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NOTE
Only models IG-HV and IGX-HV with options EC-1,
2, 3 or 4 use an economizer.
Operation - Economizer
Option EC-1
(Outside Air Temperature Reference)
This option uses one dry bulb temperature sensor
field-installed in the inlet of the unit. A second dry
bulb temperature sensor is factory-installed in the
discharge of the unit.
After a call for cooling, the outside air temperature is
compared to the economizer set point. If the outside
air temperature is above the economizer set point,
the economizer sends the dampers to the minimum
outside air position and calls for mechanical cooling. If
the outside air temperature is between the economizer
set point and 55
°
F, the economizer sends the dampers
to the 100% outside air position. If the outside air
is less than 55
°
F, the economizer modulates the
dampers to achieve a 55
°
F mixed air temperature.
Option EC-2
(Outside Air Enthalpy Reference)
This option uses one enthalpy sensor field-installed in
the inlet of the unit. A dry bulb temperature sensor is
installed in the discharge of the unit.
After a call for cooling, the outside air enthalpy is
compared to the field-adjustable enthalpy changeover
set point. If the outside air enthalpy is less than the
set point, the dampers will modulate to provide a 55
°
F
mixed air temperature. If the outside air enthalpy is
greater than the set point, the economizer sends the
damper to the minimum outside air position and sends
a call for mechanical cooling.
Option EC-3
(Differential Temperature Control)
This option uses one dry bulb temperature sensor
field-installed in the inlet of the unit. A second dry bulb
temperature sensor is field-installed in the return air
duct. A third dry bulb temperature sensor is factory-
installed in the discharge of the unit.
After a call for cooling the economizer compares the
outdoor and return air temperatures. If the outdoor
air temperature is greater than the return air dry bulb
temperature, the economizer sends the dampers to
the minimum outside air position and sends a call for
mechanical cooling. If the outside air temperature is
less than the return air temperature, the economizer
will modulate the dampers to achieve a 55
°
F mixed
air temperature. If the outside air temperature is less
than the return air temperature, but a 55
°
F mixed air
temperature cannot be achieved, the programmable
room thermostat may call for mechanical cooling.
Option EC-4
(Differential Enthalpy Control)
This option uses one enthalpy sensor, field-installed in
the inlet of the unit. A second enthalpy sensor is field-
installed in the return air duct. A dry bulb temperature
sensor is factory-installed in the discharge of the unit.
After a call for cooling the economizer compares
the outdoor and return air enthalpies. If the outdoor
air enthalpy is greater than the return air enthalpy,
the economizer sends the dampers to the minimum
outside air position and sends a call for mechanical
cooling. If the outside enthalpy is less than the
return air enthalpy, the economizer will modulate the
dampers to achieve a 55
°
F mixed air temperature.
If the outside enthalpy is less than the return air
temperature, but a 55
°
F mixed air temperature cannot
be achieved, the programmable room thermostat may
call for mechanical cooling.
®
Model IG / IGX Make-Up Air