This selection loads logic that reduces the intake of outdoor air when the temperature is low. This reduction is accomplished by closing dampers, reducing the volume differential (if Variable Capacity Return Fan Volume Matching control is selected), and turning off or closing two-position fans or dampers.
If a preheat coil is located downstream of the mixing plenum (that is, it is in the mixed air), the Preheat Temperature (downstream of the coil) serves as the process variable for this control strategy. Otherwise, the Mixed Air Temperature serves as the process variable.
The control logic for the low limit strategy is embedded directly into the Output Control modules and activated simply by connecting the appropriate setpoint and process variable. The logic takes precedence over all logic other than Emergency Modes.
This selection is allowed if any of the Economizer Damper, Minimum Outdoor Air Fan, or Minimum Outdoor Air Damper options is selected.