VVT sequence of operation - EasyIO - LIT-12014127 - EASYIO-FW-VAV - FV-VAV - 1.0

EasyIO FW-VAV Application Note

Brand
EasyIO
Product name
FV-VAV
Document type
Application Note
Document number
LIT-12014127
Version
1.0
Revision date
2024-04-09
Product status
Active
Language
English
Mode control

Place the system temperature set points in the occupied or unoccupied mode of operation in the VVT RTU or AHU controller occupancy schedule. Before scheduled occupied periods, the VVT RTU or AHU starts and provides morning heating and or cooling to allow the VAVs to precondition the space to ensure the occupied set point is achieved at the scheduled occupied time. A morning heating command from the VAV AHU/RTU forces the VAV to maximum flow and allows the VVT RTU or AHU to precondition the space when heating is required.

During unoccupied periods, the VVT RTU or AHU provides heating or cooling accordingly to allow the VVT zones to satisfy the unoccupied temperature set points.

During unoccupied and standby periods and subject to VVT RTU or AHU unit mode of operation, the VVT zone modulates in response to heating and cooling demands accordingly, to satisfy the unoccupied and standby temperature set points. Use the standby mode of operation for periods of temporary vacancy. You can determine the standby mode temperature set points. These set points are triggered by a local, hardwired occupancy motion sensor or by the network motion detection command from smart lighting control systems, communicating motion sensors, card access systems, global load shed commands, or other energy management systems (EMS) commands. The system reverts automatically to the correct mode of operation when power is restored after a power failure.

Occupant schedule override control

During the unoccupied mode, you can use the room temperature sensor wall module override button to place the system in the occupied mode for 120 minutes. The EMS front end monitors the VVT zones and returns the VVT RTU or AHU to the occupied mode of operation anytime you place a VVT zone in the override mode.

Temperature control

The application uses a PID algorithm for all modulating control. The VVT RTU or AHU discharge air temperature is monitored by the VVT zone damper controller through the direct digital controller (DDC) network and is used by the VVT zone damper controller to control the VVT zone damper control logic in a heating action (RA) or cooling action (DA) based on the current VVT RTU or AHU unit mode of operation.

When the VVT RTU or AHU provides cooling and the VVT zone requires cooling, the VVT zone damper modulates between an adjustable minimum and maximum damper position to satisfy the zone cooling demand.

When the VVT RTU or AHU provides heating and the VVT zone requires heating, the VVT zone damper modulates between an adjustable minimum and maximum damper position to satisfy the zone heating demand. When the VVT RTU or AHU unit mode of operation is the opposite of what is required in the VVT Zone, the VVT Zone damper overrides the minimum damper position and fully closes to prevent the zone from overcooling or overheating until the VVT RTU or AHU unit is no longer actively heating or cooling or has switched to the mode of operation required by the zone.

During unoccupied periods and subject to appropriate outside air lockouts, the associated VVT zones terminal load demand triggers the VVT RTU or AHU to start and operate in the heating or cooling mode until the heating or cooling demands have been satisfied for all the VVT zones.

Demand controlled ventilation

When a room is occupied, a local wall mounted CO2 sensor switches the damper minimum position set point from the minimum set point to the maximum set point when a rise of measured CO2 concentration above the adjustable CO2 set point occurs. The central VVT RTU or AHU monitors the associated VVT zones and increases the percentage of RTU supplied outside air in response to the VVT zones CO2 concentrations. The opposite occurs when the measured CO2 concentration decreases.

Wall sensor module

Use the wall module set point adjustment knob and the bypass push button on the wall temperature sensor module to adjust the local temperature slightly or to set the unoccupied mode. You can change the local heating and cooling set points with the local wall module set point adjustment and set the allowable offset.

Your adjustments do not affect the set points in use when the room is in the unoccupied or standby modes.