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AEC

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

8 Jun, 2006 By: AIA ,Rick Rundell

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BIM for building electrical design.

In the last few months, I've explored how the newly released Autodesk Revit Systems extends the Revit BIM (building information modeling) into mechanical, electrical and plumbing (MEP) engineering -- completing the building model by providing discipline-specific BIM solutions on the Revit platform across the entire building design enterprise.

Last month I reviewed how engineers can take advantage of BIM for building mechanical design. This month I do the same for building electrical design (figure 1).

Data-Centric Design
In last month's article I noted the importance of using a computable building model -- a dataset that a computer can operated on as a building. This type of building model captures the functional relationships between building elements and systems. Architectural, structural and MEP elements all know what they are, how to interact with each other and their roles within a larger system.

For the building mechanical design discipline, defining and understanding the physical relationships of building elements (the location, size and relationship between building components in 3D space) is as important as modeling and getting feedback on how the system functions (how much air flow should and can be delivered to a space and the pressure required to move that air through the ducts).

For the building electric design discipline, physical modeling takes a back seat to system modeling. Wires aren't actually routed in the model -- that's left to the contractor on site. The only things physically modeled are electrical devices and equipment such as lighting fixtures, transformers, generators, panel boxes, etc. However, system modeling is of the utmost importance (figure 2). Are there any devices not assigned to a circuit? What is the number and types of circuits? Is there adequate power and light for the space and its intended use?

These design considerations and calculations form the basis of an electrical engineer's challenge. The computable Revit Systems model is a perfect environment for this type of data-centric system modeling.

System Modeling
With Revit Systems, electrical engineers model the power and lighting circuitry of the building spaces. During system modeling, the user places light fixtures, power devices and equipment in the model and then creates a circuit connected to a distribution panel. The user defines wire types, voltage ranges, distribution systems and demand factors to ensure the compatibility of electrical connections in the design and prevent overloads and mismatched voltages (figure 3). To create a circuit: select an electrical device, click Create Circuit on the Options bar and then click Select Panel for Circuit and select a defined panel. To add additional devices to the circuit, click Edit Circuit on the Options bar, add additional devices using the available tools on the Design bar and then click Finish.

The resultant circuit model allows users to calculate the estimated demand loads on feeders and panels and to use these loads to adequately size equipment in the design environment. Load balancing is easy when managing circuits -- literally with the click of a button, users can balance electrical loads between the buses on their panels. These built-in circuiting tools also allow users to total loads and generate reports for accurate documentation.

To generate a panel schedule, from the View menu select New/Panel Schedule and then select a panel from the panel list. Panel schedules are available in the Project Browser under Reports (figure 4).

A system browser lets a user check the continuity of an electrical model to identify orphaned elements that are not connected to any system and makes sure that system elements are properly connected and contribute to system load requirements for optimized circuitry. After the circuits are defined, Revit Systems automatically wires the electrical devices by placing annotation that includes the homerun to the panel assigned to the circuit.

Built-in electrical calculations enhance the system design with engineering data, provide design decision support from the building model and reduce the burden of manual calculations and ultimately resulting in a coordinated electrical system design (figure 5). To place wire, select a device on the created circuit, press the Tab key to show the temporary wiring and click to select the highlighted circuit. On the Options bar, click Generate Arc Typing Wiring.

For example, Revit Systems can estimate lighting levels in rooms automatically based on the lights placed in the space, excluding daylight. The user just defines the reflectivity values of the room surfaces, attaches industry-standard IES data files to lighting, defines the calculation workplane height and the system automatically calculates the average estimated illumination value for the room (figure 6). Users can include calculated illumination in a report for design documentation.

Increased Coordination
Coordination between a building's electrical and mechanical systems is critical, as one powers the other. The data-centric approach of Revit Systems provides engineers with a holistic view of the building model and systems. For example, a user can review the electrical requirements on mechanical equipment and configure voltage and power load requirements to dynamically update in panel schedules.

In addition to building model and system coordination, a purpose-built BIM solution like Revit Systems automatically coordinates all design documentation as well. Like all Revit platform solutions, the drawings, sheets, views, schedules, reports and so forth are live views of the same underlying database. Therefore, electrical documentation such as electrical plans and panel schedules always are consistent.

Summary
Autodesk Revit Systems offers MEP engineers advanced features and functionality for building electrical and mechanical design. Data-centric system design helps engineers optimize system performance. Automated creation of engineering design data means users can make decisions faster and more accurately. Parametric change management helps eliminate coordination errors in documentation sets and minimizes coordination errors between engineering design teams -- as well as architects and structural engineers within Revit-based workflows.

The computable Revit building model allows firms to create, manage and share design information more effectively -- contributing to increased profitability, reduced risk and fewer inefficiencies in building design.