1. Mastering Autodesk Revit MEP 2016
CHAPTER 10: Mechanical Systems and Ductwork

2. Air Distribution Components
Air Terminals
Face-hosted for attachment to:
Ceilings, walls, or even duct
Level-hosted for areas without a ceiling
Can be copy/monitored from linked file
Copy/monitored objects represent only physical data, not design information
Air distribution components come in many different shapes and sizes. Depending on the design of the family, they can be mounted in a huge variety of ways. The designer must decide whether to have hosted fittings (and if so, which type of hosting) or to host to the level or workplane. There are different—and similar—ways of placing these objects, and some may be conflicting.

3. Equipment Components Air Conditioning/Handling Units
Can be represented “generically” with a box until specified
Typically non-hosted, placed at a level
Pad or rails can be modeled in the family itself, or family can be placed on pad/rails in project
Although basic in construction and with no manufacturer data attached, generic AC /AHU units can have the same number of parameters as a more detailed family. Dimensionally and performance-wise similar, the “concept” box can be swapped out during the detail design period for a more detailed manufacturer or “construction issue” family.
Placing of the majority of AC /AHU units is generally on the level that they are inserted on, with no offset. This can depend upon whether the unit is mounted on rails and whether those rails are part of the AC /AHU unit family or not.

4. Equipment Components VAV Boxes
Typically non-hosted families that are placed at a level and then given an offset to be located above the ceiling
Once an offset value is chosen, it will be used for subsequent placement
Connectors for duct, mechanical piping, and electrical
Generally created as non-hosted families, VAV boxes are usually mounted somewhere within the ceiling void, suspended from the underside of the slab above. In terms of placement, these are given an offset. The offset can be predefined, prior to the VAV being placed in the Properties palette.
Connections to both AC Units and VAV boxes can include heated and chilled water services and electrical for connecting to water and electrical systems.

5. Duct Components Duct Round, Rectangular, and Flat Oval shapes
Duct runs are not part of a system until connected to a terminal or equipment connector
Insulation can be applied (modeled) but will not be included in interference checking results
Ducts can be displayed in a variety of ways, including rectangular, round, or oval. Ductwork is a system family, the glue that holds systems together, but it also depends upon standard families to create a duct type.
Ductwork and its associated fittings are “systemless”—they do not form part of a system until connected to points on mechanical equipment or air terminals.
When running an interference check, know that duct insulation will not form part of the calculation.

6. Ductwork Duct Types Duct Systems
Shape and fittings defined per material
Duct Systems
Specify system classification and graphic overrides
Creating new duct ”types” is a way of managing the different materials and connections associated with a given set of ducts regardless of the airflow running through them. Fittings can be exchanged at any point through the design either individually or by selecting a given run of ducts and fittings.
It is easy to use view filters to distinguish between different system types for design visualization and documentation.

7. Ductwork Automatic Duct Routing Mechanical Settings Routing Solutions
Type and elevation for main runs and branches (per system)
Can be accessed during layout for custom instances
Routing Solutions
Network – Main run between components with branches off
Perimeter – Main run around perimeter of components with branches in
Intersection – combination of Network and Perimeter
When using the automatic routing tools, as a rule of thumb, work on small sections; all the feeds to a VAV box is one good example. This means the computer has fewer objects to calculate, and the routing suggestions have less room for error.
Once a system has been created, the Generate Layout tool is available on the Ribbon (when system is selected). The solutions are based on settings applied in Mechanical Settings for the project.
Use placeholder ducts for initial design. They are much easier to manipulate during design, and sizing and interference checks can be done.

8. Ductwork Manual Duct Routing Duct drawn at specified elevation
Justification settings – Top, Bottom, or Middle of duct
Duct can be drawn from connection points on equipment/terminals
Size acquired from connector data
Vertical runs can be drawn in section view or plan views (by changing offset during run)
Trim tool used for easy completion of runs
To begin manual duct routing, select the Duct tool from the Systems tab on the Ribbon, and then choose the type and its various options from the Properties box.
Note the default settings for Constraints, including Justification, Ref Level, and Level offset. The System type can be preselected but will change to match a connector in a different system.
Additional properties can be adjusted from the Options Bar and the Modify/Place Duct tab.
The duct can then be created/drawn to whatever path you choose. For vertical offsets, type the new height into the Offset box on the Options Bar, but for angled setup/down it is best to work in an elevation or sectional view.

9. Ductwork Duct Sizing System tools Duct run must be correctly connected
Systems can be checked prior to sizing
Methods
Friction, Velocity, Equal Friction, Static Regain
Combinations can be used
Constraints allow for limiting height or width
System tools
System Inspector
Use as a graphical inspection method
Show Disconnects
Displays open ends in systems
The most important factors to consider when using the duct sizing tools are that the ducts form part of a “system,” and this system should have a nominated name, not a default, which is created at the same time as the system being created. The system must also have a valid air flow, so either you specify the airflow of the Air Terminals or that flow is specified from the space and volume calculations.
Duct sizing will work correctly only where Air Terminals, Ducts, Duct Fittings, and Mechanical Equipment are seamlessly connected, with no gaps or open ends.

10. Ductwork Insulation and Lining Factors
Insulation and Lining are not taken into account during duct sizing or interference checking
Settings for Insulation and Lining are Instance parameters and must be applied to each duct and fitting
Manageable with schedules
When designing your system, you should be aware that Revit does not take into consideration external or internal insulation in sizing calculations or in clash detection. Duct insulation does not form part of any interference checking, so although you can see the clash, it does not get reported. In addition, duct lining can be shown on the plan but does not affect the Airway size. These factors may be important, especially in areas where accessibility is an issue and the designer should be extra vigilant in these situations.
Insulation or lining cannot be applied to placeholder ducts.