MicroMetl ECD-SRTCA-D2 - Start-Up and Operation of the Economizer; Economizer Cooling Operation; Economizer Heating Operation

23
Since 1965
MicroMetl
Table 14 - Damper Position Control, 2-Speed Fan Motor, Economizer Cooling Not Available
INPUT VOLTAGE
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
SUPPLY FAN
MOTOR SPEED
OFF LOW LOW HIGH HIGH
DAMPER POSITION DAMPER POSITION
NO CO2 SENSOR CLOSED MIN POS-L MIN POS-L MIN POS-H MIN POS-H
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
START-UP AND OPERATION
Cooling with Economizer — For Occupied mode operation of
economizer, there 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 economizer control in Unoccupied mode.
See Table 14 for Damper Position Control.
During Occupied mode operation, indoor fan operation will be
accompanied by economizer dampers moving to Minimum Position
setpoint for ventilation. If indoor fan is o󰀨, 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, di󰀨erential
dry bulb or di󰀨erential 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 mixed air
temperature. Default mixed air 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 called for. The
economizer control will call for compressor operation. Dampers will
modulate to maintain MAT at set point concurrent with Compressor
1 operation. The “Low T Lock” setting (default 32°F) will lock out
compressor operation when outside air temperature is below
setpoint.
When space temperature demand is satised (thermostat Y1
opens), the dampers will return to Minimum Damper position if
indoor fan is running or fully closed if fan is o󰀨.
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 de-energized as
the dampers close below the EXH1 SET setpoint. (For single speed
unit.)
Damper movement from full closed to full open (or vice versa) will
take between 1 1/2 and 2 1/2 minutes.
Heating with 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 o󰀨, 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.