The VAV airflow controller adjusts airflow to accomplish cooling and ventilation, and to support heating from the heating coil.
Each function has an operating range selected by the engineer to satisfy particular physical objectives. This design separates minimum cooling flow and minimum heating flow from the flow rate needed for ventilation.
The ventilation rate can be constant, vary with room occupancy mode, or vary according to IAQ measurements. These factors have no affect on the flow rate needed for the heating and cooling processes and devices (airflow through heating coil, airflow needed for ceiling louver, etc.).
The following table provides suggestions for setting parameters affecting airflow when the control system is in the cooling, ventilation and heating part of the control sequence. See Operating Diagrams in Section 1 for a pictorial of the relationship of these parameters.
Object | Description | Most common use |
|---|---|---|
VavSuAirFlMaxC | Supply air VAV maximum air volume flow for cooling | The highest flow rate for the terminal or space that corresponds to cooling load. |
VavSuAirFlMinC | Supply air VAV minimum air volume flow for cooling | The lowest flow rate for the terminal or space that allows cooling to work properly. |
VavSuAirFlMaxH | Supply air VAV maximum air volume flow for heating | The highest flow rate for the terminal or space and should be half of the cooling max to comply with standard codes. |
VavSuAirFlMinH | Supply air VAV minimum air volume flow for heating | The lowest flow rate for the terminal or space that allows heating to work properly. |
VavSuAflMaxVnt | Supply air VAV maximum air volume flow for ventilation | The highest flow rate that the DCV loop can request (can be equal to max cooling). |
VavSuAflMinVnt | Supply air VAV minimum air volume flow for ventilation | The lowest flow rate for ventilation to work properly. |
AirFlMinRCmf | Minimum room air volume flow for comfort | The primary airflow rate (not OA ventilation) required when the space is occupied. |
AirFlMinRPcf | Minimum room air volume flow for pre-comfort | The primary airflow rate required when the space is in standby mode. |
AirFlMinREco | Minimum room air volume flow for economy | The primary airflow rate required when the space is unoccupied. In many spaces this should be |