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Duct Centerlines

This section describes the commands used to draw duct centerlines.

Common Duct Information​

The values that can be specified for a duct are listed below.

  •  Starting Elevation: The starting elevation of the duct. The reference point for the starting elevation of the duct is set by the Vertical Alignment ▾. See the Elevation section for more information.

  •  Ending Elevation: The ending elevation of the duct. The reference point for the ending elevation of the duct is set by the Vertical Alignment ▾. See the Elevation section for more information.

  •  Vertical Alignment: ▾ Specifies the reference point used for the Starting Elevation and Ending Elevation.

    •  Center of Duct The elevations refer to the centerline of the duct. The duct will extend both above and below these elevations.
    •  Top of Duct The elevations refer to the top of the duct. The duct will extend below these elevations.
    •  Bottom of Duct The elevations refer to the bottom of the duct. The duct will extend above these elevations. If the duct has hangers, they will extend below this elevation.
    •  Bottom of Hanger The elevations refer to the bottom of the hanger for the duct. The hangers and the duct will extend above these elevations. If there is no hanger, the bottom of the duct will be at these elevations.

  •  Width: The width of the duct in inches. For round ducts, this value is used as the diameter. This value is the inside clear width of the duct. It does not include the width of the interior or exterior lining.

  •  Depth: The depth of the duct in inches. This field is disabled if the Shape ▾ field is set to Round. This value is the inside clear depth of the duct. It does not include the width of the interior or exterior lining.

  •  Shape: ▾ The shape of the duct. The fields that are available for specifying the size of the duct are based upon the selected shape.

    •  Round The duct will be round. The Width field is used as the diameter. The Depth field is disabled.
    •  Rectangular The duct will be rectangular.
    •  Flat Oval The duct will be ovoid.

  •  ☐ Lock There are ☐ Lock checkboxes next to the Width, Depth, and Shape ▾ fields. Check the box to lock the corresponding value. When the ducts are resized, locked values will not be changed.

  •  Maximum Depth: When the ducts are resized, the duct will change to the shape specified in the Shapes ▾ field if it exceeds this value.

  •  Airflow: ▾ The type of air flowing through the duct. The duct layers and pressure drop calculations are affected by this setting.

    •  Exhaust Exhaust ductwork. Vertical ducts are drawn with a full slash and a half slash.
    •  Outside Air Outside air ductwork. Vertical ducts are drawn with two half slashes.
    •  Return Return ductwork. Vertical ducts are drawn with a single full slash.
    •  Supply Supply ductwork. Vertical ducts are drawn with two full slashes.

  •  Graphics: ▾ How the ductwork is drawn in 2D.

    •  Automatic The ductwork is drawn double-line or single-line based upon the Width and the setting of the Maximum Single Line Width option. See the Ductwork options section for more information.
    •  Double The ductwork is drawn double-line.
    •  Single The ductwork is drawn single-line.
    •  Transparent The ductwork is not drawn. The air is carried through the duct to the next section. This setting is useful when you need to draw a custom fitting or piece of equipment in your duct system, or you need to connect ductwork across several floors on the same drawing. A transparent duct inserted through the custom graphic keeps the airflow connected and allows you to draw the graphics necessary for your design.

  •  Horizontal Alignment: ▾ Specifies the reference point for the duct construction line.

    •  Centered The construction line is the centerline of the duct. The duct extends to both sides of the construction line. Any transitions in the duct are concentric.
    •  Flat on Left The construction line is the left edge of the duct. The duct extends to the right of the construction line. Any transitions in the duct will be eccentric, with the flat edge on the left.
    •  Flat on Right The construction line is the right edge of the duct. The duct extends to the left of the construction line. Any transitions in the duct will be eccentric, with the flat edge on the right.

  •  ☐ Interior Lining Width: Whether the duct has interior lining. Check this box to specify the width of the lining. The ductwork size will include the interior lining when drawn in 2D and 3D.

  •  ☐ Exterior Lining Width: Whether the duct has exterior lining. Check this box to specify the width of the lining. The ductwork size will include the exterior lining when drawn in 3D.

  •  Material: ▾ The material used for the duct. The material is used to adjust pressure drop calculations and the appearance of the ductwork.

    •  Hard The duct is a hard duct. The specific type of material is not specified. The pressure drop calculations assume galvanized steel.

  •  Flex The duct is a flex duct.

  •  Layer System: ▾ See the Layer System section for more information.

  •  ☐ Same as Previous Whether the duct settings are based upon the previous duct. See the Previous and Next Ducts section for more information.

    This box is typically checked to reduce the number of times the ductwork in a run changes size. The sizing criteria for the ducts will often change the size at every takeoff. Check this box on select ducts to eliminate some of the transitions.

    The following values will be set to match the value of the previous duct:

    •  Vertical Alignment ▾
    •  Width
    •  Depth
    •  Shape ▾
    •  Airflow ▾
    •  Graphics ▾
    •  Horizontal Alignment ▾
    •  ☐ Interior Lining Width
    •  ☐ Exterior Lining Width
    •  Material ▾
    •  Layer System ▾

Sizing Criteria​

  •  Sizing Method: ▾ How the size of the duct is calculated. The fields that are available for specifying sizing criteria are based upon the selected method.

    •  Constant Velocity The duct is sized to maintain a constant velocity. A duct centerline set to use this sizing method has a circle with a V at the start of the duct.
      •  Maximum Velocity: The maximum velocity allowed in the ductwork. Ducts will be sized as small as possible without exceeding this value.
      •  Minimum Velocity: The minimum velocity allowed in the ductwork. The duct size will not change until the velocity drops below this value. If this value is set to 0, it will not be used during the calculation.
    •  Constant Pressure Drop The duct is sized to maintain a constant pressure drop. A duct centerline set to use this sizing method has a circle with a P at the start of the duct.
      •  Maximum Pressure Drop: The maximum pressure drop allowed in the ductwork. Ducts will be sized as small as possible without exceeding this value.
      •  Maximum Velocity: The maximum velocity allowed in the ductwork. The ductwork will be sized using the Maximum Pressure Drop value first. If the velocity exceeds the Maximum Velocity, the size will be increased. This setting is primarily used when sizing ducts with large airflow values. If this value is set to 0, it will not be used during the calculation.
    •  Static Regain The duct is sized using the static regain method. A duct centerline set to use this sizing method has a circle with an R at the start of the duct.
      •  Starting Velocity: The first duct in the run is sized using this value as the maximum velocity.
      •  Minimum Velocity: The minimum velocity allowed in the ductwork. If the Starting Velocity is not high enough, ducts at the end of the run can become very large. Setting this value limits how large the ducts can be.
    •  Same as Previous The duct is sized based upon the Sizing Method ▾ setting of the previous duct. A duct centerline set to use this sizing method does not have a circle at the start of the duct.

    Typically, you will set the Sizing Method ▾ for the first duct in a run and set all of the other ducts in the run to Same as Previous. If you need to change the Sizing Method ▾ in the middle of a duct run, do so at the single duct where the sizing method changes. Set all of the other ducts to Same as Previous. Setting the Sizing Method ▾ in a limited number of locations makes it easier to determine and modify how ducts are being sized.

  •  Shapes: ▾ The shapes used when sizing the duct. The first shape listed is used when the duct size is less than the Maximum Depth. The second shape listed is used when the duct size is greater than the Maximum Depth.

    •  Round to Rectangular The duct will first be sized round, then rectangular if the diameter exceeds the Maximum Depth.
    •  Round to Flat Oval The duct will first be sized round, then flat oval if the diameter exceeds the Maximum Depth.
    •  Square to Rectangular The duct will be rectangular throughout. Square ducts will be used if the size is less than the Maximum Depth.

Hangers​

  •  Hanger Type: ▾ The type of hanger. Controls whether hangers and their graphics are included.

    •  None No hangers are included. The other hanger fields will be disabled.
    •  Wrap The hanger will wrap around the item. A single support rod will be inserted in the middle of the item.
    •  Trapeze The hanger will be a support underneath the item with two support rods on either side.

  •  Size: The size of the hanger, in inches. The size is used to control most of the dimensions of the hanger graphic. The support rod diameter will be equal to this size. Other dimensions will be scaled based upon this size.

  •  Hanger Depth: The distance the hanger extends below the item, in inches.

  •  Starting Offset: The distance from the start of the centerline to the location of the first hanger, in inches.

  •  Ending Offset: The distance from the end of the centerline to the location of the last hanger, in inches.

  •  Spacing: The distance between each hanger, in inches.

  •  Left Width: The distance the hanger extends to the left side of the centerline, in inches.

    If this value is 0, the hanger will be wide enough to support the item. If it is greater than 0, the hanger will extend exactly that distance to the left of the centerline. It is possible this distance will be less than the width of the item the hanger is supporting. In that case, you need to increase the width. A width greater than necessary to support the specific item can be used to support a rack of items or to allow for future expansion.

  •  Right Width: The distance the hanger extends to the right side of the centerline, in inches.

    If this value is 0, the hanger will be wide enough to support the item. If it is greater than 0, the hanger will extend exactly that distance to the right of the centerline. It is possible this distance will be less than the width of the item the hanger is supporting. In that case, you need to increase the width. A width greater than necessary to support the specific item can be used to support a rack of items or to allow for future expansion.

  •  Ending Elevation: The elevation where the support rods end. The support rods will be drawn from the item up to this elevation. See the Elevation section for more information.