Prior to exporting duct system data, each system must have at least one start point and one endpoint. A system is defined as any ductwork between a start point and one or more endpoints. A start point must consist of a fan or other air handling device. Endpoints must consist of outlet devices such as air terminals. Flow values must be assigned to outlet devices in order to properly size system components.
For example, a supply system uses an air handling unit to supply air to several rooms. Each room includes an air terminal as the outlet for the air. In this example, the system includes all ductwork from the air handling unit to each air terminal. If there was no air handling unit in the drawing, you would not be able to export the system data.
You should also consider these factors prior to exporting data:
- Start points can be fans, air handling units, or similar MvParts such as a VAV boxes, mixers, or economizers.
- To ensure proper sizing, assign flow values to all outlet devices, such as air terminals. For more information on modifying MvPart properties to assign flow values, see Configuring Mechanical Parts for Analysis.
- If the outlet device is an end cap, it is assigned a flow value of zero.
- Variable air volume controllers (VAV boxes) with 2 connectors, such as single duct or shut off VAV boxes, are considered part of the duct run unless they are ending a branch. If they end a branch, they must have a flow value assigned. If they do not end a branch, the flow value assigned to them is not used.
- VAV boxes with more than 2 connectors, such as dual duct boxes, are considered end points. Any ductwork beyond the VAV box is not considered. The flow value assigned to the VAV box connector is used for analysis.
- Duct segments that contain takeoffs are considered as one plenum duct when exported. If you want the analysis tool to assign different sizes to different parts of the duct, use the break command to divide the duct into multiple segments, and insert transition fittings where appropriate.
Prior to exporting, you should also consult your external analysis package for any additional requirements you must include in your system. For example, you may need to specify the ASHRAE fitting type for all duct fittings as shown in Specifying ASHRAE Fitting Types. There may also be system design constraints that you need to consider.
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