Revit MEP - Best practices

Objectives

1. To understand the best techniques to model MEP in Revit.

Prerequisites

1. The user is able to use Revit files.
2. The user has basic skills in BIM modelling with Revit MEP, and understands the terminology.

Description

MEP modelling in Revit can be very useful, but it’s key to manage our model properly, in order to keep it clean and organized, and the file fluent and weight optimized. This document explains key tips to achieve so.

Procedure

Project configuration

Setting to 0 the Mech Hidden value for Inside Gap and Outside Gap can provide substantial performance improvements, but we have to consider if it’s not necessary for documentation when working with hidden lines in a view.

Performance in views with the Hidden Line model graphics style enabled is directly related to the number of faces displayed in the view. Although elements are displayed as 2D lines in Revit views, in the model they are 3D objects made up of faces. The faces are processed by the Revit graphics system and display in the view as 2D lines.

Included in the Load Calculations panel of the dialog is a control that allows you to turn off load calculations for spaces. Unchecking the “Run calculations for loads in spaces” checkbox will keep Revit out from constantly updating these calculations, and show the loads as “Not Computed” in the Properties dialog. As soon as the box is rechecked, the values will be calculated again:

Temporary Dimensions

They play an important role in Revit Architecture, Structure and MEP. Sometimes in Revit MEP, temporary dimensions are too small to be legible. Users try to zoom in on them to read the information but they are still illegible, because they stay the same size no matter how far one zooms in. To fix this, click on the File→ Options→ Graphics. There you will find the dialog box to increase the “Temporary dimensions text appearance” size. Adjust this value to a usable size and you will be much more able to get your design information on the fly.

There is a calculations parameter in the System type properties. You can use it to limit or turn off system calculations. The Calculations parameter has three options:

• All
• Flow Only
• None

Depending on the option, the affected parameters may not be calculated, and their values are displayed as “Not Computed”. The affected parameters include flow, fixture units, velocity, velocity pressure, friction, friction factor, pressure drop, static pressure, and others.

MEP Specifications

MEP modelling

For your sheet views, use dependent views, which allow you to have multiple regions of an overall level in different views, without requiring to duplicate annotations.

Create logical systems for your connected networks, rather than leaving all elements on the default system. Associating elements into systems helps to streamline data propagation, and eases the analytical uses of systems, such as in pressure drop calculations.

Ensure that the Flow Direction parameter for connectors on families in the connected network is not set to Bidirectional, unless the family is placed in-line with connected networks like dampers and valves. The Bidirectional setting can make flow determination more difficult and thus impact regeneration performance.

We can make assemblies in order to get more handle in Cable trays and conduit modelling:

Use Worksets: electrical fixture, lighting fixture and all any unique systems, it is recommended that you create a workset for these specific systems to allow the access to multiple-user, and an easier control of the visibility.

When working with piping that has vertical components such as a riser, work in the 3D view to get a clear picture of how the routing works. Occasionally, fittings may not be placed in the correct direction. If this occurs, simply select the flip grip to change direction of the fitting.

Occasionally, when reducing a main duct or pipe down a size, it will appear as though the branches are no longer connected. If this happens, you can correct it by nudging the pipe from side to side (keyboard arrows). The connections will be re-established and appear correctly on the screen.

MEP families

We recommend the following:

Using Non-hosted Families

As it allows us to individualize our items and make them independent.

They are useful in areas that do not have a ceiling or for freestanding lights. They can be given an offset to the level at which they are inserted to show them above the floor.

The bad side is  that it’s necessary higher a level of coordination.

Not Using Specialty equipment Category

Specialty Equipment don’t belong to a MEP Family Category.

When a mechanical, plumbing or electrical discipline template is activated, the graphics displayed of this family will be totally different from the rest of the project.

Lookup tables

Lookup tables can be used to define parameter values in an external file. This is beneficial when you have multiple part sizes that are based on a table, but don’t want to create a separate family type for each size.

Revit provides a text_file_lookup function that can be used to read the necessary values from a comma separated values (.csv) file.

LOD

2D MEP Details

Use of Drafting tools to create riser-diagrams:

Taking for instance a power diagram, best practice is to have a library of commonly used symbols to facilitate quick and easy creation of your power diagrams, such as panels, transformers, generators, electrical fixtures, lighting fixtures.

The first step to produce your diagram is to create a detail section view of your switchboard equipment or main distribution panel.

Turn off all linked files and worksets and categories that do not need to be shown.

Use an elevation view as a base-plane of your equipment and the project levels.

Symbols can then be placed into this detail view to represent the electrical distributión equipment.

Detail lines can be drawn in the view to represent connections between elements (use line patterns to improve your draft).

Because of the disconnections between drafting view and modelled elements (the have not exactly the same ID), you have to coordinate data required in both places.

Visibility

Use coarse detail for architectural elements.

Avoid using the Fine detail level when working in mechanical views unless necessary, as multi-line representations slows down performance.

View by discipline: Mechanical, electrical and plumbing.

All categories belonging to Architectural or Structural Disciplines will appear half-toned.

Mechanical, Plumbing, and Electrical Categories will be shown according to Object Styles or Visibility/Graphics Overrides.

Mechanical, Plumbing, and Electrical Categories will not respect strictly what View Range determines, and will appear as long as they are included in the Primary Range (between Top and Bottom Plane).

When ducts and pipes overlap, the element below will appear in a Hidden Line style.

Create filters to display pipes coloured by the criteria that suits you. You can also add those filters to your template:

Tips & Tricks

• Keep the load calculations disabled until they are absolutely necessary.
• Create local systems for your connected networks, and keep to the minimum the bidirectional flow direction.
• Use non-hosted families and avoid the category of Specialty Equipment.
• Rely on lookup tables to define parameters on your elements.
• Use drafting views to create riser-diagrams.
• Take profit of the View by discipline option.

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Conclusion

Revit MEP offers interesting functionalities when it comes to representing, quantifying and planning building installations, but a good management of the model is key to keep our files light and organized. This document explains several aspects that help the modeller achieve such good management.