This function exists to execute group data exchanged between room applications and primary system applications. It communicates with the primary system using standard BACnet objects. There are two ways data can be shared between the primary system and the rooms. These are:
- Read / write to standard BACnet Objects in individual automation stations.
- Each Central function AF includes Group master objects that link to the Group member objects in the room applications. Central function AF's are available from the library for download to an automation station.
See ABT Site Help, under Building > Central functions for more information on grouping.
Common uses for Group master / Group member functionality are Scheduling and Duct pressure reset. See the following sections for additional information.
Start/Stop on Demand from Zones
When the schedules apply to rooms, rather than equipment, a single schedule may apply to one or more rooms. The rooms served by one HVAC supply system can be driven by any number of schedules. Interactions between the scheduler and the room control application affect room operating mode demands for HVAC.
Rooms scheduled to run in the Economy or Standby mode, switch to Comfort on input from occupancy sensors or a room unit. The room may call on primary plants to run and stop in response to this unscheduled use
Maintain Economy Conditions
Rooms operating in the Economy mode may need primary heating or cooling equipment to run intermittently in order to maintain the economy setpoints. The rooms send signals to indicate the demand for heating and cooling.
Duct pressure reset
Energy codes (for example, ASHRAE 90.1) in the US require controls that result in at least one damper nearly fully open’ but do not require a specific algorithm. The air handler adjusts fan speed and duct pressure to the lowest level that satisfies air demands from the zones.
The VAV and FPB application templates support a variety of approaches to duct pressure reset. For example the saturation level parameter (StrtnLvl) can be adjusted to increase/decrease the terminal box's sensitivity to a saturation condition. The group master object for supply air coordination collects data from several supply air group members to support duct pressure reset. See the section Supply Airflow PID Controller for additional information.