OpenBuildings™ Designer Help

Duct Sizer

Used to calculate duct sizes for transfer, supply, and return duct routes by computing duct sizes for centerline routing, resizing by optimizing route path duct sections. Used in 3D-routed duct system consisting of connected components to compute and list the Velocity Pressure exiting “change-in-flow” or “change-in-size” components in the interactive tables.

Accessed from:


  • Ribbon: Building Systems Design > Analysis > Mechanical > Duct Sizer


SettingDescription
Duct Design Data Defines the duct data settings used for sizing duct.
  • Material Type — Sets the material type for the duct.
  • Roughness — Sets the roughness of the duct material.

    The unit assigned is inch for Imperial and mm for Metric.

  • Flow Rate — Sets the value for rate of flow and unit of flow.
  • Flow Rate Units — The Imperial unit can be selected as ft3/min or fl3/sec, and the Metric unit m3/s, m3/hr or l/s respectively.
    Tip: You can set default flow rate units using the BMECH_FLOWRATE_UNIT configuration variable.
  • Velocity — Sets the velocity with which the flow travels in the ducts.

    The unit assigned per currently set under Unit System – ft/min for Imperial and m/s for Metric.

  • Pressure Drop — Sets the pressure drop value along the duct flow.

    The unit assigned per currently set under Unit System – H2O/100ft for Imperial and pa/m for Metric.

  • Air Temperature — Sets the temperature of air in flow system.

    The unit assigned is ºF for Imperial and ºC for Metric.

  • Atms Pressure — Sets the value for atmospheric pressure to effect compute realistic duct performance.

    The unit assigned per currently set under Unit System – psi for Imperial and mbar for Metric.

General
  • Unit System — Displays the units being used in duct sizing computing. When toggled applies one of the unit system.
    • Imperial — Displays and apply imperial measurement units.
    • Metric — Displays and apply metric measurement units.
  • Equivalent Diameter Equation — Defines a standard to compute the duct sizing equating the equation from two given standards.
    • CIBSE — When on, applies the CIBSE standards equation in computing the duct sizings.
    • ASHRAE — When on, applies the ASHRAE standards equation in computing the duct sizings.
Fixed Dimensions Sets fixed values that define dimension of the duct.
  • Use Fixed Value — When on, enables dimension fields for selected shape option. For rectangular ducts, the dimensions override the Rectangular Criteria set.

Note: The units in the bracket reflect the units assigned to the dimensions as per selected unit system; inch for Imperial and mm for Metric.

Rectangular/Oval Output Options Defines the duct data settings used for sizing rectangular duct.
  • Increment Step — Sets the step in which the next higher measurement is snapped.

    The unit assigned per currently set under Unit System – inch for Imperial and mm for Metric.

  • Max. Aspect Ratio — Sets the aspect ratio in terms of width versus depth (w/d) of the duct dimension.
  • No. Of Alternatives — Sets the number of permissible alternatives in the resulted list.
Shape Option
  • Shape — Defines one of the shapes to ducts, among three standard shapes.
    • Circular — When on, assigns round shape to duct being sized.
    • Rectangular — When on, assigns rectangular shape to duct being sized.
    • Oval — When on, assigns oval shape to duct being sized.
  • Dimensions — Sets fixed values that define dimension of the duct.
    • Fixed — Populates dimension fields for selected shape option.
      For Round ducts:
      • Diameter — Appears when Circular Shape option is selected. Sets diameter for the round duct.
      For Rectangular and Flat Oval ducts:
      • Width — Appears when Rectangular or Oval Shape option is selected. Sets width dimension for the rectangular / oval duct.
      • Depth — Appears when Rectangular or Oval Shape option is selected. Sets depth dimension for the rectangular / oval duct. The aspect ratio in the result is the width to depth ratio of a rectangular / oval duct.
    • Calculated — Assigns calculated duct dimension values. Effect upon Calculate.
Calculate Computes the duct size according to the parameters set.


The dialog divides Results in separate pane in the right. You can toggle the arrow to minimize the results pane to view or edit the Duct sizer settings.
Note: The currently set Unit System reflects the units displayed in results .
SettingDescription
Results Displays the calculated result of the duct sizing.
  • The result list — Displays the list of records of ducts sizing. Lists the following headings:
    • Shape – Displays the shape of the duct, as per shape selected in the Shape Option.
    • Dia. Eq. – Displays the diameter suitable for connecting inline equipments.
    • Size – Displays the size of the duct; the width and height dimensions for rectangular and oval ducts and diameter in case of round ducts.
    • Velocity – Displays the velocity of flow.
    • Pd – Displays the pressure difference of flow along the duct.
    • Vel. Pressure – Displays the velocity pressure of flow.
    • Pressure Coefficient – Displays the value of pressure coefficient.
    • Re – Displays the Reynolds number value that implies a number of different situations where a fluid is in relative motion to a surface.
    • Ratio – Displays the width to height size ration of the duct.
  • Density — Displays the density of the air flowing in the duct.
  • Dyn. Viscosity — Displays the dynamic viscosity of the air flowing in the duct.
  • Kin. Viscosity — Displays the kinetic viscosity of the air flowing in the duct. These are the resulted ideal values computed per set design conditions.
Place Duct Appears upon Calculate. Applies the current parameters to a selected duct.
Close Discards changes and dismisses the Duct Sizer.
Key-in: HVACUI LOAD DUCTSIZER
To Size Duct
Parent topic: Route Analysis