Ductwork Calculations

The Ductwork Calculations command is used to calculate the airflow in ducts, size the ducts, and calculate the pressure loss in ducts.

To calculate these values in ducts, go to

DM HVAC->Calculations->Ductwork Calculations

Duct Calculations Dialog Box

Calculations--Duct Calculations dialog box

Ducts to Use: Controls the ducts that are used in the selected calculation.

All Ducts: Performs calculations to all the ducts in the project, not just those on this drawing. This selection takes the most time.
Ducts in a Branch: Performs the designated calculation on the duct that is selected out to the diffusers. It does not apply the calculation to the ducts leading to the fan.
Ducts in a System: Performs the calculation on all the ducts connected to the selected duct, both those towards the diffusers and those towards the source.

Calculate CFM: Press this button to calculate the airflow in the selected ducts.The total airflow in CFM in all ducts will be updated and stored in the database. You can query the duct to view the airflow in each section. Nothing else is changed or calculated.

Calculate CFM and Size Ducts: Press this button to calculated the airflow in the selected ducts and size them based upon the newly calculated airflow. The total airflow in CFM in all ducts will be updated and stored in the database. You can query the duct to view the airflow in each section. The duct size and shape will be updated both in the database and on the drawing.

Calculate CFM, Size Ducts, and Calculate Pressure: Press this button to calculated the airflow in the selected ducts, and size them based upon the newly calculated airflow, and calculate the pressure in the ducts. The total airflow in CFM in all ducts will be updated and stored in the database. The duct size and shape will be updated both in the database and on the drawing. The pressure drop in each section, and the total pressure drop in the duct system will be calculated. You can query the duct to view the airflow and the pressure drop in each section.

Calculating Values

After you press one of the three Calculate buttons, the dialog box will close. You will be prompted based upon the Ducts to Use selection you chose.

All Ducts

The selected calculations will immediately start on all the ducts in the project.

Ducts in a Branch

You will be prompted to select the duct at the start of the run to perform the calculations in.

Select duct or label at the start of the branch:

After you select a duct, the calculation will be performed on the selected duct and all the ducts between it and the diffusers.

Ducts in a System

You will be prompted to select a duct in the system to perform the calculations in.

Select duct or label in the system:

After you select a duct, the calculation will be performed on all the ducts connected to the one you selected.


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