Application

Room Segment Functions
Device Control Functions HVAC
58
Siemens Industry, Inc.
Application Note
A6V11692042
Smart Infrastructure – Building Products
2019-04-01
Potential uses of the step-up include:
⚫ Keeping the flow setpoint high enough to support heat transfer from a coil
⚫ Keeping the flow setpoint high enough for effective sensing
Dual Duct Air Volume Flow Calculation
Air Volume Flow (VavSuAirFl1, VavSuAirFl2) and Relative Air Flow
(VavSuAirFlRel1, VavSuAirFlRel2) are calculated values computed from logic that
utilizes the following:
⚫ Separate Velocity pressure from the differential pressure sensor or other flow
sensing technology
⚫ Units conversion constant to convert to air velocity
⚫ Flow coefficient value for calibration at a specific airflow setpoint
⚫ Duct area in units compatible with the units conversion constant
⚫ Nominal airflow value (user entered)
⚫ Hood air volume flow value to aid in calculating the correct flow coefficient
value
First, air velocity is a calculated value computed from logic using the following
formula:
Where:
⚫ AirVEngrgUnits is the velocity of the air in engineering units that are compatible
with the other units used in the airflow formulas above
⚫ KEngrgUnits = constant for engineering unit correction [the “4005” (English
units) or “1.29” (SI units)
⚫ CSpanCal = constant to calibrate for sensor span (also called flow coefficient)
⚫ Pdifferential = differential pressure sensor reading from duct
Next, Air Volume Flow in flow units (VavSuAirFl) is calculated by the formula: