OAD and RAD Proportional - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 16.0

Controller Tool Help

Johnson Controls
Product name
Controller Configuration Tool
Document type
User Guide
Document number
Revision date
Note: This is the only option available for Variable Speed Relief Fan (Bldg Static Press Control).

Select this option to control the Outdoor and Return Air Dampers only. In this control scheme, the exhaust damper is completely open while the outdoor and return dampers are modulated to control air movement to the mixing box and thus, limit the intake of fresh air. Also, this control scheme is unique in that the command to the damper is twice the amount of air requested. For example, if you require 20% fresh air, the outdoor air damper command is 40% to achieve 20% flow while the return damper remains fully opened. This sequence is done in accordance with ASHRAE standards to minimize the resistance to airflow and reduce fan energy.

Per ASHRAE Guideline16-2003 - Selecting Outdoor, Return, and Relief Dampers for Air-Side Economizer Systems, OAD & RAD Proportional with Separate Outputs is required if Variable Speed Relief Fan (Building Static Press Control) is selected.

The OAD & RAD Proportional options can only be selected if Variable Speed Return Fan Volume Matching is selected.

  • Separate Outputs adds two AOs (OAD-O and RAD-O) for the damper signals.
  • Optimized Dampers (G36) sequences the OAD-O and RAD-O dampers as part of the discharge air temperature (DAT) control loop prior to use of any cooling coil. If additional cooling is required, the OAD-O damper opens first and then the RAD-O damper shuts. If free cooling is unavailable, minimum ventilation is maintained by the minimum outdoor airflow loop setting both a minimum OAD-O position and a maximum RAD-O position.
  • Common Output adds a single AO (MAD-O) to control both dampers.
  • Two Position EAD optionally adds a single BO to open the exhaust air damper when the unit is occupied and close it when it is unoccupied.