This AF uses a duct area calculation and input from a differential pressure sensor to calculate air volume flow.

Note: Unlike Supply air VAV 13, coefficient value is just a factor value without unit. Users need to fill in duct area during commissioning stage. The air volume flow value is calculated by coefficient value and duct area using a formula.

Following is an explanation to each option under Supply air VAV 12, press, duct area, ctr. as highlighted in the above screenshots:

Options

Details

Nominal air volume flow

Maximum air flow capacity of the VAV box.

Important! Must be no larger than 1.2 times the greater of the values of maximum air flow for ventilation or heating or cooling.

Supply air VAV duct area

Duct cross-sectional area, user-entered or calculated by automation station using the duct shape, dimension A and dimension B values. For user-entered method, VavSuDuctShape must be set to 4:Direct entry, otherwise data entry by user will trigger area calculation but the resulting value may be overwritten.

Supply air VAV duct shape

Duct cross-sectional shapes, as shown in the following list. Direct entry uses user-entered area, not controller calculation.

  • Rectangular
  • Round
  • Flat oval
  • Direct entry

Supply air VAV dimension A

  • Width for Rectangular duct
  • Diameter for Round duct
  • Total width (major dimension) for Flat oval duct
  • Not used for Direct entry

Supply air VAV dimension B

  • Height for Rectangular duct
  • Not used for Round duct
  • Height (major dimension) for Flat oval duct
  • Not used for Direct entry

Supply air VAV flow coefficient

The value used to calibrate span of air flow measurement; the value of calc flow coefficient is written to this object upon the Calibrate command.

Supply air VAV maximum air volume flow for cooling

Maximum air flow setpoint when in cooling mode; the air flow used for balancing when the Supply air VAV balancing mode = 1.

Supply air VAV minimum air volume flow for cooling

Minimum air flow setpoint when in cooling mode; the air flow used for balancing when the Supply air VAV balancing mode = 4.

Supply air VAV maximum air volume flow for heating

Maximum air flow setpoint when in heating mode; the air flow used for balancing when the Supply air VAV balancing mode = 2.

Supply air VAV minimum air volume flow for heating

Minimum air flow setpoint when in heating mode; the air flow used for balancing when the Supply air VAV balancing mode = 5.

Supply air VAV maximum air volume flow for ventilation

Maximum ventilation air flow setpoint for indoor air quality (IAQ) controller and for Rapid ventilation; the air flow used for balancing when the Supply air VAV balancing mode = 3.

Supply air VAV minimum air volume flow for ventilation

Minimum air flow setpoint for ventilation, whether fixed or controlled by indoor air quality (IAQ) controller; see more information about minimum ventilation flow in Ventilation control. The air flow used for balancing when the Supply air VAV balancing mode = 6.

Enable monitoring for missing air volume flow (optional)

  • 0:No: Set to No to remain with pressure independent control if very low / missing air flow is detected.
  • 1:Yes: Set to Yes to switch to pressure dependent control if very low / missing air flow is detected. With Yes or No, an invalid air flow signal causes pressure dependent control.

When the measured air volume flow falls below 5% of nominal, the air volume flow is very low / missing, the function “Enable monitoring for missing air volume flow” START working, the pressure control switch to dependent control.

When the measured air volume flow rises above 7% of nominal, air volume flow back to normal, the function “Enable monitoring for missing air volume flow” STOP working, the pressure control switch back to independent control.

Note: Default setting is Yes on Apptype version 1.001 to 4.001. and No on Apptype version 5.001.