 0 - V 24 - V 0 - V
W1 0 - V 0 - V 0 - V 0 - V 24 - V
SUPPLY FAN
MOTOR SPEED
OFF LOW LOW HIGH HIGH
DAMPER POSITION
NO CI2 SENSOR CLOSED MIN POS MIN POS MIN POS MIN POS
W/ CO2 SENSOR CLOSED
FROM
VENTMIN L
TO
VENTMAX L
FROM
VENTMIN L
TO
VENTMAX L
FROM
VENTMIN H
TO
VENTMAX H
FROM
VENTMIN H
TO
VENTMAX H
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