HVAC Duct Sizer PlusOnline Help

The HVAC Duct Sizer Plus (Android Edition) application allows you to quickly size one HVAC duct run. You can select from two modes of sizing:

1. Size by Airflow: This mode of sizing is appropriate for new duct systems. You can specify the airflow, aspect ratio (for rectangular or oval shaped duct) and the unit friction loss or velocity to calculate duct dimensions, air velocity, nominal dimensions, and more.
2. Size by Dimensions: This mode of sizing is appropriate for existing duct systems. You can specify the duct height, width (or diameter), airflow or velocity to calculate the remaining properties including airflow, velocity, unit friction loss, and nominal dimensions.

You can also specify a number of additional properties of the duct and air including temperature, air pressure and duct material type.

Details

When you first open the HVAC Duct Sizer Plus application, you can select from one of two modes of duct sizing. Select either one to begin sizing the ductwork:

Size by Airflow: This mode of sizing is appropriate for new duct systems. You can input the total airflow (CFM or L/s), unit friction loss (inwg/100ft or Pa/30m) or air velocity (fpm or m/s), and aspect ratio. The following is an explanation of each of the inputs:

1. Airflow (CFM or L/s) Textbox: You can input the airflow value in CFM (L/s) directly into this textbox. When you tap within this textbox, a keyboard will pop up allowing you to type in a value. Press the 'Next' button on the keyboard to move to the next input and register the value. You can also press the 'Back' button to hide the keyboard (Please note that this keyboard appears when you tap within any of the textbox controls.). The results will automatically update based upon your newly inputted airflow value. You can input a maximum value according to the max airflow value in the preferences form (see below).
2. Airflow Slider: This slider control allows you to easily change the airflow by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form. As you slide the indicator along this control, the results will immediately update. Also, the value represented by the position of the indicator on the slider control will appear in the airflow textbox discussed above.
3. Friction/Velocity Button: This button allows you to toggle between inputting a unit friction loss value (in wg/100 ft or Pa/30 M) or an air velocity value (fpm or m/s). Depending upon the option that you choose will determine the type of value that you can input in the accompanying textbox and slider control.
4. Friction/Velocity Textbox: This textbox allows you to input a unit friction loss or air velocity value, depending upon the option you selected above. The results will automatically update based upon your newly inputted value. You can input a maximum value according to the max friction or velocity value in the preferences form.
5. Friction/Velocity Slider: This slider control allows you to easily change the unit friction or velocity value by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form. As you slide the indicator along the control, the results will immediately update. Also, the value represented by the position of the indicator on the slider control will appear in the friction/velocity textbox discussed above.
6. Aspect Ratio Textbox (only for rectangular and oval shaped duct): This input allows you to specify the ratio of the duct width to duct height (for rectangular and oval shaped duct only). The closer the aspect ratio is to 1, the more "square" it will be. If you want to size ductwork where the duct height is greater than the duct width, then input a value less than 1. If you want to size ductwork where the duct width is greater than the duct height, then input a value greater than 1. The duct dimension results will automatically update based upon your newly inputted aspect ratio value. You can input a maximum value according to the max friction value in the preferences form.
7. Aspect Ratio Slider: This slider control allows you to easily change the aspect ratio by using your finger to slide the indicator to the left or right. As you slide the indicator along this control, the duct dimension results will immediately update. Also, the value represented by the position of the indicator on the slider control will appear in the aspect ratio textbox discussed above. As you move the slider indicator, it will increase or decrease by a specific "step" value. For example, if this step value is 1, then the aspect ratio will increase or decrease by 1 as you move the indicator along the slider control.

Size by Dimensions: This mode of sizing is appropriate for existing duct systems. You can input the duct height, width, or diameter and the total airflow (CFM or L/s) or air velocity (fpm or m/s). The following is an explanation of each of the inputs:

1. Duct Height (in or cm) Textbox: This option appears for rectangular or oval duct. You can input the height of the existing duct. You can input a maximum value according to the max dimension value in the preferences form (see below).
2. Duct Height Slider: This slider control allows you to easily change the duct height by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form. As you slide the indicator along this control, the results will immediately update. Also, the value represented by the position of the indicator on the slider control will appear in the airflow textbox discussed above.
3. Duct Width (in or cm) Textbox: This option appears for rectangular or oval duct. You can input the width of the existing duct. You can input a maximum value according to the max dimension value in the preferences form (see below).
4. Duct Width Slider: This slider control allows you to easily change the duct width by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form.
5. Duct Diameter (in or cm) Textbox: This option appears for round duct, only. You can input the diameter of the existing duct. You can input a maximum value according to the max dimension value in the preferences form (see below).
6. Duct Diameter Slider: This slider control allows you to easily change the duct diameter by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form.
7. Airflow/Velocity Button: This button allows you to toggle between inputting an airflow value (CFM or L/s) or an air velocity value (fpm or m/s). Depending upon the option that you choose will determine the type of value that you can input in the accompanying textbox and slider control.
8. Airflow/Velocity Textbox: This textbox allows you to input an airflow or air velocity value, depending upon the option you selected above. The results will automatically update based upon your newly inputted value. You can input a maximum value according to the max airflow or velocity values in the preferences form.
9. Airflow/Velocity Slider: This slider control allows you to easily change the airflow or velocity value by using your finger to slide the indicator to the left or right. The values will increase or decrease by a "step" value that can be specified in the preferences form. As you slide the indicator along the control, the results will immediately update. Also, the value represented by the position of the indicator on the slider control will appear in the airflow/velocity textbox discussed above.

Explanation of Calculated Results

The calculated results are immediately updated as you change values in any of the controls discussed above. This section talks about the calculated results for both of the input modes discussed above.

Two columns of results are displayed. The column labeled "Exact" is exactly that: results that are precisely calculated without any rounding involved. Since most duct runs are prefabricated to nominal dimensions, the "Rounded" column of data is displayed. This column contains dimensions that are rounded to the nearest even or odd dimension. The resulting friction loss and velocity values are also updated. Depending upon whether you are sizing rectangular, round, or oval duct, the types of results displayed will vary. The following is an explanation of all of the result values with an indication of the duct shape represented:

1. Airflow (CFM or L/s): This result is the calculated airflow. It appears in the "Size by Dimensions" mode.
2. Duct Dims (in x in or cm x cm): The duct dimensions appear (repeated) in the "Size by Dimensions" mode.
3. Equivalent Diameter (in or cm): This result appears in both input modes. It displays the calculated equivalent diameter (if it is rectangular or oval shaped duct). This means that a round duct of this diameter exhibits the same pressure loss characteristics as the rectangular or oval duct.
4. Duct Height (in or cm): This result appears in the "Size by Airflow" mode. It displays the calculated duct height (if it is rectangular or oval shaped duct).
5. Duct Width (in or cm): This result appears in the "Size by Airflow" mode. It displays the calculated duct width (if it is rectangular or oval shaped duct).
6. Duct Diameter (in or cm): This result appears in the "Size by Airflow" mode. It displays the calculated duct diameter (if it is round duct).
7. Friction (in wg/100ft or Pa/30m): This result appears in both input modes. It displays the selected (or calculated) duct friction loss.
8. Velocity (fpm or m/s): This result appears in both input modes. It displays the calculated air velocity.

Duct Settings

This form can be accessed by pressing the 'Menu' button on your Android-based phone. Two tabs will appear: 'Preferences' and 'Help'. Select the 'Preferences' tab to display a list of duct-related preferences:

1. Units: This dropdown control allows you to specify whether to display all values in English (Imperial - IP) or Metric (SI) units.
2. Outputted Duct Dimensions: This dropdown control allows you to specify the rounding properties of the outputted duct dimensions. You can select either even or odd rounded dimensions. For example, if the calculated dimensions for a specified airflow/velocity are 41.5 x 40.3 and the specified rounded dimensions are "even", then the calculated rounded dimensions will be 42 x 42. The friction loss and velocity results under the "Rounded" column will update according to the rounded dimensions.
3. Duct Shape: This dropdown control allows you to specify the shape of the duct run. You can select either rectangular, round, or oval shaped duct. When you return to the main duct input form, the controls, labels, and results will immediately update to reflect the new duct shape.
4. Duct Material: This dropdown control allows you to specify the type of duct material. Each duct material type represents a duct roughness value. The following is a list of the available duct material types:
   
   1. Aluminum
   2. Fibrous glass duct liner
   3. Flexible duct, metallic
   4. Galvanized steel
   5. PVC plastic pipe
   6. Smooth liner
   7. Spiral steel
   8. Uncoated carbon steel
   
   After selecting a duct material type, the duct roughness value will update in the text box below the control.
5. Duct Roughness (ft or m): This input allows you to specify the duct roughness value in feet or meters. This value is automatically updated according to the duct material you selected above. You can also override this value.
6. Temperature (F or C): This input allows you to specify the average temperature of the air traveling through the duct work. If the duct work is part of a cooling system, then the average temperature will be around 55 to 65 degrees F (13 to 18 degrees C).
7. Air Pressure (psia or kPa): This input allows you to specify the average outside air pressure in pounds/square inch absolute (psia) or kiloPascals. Standard pressure at 0 feet elevation is around 14.7 psia (101.4 kPa).
8. Max Airflow (CFM or L/s): This input allows you to specify the maximum allowable airflow. After returning to the main input form, the slider control will update according to the new value. You will not be allowed to specify a value greater than the maximum airflow.
9. Airflow Step Value: This input allows you to specify the increment value as you move the indicator along the airflow slider control on the main input form.
10. Max Friction (in wg/100 ft or Pa/30 m): This input allows you to specify the maximum allowable friction loss per 100 feet or per 30 m. After returning to the main input form, the slider control will update according to the new value. You will not be allowed to specify a value greater than the maximum friction loss.
11. Friction Step Value: This input allows you to specify the increment value as you move the indicator along the friction slider control on the main input form.
12. Max Aspect Ratio: This input allows you to specify the maximum allowable aspect ratio. After returning to the main input form, the slider control will update according to the new value. You will not be allowed to specify a value greater than the maximum aspect ratio.
13. Aspect Ratio Step Value: This input allows you to specify the increment value as you move the indicator along the aspect ratio slider control on the main input form. For example, if you specify a value of 0.5, then the as you move the indicator on the aspect ratio slider control, the values will increase or decrease by 0.5 (i.e. - 0.5, 1.0, 1.5, etc.). This value must be at most 1/2 of the maximum aspect ratio value inputted above.
14. Max Velocity: This input allows you to specify the maximum allowable velocity. After returning to the main input form, the slider control will update according to the new value. You will not be allowed to specify a value greater than the maximum velocity.
15. Velocity Step Value: This input allows you to specify the increment value as you move the indicator along the velocity slider control on the main input form. For example, if you specify a value of 10, then the as you move the indicator on the velocity slider control, the values will increase or decrease by 10 (i.e. - 100, 110, 120, etc.).
16. Max Duct Dimension: This input allows you to specify the maximum allowable duct dimension (height, width, or diameter). After returning to the main input form, the slider control will update according to the new value. You will not be allowed to specify a value greater than the maximum duct dimension.
17. Dimension Step Value: This input allows you to specify the increment value as you move the indicator along the dimension slider control on the main input form. For example, if you specify a value of 2, then the as you move the indicator on the dimension slider control, the values will increase or decrease by 2 (i.e. - 6,8, 10, etc.).

To return to the main input form, click the 'Back' button.

Explanation of the Duct Sizer Formulas

The formulas used to calculate the duct size results are based upon equations from the ASHRAE 2017 Handbook of Fundamentals. The duct sizing calculations are based upon the iterative Darcy and Colebrook equations. The duct sizing method is constant friction.