Greenheck IG / IGX (464104 IOM) (Pre-2009) - Manual (Page 59)

59
Operation - Economizer
NOTE!
Only models IG-HV and IGX-HV with options EC-1, 2, 3 or 4 use an 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
55ºF, the economizer sends the dampers to the 100% outside air position. If the outside air is less than 55ºF, the
economizer modulates the dampers to achieve a 55ºF 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 55ºF 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 factory installed in the discharge of the unit. A third dry bulb temperature sensor is field
installed in the return air duct.
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 55ºF mixed air temperature. If
the outside air temperature is less than the return air temperature, but a 55ºF 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 factory
installed in the return air duct. A dry bulb temperature sensor is field 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 55ºF mixed air temperature. If the outside enthalpy is less
than the return air temperature, but a 55ºF mixed air temperature cannot be achieved, the programmable room
thermostat may call for mechanical cooling.
Operation