Carrier VVT Zone II Installation And Startup Manual page 57

The VVT Master then gathers the following information and sends it to the air source:
• The setpoints and zone temperature from the zone with the greatest demand for the requested air source
mode (heating or cooling). (This zone is called the reference zone.)
•
The system occupancy status
•
Most open damper position from any zone
•
RH and CO
The air source responds by sending the air source mode, supply air temperature, and outside air temperature. The
air source verifies the mode by comparing its supply air temperature to the space temperature received through
Linkage. See the air source documentation for operation and parameters used to verify its mode. This verification
allows the VVT system to determine if the desired air source mode is actually being provided. For example, if the
VVT Master sends a request for heating and the air source does not have heat or it's heat has failed, the air
source's actual mode indicates that and its current mode is sent to the zones so that they can control accordingly.
The system remains in that mode until all zones of that demand are satisfied or until the System Mode Reselect
Timer (factory default is 30 minutes) causes a forced re-evaluation of the system. If there is no demand for the
opposite mode, the reselect timer starts again and the current mode continues until all zones are satisfied or until
the reselect timer expires, repeating the process. If there is a demand for the opposite mode, the VVT Master
sends the reference zone's space temperature and setpoints to the air source and restarts the reselect timer. The
air source re-evaluates its demand based on the new information and goes to the Vent mode until the new mode
can be verified as described above. The amount of time this takes is determined by the air source's operating
parameters.
The VVT Master continuously evaluates the system and updates the air source with the most current system
demand. Based on the evaluation, the reference zone can change from one zone to another. The evaluation
process continues until there is no demand from any zone or the 30 minute timer causes a re-evaluation of the
system conditions.
If no heating or cooling is required or the current air source mode is satisfied, the VVT Master calculates the
weighted average of the occupied and unoccupied heating and cooling setpoints. It also calculates a zone
temperature that is midway between the setpoints (occupied or unoccupied based on the system's current
occupancy status). This information, plus the occupancy status, is sent to the air source so that its current mode is
disabled and the unit ceases heating or cooling operation. If the system is occupied, the air source fan and OA
damper, if applicable, operate to maintain proper ventilation.
VVT Zone II Controller
Installation and Start-up Guide
values (if applicable)
2
53
Sequence of operation
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