This function computes the flow and velocity based on the measured pressure and the K factor. K-Factor is often used in terminal unit controls to calculate actual airflow. From iteration to iteration, the Function Block keeps track of the last state of the auto set offset. On power up/reset this is set to "true" so that auto offset cannot be executed on a reset or power up.
Figure 1: FlowVelocity Formula
Figure 2: FlowVelocity Function Block |
Figure 3: FlowVelocity Property Sheet |
Inputs
Input Name |
Description |
Engg Unit (Metric/Imperial) |
Offset (In & Par) |
Input pressure offset correction to adjust the Flow to Zero. Numeric: 32-Bit Floating Point value >=-inf-<inf. |
Pa OR inW |
Pressure (In & Par) |
Air pressure which is measured via a pitot tube. Numeric: 32-Bit Floating Point value >=-inf-<inf, Default: Null. |
Pa OR inW (inches water gauge) |
AutoSetOffSet (In & Par) |
Input correction pressure offset Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
Pa OR inW |
ClearOffSet (In & Par) |
Reset correction pressure offset to value 0. Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
Pa OR inW |
Area (In & Par) |
Area (ft^2) Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
(m2/hr) )/ft^2 |
KFactor (In & Par) |
Actual flow corresponding to a velocity pressure sensor output of 1" w.g. or 249Pa. Please describe what it is, where it comes from. Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
(m3/hr) )/ft^3/min (CFM) |
Table 1: Inputs of FlowVelocity Function
Output
Output Name |
Description |
Engg Unit (Metric/Imperial) |
Flow |
Airflow in CFM/(ft3/min) Numeric: 32-Bit Floating point value, >=-inf- |
(m3/hr) )/ft^3/min (CFM) |
Velocity |
Air flow velocity (ft/min). Numeric: 32-Bit Floating point value, >=-inf- |
m/hr OR ft/min |
Table 2: Output of FlowVelocity Function
Parameters
Parameter Name |
Description |
Engg Unit (Metric/Imperial) |
Flow Par |
Airflow Numeric: 32-Bit Floating point value, >=-inf- |
(m3/hr) )/ft^3/min (CFM) |
Offset Par |
Input press Offset correction (Pa/inW). Stored Flow offset value for display. Numeric: 32-Bit Floating Point value >=-inf-<inf. |
Pa OR inW |
Velocity Par |
Air flow Velocity (m/hr/ft/min). Numeric: 32-Bit Floating point value, >=-inf-<inf. |
m/hr OR ft/min |
Pressure Par |
Air Pressure Pa OR inW Numeric: 32-Bit Floating Point value >=-inf-<inf, Default: Null. |
Pa OR inW |
AutoSetOffSet Par |
Input correction pressure offset (Pa OR inW) Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
Pa OR inW |
ClearOffSet Par |
Reset correction pressure (Pa OR inW)offset to value 0. Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
Pa OR inW |
Area Par |
Area Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
(m2/hr) )/ft^2 |
KFactor Par |
Actual flow in corresponding to a velocity pressure sensor output of 240Pa/ 1" w.g. Numeric: 32-Bit Floating value: >=-inf-<inf, Default: Null. |
(m3/hr) )/ft^3/min or CFM |
Table 3: Parameters of FlowVelocity Function
Examples
If Pressure is 2.02 in/wc, offset is 0.02 in/wc, KFactor is 1015 cfm, and the area is 0.54 square feet (10-inch diameter), the flow will be 1015 ft/min, and velocity will be 1879 ft/min.
Figure 3: Example FlowVelocity Function Block
Refer to General Description for general information about IRM N4 Function Blocks.