Carrier RTU Open v5 Integration Manual page 39

The VVT Master gathers the following information from the slave zone controllers:

occupancy status

setpoints

zone temperature

relative humidity

CO level
2

damper position

optimal start data
The VVT Master performs mathematical calculations and algorithms on the data and then sends the composite
information to the air source. The VVT Master receives information from the air source such as System Mode,
Supply Air Temperature, and Outside Air Temperature (if available), and passes that information to all linked
controllers.
The RTU Open is capable of operating in an SAV (Staged Air Volume) mode that is ideally suited to VVT systems.
SAV requires the unit's fan be controlled by a VFD to provide variable speed fan operation. SAV operation is
standard on the Carrier 3-stage LC Weather Expert units but can also be used with other 2-stage heat/cool units.
To obtain SAV operation on those units, the Fan Control must be set to Variable Speed. In this mode, the fan runs
at the lowest speed possible, saving energy and preventing excessive air from being bypassed during heating or
cooling operation. Refer to the fan control and heating/cooling sequences for details on the specific operation.
Note that using variable speed fan control does NOT eliminate the need for a Bypass damper.
NOTE The following paragraphs describe the interaction between the air source (RTU Open) and its subordinate
zones. Additional information regarding Open Zoned Systems may be found in the VVT Zone and VVT Bypass
Controller Installation Guides.
The VVT Master determines system operation by prioritizing heating and cooling requirements from all the zones
based on their occupancy and demand. The VVT Master scans the system continuously to determine if any zones
are occupied. Occupied zones are a higher priority than unoccupied zones. The VVT Master evaluates all the
occupied zones' heating or cooling demands and sends a request to the air source (RTU Open) for:

Cooling, if the number of occupied zones with cooling demands exceeds the number of occupied zones with
heating demands, and the demand is greater than or equal to the number of configured Linkage Callers.

Heating, if the number of occupied zones with a heating demand exceeds or is equal to the number of
Linkage Callers.
If no zones are occupied or no occupied zones require heating or cooling, the VVT Master performs the evaluation
described above for the unoccupied zones.
The VVT Master then gathers the following information and sends it to the air source (RTU Open):

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 CO2 values (if applicable)
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 of the reference
zone 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 its
heat has failed, the air source's actual mode indicates that and it's current mode is sent to the zones so that they
can control accordingly.
RTU Open v5
Integration Guide
35
Sequence of Operation
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