6
ADJUSTABLE OUTDOOR DRY BULB CHANGEOVER
(-DWDS
Models) —
For this control mode, the outdoor temperature is compared
to a selectable set point on the OAT sensor. If the outdoor air temperature
is above the set point, the
economizer will adjust the outdoor air
dampers to minimum position. If the outdoor air temperature is below
the set point, the position of the outdoor air dampers will be controlled
to provide free cooling using outdoor air. When in this mode, the Free
Cool LED next to the outdoor enthalpy set point (ABCD) potentiometer
will be on. The changeover temperature set point is controlled by the dip
switches on the sensor. See Fig. 12 for the switch positions corresponding
to the temperature changeover values. The ABCD potentiometer on the
controller should be turned fully clockwise (CW) to the “D” position.
OUTDOOR ENTHALPY CHANGEOVER (-DWES Models)
—
When the outdoor air enthalpy rises above the outdoor enthalpy
changeover set point, the outdoor-air damper moves to its minimum
position The outdoor enthalpy changeover set point is set with the outdoor
enthalpy set point (ABCD) potentiometer on the
economizer controller.
The set points are A, B, C, and D (See Figs. 11, 14 and 15). The factory-
installed 620-ohm jumper must be in place across terminals SR and SR+
on economizer controller. (See Fig. 7). When not using CO2 sensors, set
the DCV Max potentiometer to completely closed (CCW) to insure that
the Minimum Position potentiometer functions correctly.
DIFFERENTIAL ENTHALPY CONTROL (-DWZS Models)
— For
differential
enthalpy control, the
economizer controller uses two enthalpy
sensors, 9901-0018 in the outside air and 9901-0018 in the return
airstream. The economizer controller compares the outdoor air enthalpy
to the return air enthalpy to determine economizer damper position. The
controller selects the lower enthalpy air (return or outdoor) for cooling.
For example, when the outdoor air has a lower enthalpy than the return
air, the
economizer opens to bring in outdoor air for free cooling. Mount
the return air enthalpy sensor in the return air duct. (See Fig. 7 and 13)
When using this mode of changeover control, turn the outdoor enthalpy
set point (ABCD) potentiometer fully clockwise to the D setting.
POWER EXHAUST SET POINT ADJUSTMENT
—If the optional
power exhaust accessory is installed, the exhaust set point will determine
when the power exhaust fan runs based on damper position. The set point
is modified with the Exhaust Fan Set Point (EXH SET) potentiometer.
(See Fig. 11) The set point represents the damper position above which
the exhaust fans will be turned on. When there is a call for exhaust, the
economizer
controller provides a 45 ± 15 second delay before exhaust
fan activation to allow the dampers to open. This delay allows the damper
to reach the appropriate position to avoid unnecessary fan overload.
Fig. 13 - Differential Return Air Enthalpy Sensor
Mounting Location
Fig. 12 - Outdoor Air Temperature
Changeover Set Points
Economizer
Economizer
Controller
Grommet
Differential
Enthalpy Sensor
Return Duct
(Field-Provided)
CAUTION
EQUIPMENT DAMAGE HAZARD
Failure to follow this caution may result in damage to equipment.
If a separate field-supplied transformer is used to power the IAQ
sensor, the sensor must not be grounded or the
economizer control
board will be damaged.
!
FIXED DRY BULB OUTDOOR AIR TEMPERATURE SENSOR
(-DWFS Models)
— For this control mode the, the outside air
temperature is compared to the fixed temperature on the OA sensor,
which is 70 degrees.
If the outside air temperature is above 70 degrees F, the economizer
will adjust the outdoor dampers to minimum position. If the outdoor air
temperature is below 70 degrees, the position of the outside air damper
will be controlled to provide free-cooling using outside air.
When in the free-cooling mode, the Free Cooling LED next to the
enthalpy potentiometer will be on. The ABCD potentiometer on the
controller should be adjusted to the “D” position.
