Operation:
For economic reasons, the Airside Economizer is the first stage of cooling, followed by
Chilled Water cooling (if used) and then DX cooling. When this feature is enabled, the
temperature being controlled will be defaulted to the Discharge Air. Many conditions
must be monitored to determine if the damper can open. If so, the energy saver icon is
displayed on the home screen along with the percentage of damper opening. While in
the Energy Saver mode, the setpoint for DX cooling is pushed up 1.3°F to allow room
for the energy saver to work.
To maximize energy efficiency, DX assisted cooling (or CW cooling if used) does not
begin until the outside air damper is fully open for the entire duration of the “DX Assist
Delay”. When DX or CW is assisting with cooling, the damper will be fully open. After
DX cooling is no longer assisting, the damper will remain fully open for the “DX -> ES
Delay” time before, the damper will return to normal temperature modulation. The DX ->
ES Delay time cycle will be terminated if the temperature drops more than 5°F below
setpoint. Please refer to the section “Operation of DX Cooling” for information regarding
when the compressors will run in the energy saver mode.
Economizer Modes:
Fixed Dry Bulb – Outside air must be below the OAT Temp setting.
Differential Dry Bulb - Outside air must be below the inside return air temperature.
Notice: The Dry Bulb modes listed above should not be selected in applications
requiring controlled humidity.
Fixed Enthalpy – Same as Fixed Dry bulb but also requires that the outside air
enthalpy be below the Hi Enthalpy setpoint.
Differential Enthalpy - Same as Differential Dry bulb but also requires that the
outside air enthalpy be below the inside air enthalpy.
Damper modulation: Damper position is controlled by a P+I algorithm (set in factory
settings menu) to maintain the temperature setpoint. The temperature band for the
algorithm is dynamically increased as the outside air temperature drops. Therefore, for
the same discharge temperature error, damper modulation will be diminished under
lower outside air temperatures. The band for damper modulation is increased by 1
degree for every 5 degrees that the Outside Air Temperature is below the temperature
setpoint.
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