There are two control strategies for VAV applications:
- Serial fan operation: The air volume is only increased if the valve's or reheater's positioning signal is fully open and the room temperature exceeds or breaches an additional offset.
- Parallel fan operation: The fan speed is increased in parallel to the valve's or reheater's positioning signal.
The two strategies are illustrated in the following example using a heating and cooling valve.
Serial
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Y | Output signal |
| TR | Room temperature |
SpH | Effective heating setpoint |
| SpC | Effective cooling setpoint |
YH | Heating valve |
| YC | Cooling valve |
VavSuAirFlMaxH | Supply air VAV maximum air volume flow for heating |
| VavSuAirFlMaxC | Supply air VAV maximum air volume flow for cooling |
VavSuAirFlMinH | Supply air VAV minimum air volume flow for heating |
| VavSuAirFlMinC | Supply air VAV minimum air volume flow for cooling |
OfsVavSttH | Offset for VAV start for heating |
| OfsVavSttC | Offset for VAV start for cooling |
| VAV volume flow |
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Figure: Example of a serial control strategy using modulating VAV
Parallel
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Y | Output signal |
| TR | Room temperature |
SpH | Effective heating setpoint |
| SpC | Effective cooling setpoint |
YH | Heating valve |
| YC | Cooling valve |
VavEndSpdPrlH | VAV end speed by parallel operation for heating |
| VavEndSpdPrlC | VAV end speed for parallel operation for cooling |
VavSuAirFlMinH | Supply air VAV minimum air volume flow for heating |
| VavSuAirFlMinC | Supply air VAV minimum air volume flow for cooling |
CoilVlVSttPrlH | Coil valve start position by parallel operation for heating |
| CoilVlVSttPrlC | Coil valve start position for parallel operation for cooling |
| VAV volume flow |
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Figure: Example of a parallel control strategy using modulating VAV
The control strategy can be configured in the application using the following parameters for heating sequence.
Description | Name | Default value |
|---|---|---|
Operating variables volume flow system for cooling 0:Serial | VavOp | 1:Parallel |
Operating variables volume flow system for heating 0:Serial | VavOp | 1:Parallel |