36
FORM 145.32-IOM5
ISSUE DATE: 04/08/2019
SECTION 1 – INSTALLATION
AIRSIDE ECONOMIZER (ASE)
Optional airside economizer mixing box is designed
to attach to the return air (RA) side of the evaporator.
Mixing comes with low-leakage opposed blade damp-
ers. The economizer is used to provide ventilation and
free cooling for the DSH series of horizontal air handlers.
The economizer is setup through the LCD keypad dis-
play and joystick located on the unit SE control (SEC)
board or through a recommended mobile access portal
(MAP) gateway, available for purchase from the fac-
tory–see Mobile Access Portal Gateway Product Bul-
letin (
LIT-12011884
). The control board is mounted
inside of the unit main electrical box. Access to the
mixing box is not required to setup ASE sequence of
operation. Communication between SEC board and
ASE board automatically establishes through an SA
bus connection.
The factory supplied economizer includes: economizer
module, mixing box, actuator, enthalpy sensor,
temperature sensor, dampers, and wiring harness.
See
for the economizer
electrical wiring schematics or Airside Economizer Kit
Installation and Operation Instructions (
Form 145.10-
NO2
) for more details on installation and application.
Sequences of Operation
Several functions can drive the economizer, including
minimum position, free cooling, economizer loading,
and minimum outdoor air supply.
Economizer Minimum Position
The outside air (OA) damper minimum position is set
during occupied mode when outside air (OA) is not
suitable for free cooling and the unit is in economizer
mode. The position of the damper is set proportion-
ally between the Economizer Minimum Position and
the Economizer Minimum Position Low Speed Fan
setpoints in relation to the VFD output percentage.
On a constant volume single speed supply
fan system, both setpoints should be set to
the same value.
Free Cooling
Four types of free cooling options are available: dry
bulb changeover, single enthalpy, dual enthalpy
changeover, and auto.
Dry Bulb Changeover –
For dry bulb economizer op-
eration, the outside air is suitable for free cooling if
the outside air temperature (OAT) is 1.0°F below the
Economizer OAT Enable setpoint and 1.0°F below the
RA temperature (RAT). Free cooling is no longer avail-
able if the OAT rises above either the Economizer OAT
Enable setpoint or the RAT.
Single/Dual Enthalpy Changeover –
For single en-
thalpy economizer operation, the outside air is suitable for
free cooling if the OA enthalpy is at least 1 Btu/lb below
the economizer OA enthalpy setpoint and the OAT is no
greater than the RAT plus 9.0°F.
If the OAT rises above the RAT plus 10.0°F, free cool-
ing is no longer available. The OAT must drop to no
greater than RAT plus 9.0°F to enter free cooling again.
Free cooling is no longer available if the OA enthalpy
rises above the economizer OA enthalpy setpoint. For
dual enthalpy economizer operation, the OA enthalpy
must be lower than the RA enthalpy by 1 Btu/lb and the
OAT is no greater than the RAT plus 9.0°F.
Auto –
The control determines the type of free cooling
changeover based on which sensors are present and
reliable. Conditions include:
• Return and outside air dry bulb = dry bulb change-
over
• Return and outside air dry bulb and outside air hu-
midity = single enthalpy
• Return and outside air dry bulb and return and
outside air humidity = dual enthalpy
• If either the return or outside air dry bulb sensors
are unreliable, free cooling is not available
For more detailed installation and operation instructions,
refer to Airside Economizer Kit (
Form 145.10-NO2
).
