Modeling Mechanical Systems

BIM for Architecture, Engineering, and Construction Curriculum

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  • Unit 4 | Multidisciplinary Collaboration
  • Lesson 5: Modeling Mechanical Systems


In this lesson, students will learn how to model mechanical systems that provide ventilation and conditioned air to the spaces inside a building. These systems are typically referred to as heating, ventilation, and air-conditioning (HVAC) systems. 

Students will place components to model the essential elements of an HVAC system—air handling units and diffusers—and link these elements using ductwork to create systems that supply to the spaces and return air to the handlers. 

The endpoint of the lesson will be a mechanical model that can be used for mechanical system analysis and detailed mechanical design, as well as shared with the other members of the design team and disciplines affected by the mechanical design decisions.

Copying Shared Elements into a Mechanical Model

Link the preliminary architectural model to an Autodesk® Revit® MEP host project and use the Copy/Monitor tool to copy shared levels and grids as the starting point for the mechanical design tasks.

You will place components to model the HVAC equipment and devices later in this lesson, so you do not need to copy any fixtures from the linked model.

Modeling Exposed HVAC Systems

Model exposed HVAC systems (where the ductwork is visible and not concealed by a ceiling) using tools in the HVAC Panel of the Home tab. You can create two types of systems:

  • Supply systems that move conditioned air from air handling units to supply diffusers
  • Return systems that move air from return diffusers back to the air handling units

The essential steps include:

  • Place air handling unit components. 
  • Place supply diffusers and return diffuser components at locations for these terminals.
  • Connect the diffusers to the air handling units with ducts. 

To effectively move fresh air to where it is most needed, supply diffusers are typically placed along the perimeter of a space near doors and windows (and away from the return air intake). Return air diffusers are strategically placed to draw the conditioned air through the space.

You can place ducts individually, or use Revit software’s auto-routing tools to generate recommended ducts layouts based on the equipment connections, duct sizes, and connectors required.

Modeling Closed Plenum HVAC Systems

You can also model closed plenum HVAC systems (where the enclosed ceiling space is used as a return air plenum) using tools in the HVAC Panel of the Home tab. In these systems:

  • Supply air is moved to the supply diffusers through ducts that are typically concealed in the ceiling space.
  • Return air is moved from return diffusers mounted on the ceiling through the return air plenum.

The guidelines for locating diffusers in exposed HVAC systems also apply here. Place diffusers strategically to draw conditioned air through the space.

As with exposed systems, you can place ducts individually, or use Revit software’s auto-routing tools to generate recommended layouts. Since the ductwork is typically concealed by a ceiling, you can use rectangular ducts, which are typically less expensive than exposed round ducts.

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