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AEC

1-2-3 REVIT: BIM for MEP Engineering, Part 2

8 May, 2006 By: AIA ,Rick Rundell

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The impact of BIM on building mechanical design.

Last month, I began a three-part series of articles about how the newly released Revit Systems BIM (building information modeling) software for MEP (mechanical, electrical and plumbing) engineering improves the MEP design and documentation process. This month, I drill down into mechanical design, examining how that building discipline can take advantage of BIM. Next month, I'll do the same for electrical design.

Holistic Model-Based Approach to Design
BIM relies on a computable building model -- that is, a model in software operated on by a computer as a building; a model that captures the functional relationships between building elements and systems.

Using a conventional CAD system for design, MEP engineers and designers visualize the 3D design in their brain and transfer it to a 2D drafted representation. Some CAD systems designed specifically for MEP system design allow designers to model the system geometry in 3D for the purposes of coordination and extracting drawings, but because the drawings are extracted from the model, change management between the drawings and the model as the design evolves involves a manual process.

In contrast, the Revit Systems BIM, a purpose-built parametric building modeler, is an integrated digital environment for design and engineering, analysis and documentation. MEP engineers work directly in the model, and the drawings themselves are part of the BIM. Intuitive layout tools make system layout fast and easy. Engineers modify their design by dragging design elements to move or change them on the screen. All model views and drawing sheets update automatically whenever a change is made anywhere for accurate and coordinated designs and documents at all times.

Data-Centric Design
This data-rich, computable Revit Systems model is used to drive the design process with a host of tools to aid in the layout of mechanical ductwork and piping as well as plumbing systems.

Revit Systems enables users to perform many engineering calculations directly in the model, such as sizing mains, branches or whole systems at a time, using industry-standard methods and specifications (such as the ASHRAE fitting loss database). System sizing tools are integrated with the layout tools and instantly update the size and design parameters of duct and pipe elements without file exchanges or third-party applications.

To size an air supply system, select a duct run and click Sizing on the Options bar. Specify the method of sizing to use in the Sizing dialog box and click OK (figure 1).

Revit Systems automatically provides duct and pipe routing solutions between any two points. The routing path is constrained by the engineer, who selects fitting or connection preferences to meet specific design criteria. The software then finds and displays multiple routing path, allowing the engineer to choose the option that works best for a design. To view routing solutions, select a duct system component -- such as an air terminal -- that is assigned to a system. Press the Tab key to see the temporary duct routing graphics (figure 2) and click to select the highlighted system. On the Options Bar, click the Convert button and then click the arrow buttons as needed to view the different solutions for routing the ductwork. Click Finish when a solution is found (figure 3).

During the layout of the plumbing design, a user just defines the rise over run, and the software automatically calculates invert elevations according to industry codes and tags them at the ends of pipe runs, which minimizes the guesswork and manual calculation on sloped pipe. The software also automatically places all plumbing risers and drops to reduce the tedious aspects of system modeling.

Design Insight
The Revit Systems BIM also is used to give the MEP engineer feedback as the design progresses.

You can color-code ducting or piping by a design parameter (such as low or high pressure, fluid service, velocity range, flow rate, etc). This visual representation of design data gives engineers instant insight into the design intent for a particular system.

The System Inspector tool displays the critical flow path for a duct run and provides a quick method for viewing the design specifications for each duct segment in a system. This feedback allows an engineer to quickly identify areas of the system where they could modify the design for maximum performance and efficiency.

To inspect an air supply system, select the duct run and click System Inspector on the Options bar. Click Inspect on the Design bar, and as you move your cursor around in any view, the design specifications for each system component are shown (figure 4). Click Finish on the Design Bar when done.

Revit Systems detects clashes between any MEP system components (and when used in a Revit-based design team, between architectural and structural elements from Revit Building and Revit Structure as well). Detection of interferences during the design process reduces costly field rework.

The computable model created by Revit Systems contains the necessary level of detail to enable direct engineering analysis. To facilitate that analysis, Revit Systems supports export to gbXML for third-party analysis applications such as Trane's TRACE 700 and eliminates the time-consuming task of transferring data manually back and forth between modeling and analysis packages.

Increased Coordination
Many mistakes and delays in building construction are caused by poorly coordinated design documents. In the Fifth Annual FMI/CMAA Survey of Owners -- a 2004 survey conducted by FMI Corporation and the CMAA (Construction Management Association of America) -- 70% of owners said they are seeing a decline in the quality of design documentation. For firms with slim profit margins, any rework costs exacerbate the bottom line, and MEP profit margins are notoriously slim (from 5% to 15% depending on the type of project).

A purpose-built BIM solution such as Revit Systems automatically coordinates all design documentation because views, drawings, schedules, reports and so forth are all live views of the same underlying database. The result is a dramatic reduction in documentation errors, producing an accurate design that requires less rework.

BIM solutions also allow the design and documentation of MEP systems to occur concurrently instead of serially, because project deliverables are created dynamically while the design work is done. The production of design documentation requires less time and effort by the design team, increasing project throughput. In addition, a concurrent design and documentation effort tends to naturally increase project coordination, with team members working in real time on the execution of the design, minimizing the amount of information loss between participants.

Enhanced Communication
Last month I explained how coordination and communication between MEP team members is streamlined through the use of Revit Worksharing. Revit Systems also includes several other key features that enhance project communication between team members, architects, clients and contractors.

During the design process, you can use color-filled room plans to visually communicate design intent. You can customize the color-coded rooms based on critical design parameters such as room types or airflow requirements. These color-filled plans are just another live view of the BIM, and they update automatically whenever design changes are made.

To create a color-fill plan of space design criteria, select Color Fill on the Drafting Design bar. Click Edit on the Options bar and define a color-fill scheme as desired. Select the Color Fill type from the list on the Options bar and place the legend in a plan view (figure 5).

Revit Systems can export to, import from or link with a variety of CAD formats, including DWG, DWF, DXF and DGN. This compatibility assures data exchange with software applications as well as clients, architects and partners. For example, you can use 3D DWG files output from Revit Systems in Autodesk VIZ or Autodesk 3ds Max software to create photorealistic renderings of a building's MEP engineering designs for enhanced communication with clients or team members. Similarly, you can use DWF output from Revit Systems in Autodesk Design Review software to facilitate the review process.

To render a view, click Model Graphics Style on the View Control bar and select Rendered with or without Edges (figure 6).

Revit Systems can also read and write ACIS solids, which gives users a way to import and export Revit Systems models to and from AutoCAD or Autodesk Architectural Desktop. You can use this method to cut sections and perform visual interference detection.

Users can easily upload files from Revit Systems to an Autodesk Buzzsaw site for Web-based collaborative project management. Added functionality even allows for automatic conversion of Revit Systems files to either DWG or DWF format.

Summary
Autodesk Revit Systems offers MEP engineers features and functionality for building mechanical design. The Revit building model delivers information that is coordinated, internally consistent and computable, allowing you to provide clients a clear overall vision of their projects. Better coordination and faster design helps raise the quality and increase the profitability of MEP projects.