Free Cooling is Available - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 13.1

The Free Cooling is Available logic block provides economizer decision logic to determine when outdoor air, in excess of the minimum amount required for ventilation, can be used to reduce the cooling coil load.

The output is evaluated when the Supply Fan Status input changes and then subsequently only on its Interval (configurable property in the Advanced Details dialog box). This block does not constantly calculate its outputs as the inputs change.

Different methods include:

• Dry Bulb Temperature Economizer where if the supply fan is running and the Outside Air Temp is less than the Change Over Temp, then Free Cooling Available is True.

• Temperature and Enthalpy Economizer where measurements of Outside Air Temp, Outside Air Humidity, Return Air Temp, and Return Air Humidity are used to calculate the enthalpy of the outside air and return air streams. Free Cooling Available is True when:

  • the supply fan is running

  • the calculated outside air enthalpy is less than the calculated return air enthalpy

  • the outside air dry bulb temperature is less than the return air dry bulb temperature

• Model Based Economizer where measurements of Outside Air Temp, Outside Air Humidity, Return Air Temp, and Return Air Humidity as well as an estimate of the temperature leaving the cooling coil are used for calculations.

The following table describes the inputs and outputs of the Free Cooling is Available logic block.