Duct Centerlines

This section describes how 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 location of 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 location of the ending elevation of the duct is set by the Vertical Alignment. See the Elevation section for more information.

Vertical Alignment: What location on the duct the starting and ending elevations refer to.

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 (in): 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 (in): 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 shape that is chosen.

Round: The duct will be round. The Width field is used as the diameter. The Depth field is disabled and ignored.
Rectangular: The duct will be rectangular.
Flat Oval: The duct will flat oval.

Lock: There are three Lock checkboxes, next to the Width, Depth, and Shape fields. Checking the box will lock the corresponding value. When the ducts are resized, the locked value will not be changed. Any values that are not locked will still be changed.

Sizing Method: How the size of the duct is calculated.

The first duct in a run should have a sizing method set. All of the other ducts should be set to Same as Previous.

If you need to change the sizing method in the middle of a duct run, you should set this value at the single duct where the sizing method changes. All of the other ducts should be set to Same as Previous.

Setting the Sizing Method in a limited number of locations makes it easy to determine how your ducts are being sized and makes it easy to change it when necessary.

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. If this value is set to 0, it is not used during the calculation. If is set to a number, the duct size will not change until the velocity drops below this value.

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. If this value is set to 0, it is not used during the calculation. If it is set to a number, the ductwork will be first sized using the Maximum Pressure Drop value. If the velocity exceeds the Maximum Velocity, the size will be increased. This setting comes into play when sizing ducts with large airflow values.

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 that will be allowed in the ductwork. If the starting velocity is not high enough, the ducts at the ends of runs can become very large. Setting this value sets a limit on how large they are allowed to be.

Same as Previous: The duct is sized based upon the Sizing Method setting of the previous duct. Most ducts should use this setting. A duct centerline set to use this sizing method does not have a circle at the start of the duct.

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 all be rectangular. Square ducts will be used if the size is less than the maximum depth.

Airflow: The type of air flowing through the duct. The duct layers are chosen based upon the airflow. Pressure drop calculations are based upon the airflow direction.

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 Options->Ductwork section for more information on this option.
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. A transparent duct inserted through the custom graphic keeps the airflow connected and allows you to draw whatever graphics are necessary for your design.

Horizontal Alignment: The horizontal alignment specifies what the duct construction line refers to.

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 or not the duct has interior lining. If this box is checked, you can specify the width of the interior lining. The ductwork size will include the interior lining when drawn in 2D and 3D.

Exterior Lining Width: Whether or not the duct has exterior lining. If this box is checked, you can specify the width of the exterior lining. The ductwork size will include the exterior lining when drawn in 3D. The exterior lining is not drawn in 2D.

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

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 or not the duct settings are based upon the previous duct.

This box is most often 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. You can select ducts and check this box to eliminate some of the transitions.

The previous duct is the duct that is in the direction of the fan or air handler from the current duct. If the Return and Exhaust Arrow Direction option is set to Toward Diffusers, the previous duct is the one that points to the current duct. See the Options->Ductwork section for more information on this option.

prev_duct_pic

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

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

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 the size. Other dimensions will be scaled based upon the 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 hangers between the first and last hanger, in inches.

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

If the 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 it is support. 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 the 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 it is support. 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 on specifying this elevation.


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