In Practice: linking Revit to IES
Posted : March 24, 2010 by Craig Wheatley, Category: Building Regulations
One of the key challenges facing today’s building designers is understanding and tackling how to incorporate sustainable design principles into existing workflows and processes.
A ‘good design is sustainable design’ ethos promoted by quantitative analysis can make a great impact. Architects get quick environmental feedback on design iterations and environmental engineers can input more into the design. Achieving this kind of effective collaboration and cross-discipline understanding, in my opinion is core to achieving truly sustainable, energy-efficient building design.
The advent of BIM (Building Information Modeling), and better integration between analysis and design tools, is helping push this more integrated, information sharing approach to design team working. In particular, the Green Building XML schema, referred to as “gbXML”, was developed to facilitate information transfer from building information models to design/energy performance analysis tools.
We’ve working hard at IES to drive such integration by developing plug-ins that link our tiered suite of analysis tools to Revit Architecture, Revit MEP and Google SketchUp so users can build their designs in Revit or SketchUp and then easily translate and analyze them in an iterative fashion. gbXML was used to streamline the data flow from Revit to the IES <Virtual Environment> in the IES VE Revit Plug-in.
The IES Revit plug-in is already helping companies undertake customized environmental performance analysis for fast, easy-to-implement, sustainable engineering and design. KlingStubbins chose IES’ analysis tools to ensure proper coordination throughout the entire design process, from early stage design to more advanced thermal, and daylight analysis. The company undertook a three month study – combining engineers and architects from three of their six offices. It delved into the IES Revit plug-in export capabilities and the analysis applications of the IES VE.
“In a three month period, we were able to get examples of a number of easily achievable studies that could be done on real projects, in real time, and can help us quickly get answers to questions on our sustainable projects,” commented Jonathan Weiss, Director of Sustainability at KlingStubbins. “Optimizing orientation, making effective sunshades, testing different envelope configurations, each of these are things we need to do, and often we need to nail down long before detailed energy models are completed. The VE gives us good data as well as a clear way to graph and illustrate the results for our internal team, as well as for our clients.”
Since this study, we’ve made several enhancements to the IES Revit plug-in, which were designed to improve real-world model transfer. It can now handle more challenging and complex geometry, as well as allow users to choose the level of geometry detail exported. The VE sets no explicit limits on the number of surfaces that it can import, and so with these plug-in enhancements it is now possible to import intricate geometry, such as highly detailed curtain walling systems, multi-faceted shading surfaces and mullions, and additional complex shapes and junctions. This can greatly enhance design workflow and simulation accuracy.
However, in certain situations importing the maximum level of detail can be overkill and increase simulation run times. For example, if mullions are not being used for solar shading. This is why adding the element of user choice is an important new capacity. The new version of the IES plug-in allows users to determine the level of detail with which the model is translated from Revit. The “Export Complexity” options range from the basic, to how shading surfaces are handled, to whether curtain wall mullions are counted as shading surfaces:
- Simple: Curtain Walls and Curtain Systems are exported with one “huge” opening with the total opening area equal to all openings; a curtain wall with 50 panels is exported as 1 opening.
- Simple with Shading Surfaces: Export with simple type and shading surfaces.
- Complex: Curtain Walls and Curtain Systems are exported with several openings, panel by panel; a curtain wall with 50 panels is exported as 50 openings.
- Complex with Shading Surfaces: Include complex type and shading surfaces.
- Complex with Mullions and Shading Surfaces: Include complex type, shading surfaces and mullion. Mullions in Curtain Walls and Systems are exported as shading surfaces. A “simplified” analytical shading surface is produced from a mullion based on its centerline, thickness and offset.
So just what is the IES <Virtual Environment> (aka VE)? It’s a collection of building performance modeling and analysis modules leveraging a single integrated data model. The intent is to provide the high quality information required to design, build and operate better performing, more sustainable buildings without having to build a different model for each type of analysis.
The IES tools and reports available vary in level of detail and analysis type offered, based on the tier of the VE software that is engaged. This allows us to provide tools that can be applied by all from the earliest stages of the design process right through to completion and even into operation. Analysis options include annual energy/carbon consumption, building loads, daylighting and electric lighting, climate, water, airflow, LEED credits and a range of strategies such as natural ventilation, mixed mode ventilation and night-time flushing.
Burt Hill, having implemented Autodesk’s Revit Architecture in 2003, found the move to using IES’s software for building performance analysis fit perfectly into the holistic view of building information modeling that they wanted to shape their process around.
“One of the key advantages of the Revit/IES integration is that it accommodates a fully integrated design approach and facilitates interdisciplinary decision-making,” commented Dustin Eplee, 
leader of Burt Hill’s Energy Analysis team, which was formed as an in-house consulting group dedicated to building simulation. “Architects and MEP engineers can use the analysis tools for their own baseline calculations and MEP design; then our team tackles the more in-depth building simulation, analysis and certification tools available in the IES VE resulting in a comprehensive, integrated analysis of building performance.”
“When the architectural design model is also the energy model, energy modeling and responsiveness become core components of the design process. For example rooms are designed explicitly as 3D energy-consuming volumes instead of just floor space bounded by walls.”
A recent Burt Hill project, the Springfield Literacy Center in Pennsylvania, presented an opportunity to use IES VE software from the early concept stage of the design process, alongside Revit. A full case study looking at how orientation, building envelope, thermal properties, shading devices, daylight levels, energy use and LEED compliance were considered as the design progressed can be read here.
In addition, IES Software, with its direct plug-ins to Autodesk Revit and Google SketchUp, were chosen by Canadian mechanical and electrical consulting engineering firm MCW Consultants for the design of major LEED projects, as part of the company’s overall shift toward BIM. The company is currently using the software on the following projects:
However, it is important to note that gbXML is not perfect and limitations transferring information between BIM and energy simulation software still exist. A key issue to understand, when looking to cycle through design options in a timely manner, is that there are some fundamental differences between an energy model for analysis and an architectural model used to generate construction documents. For example, many BIM elements do not support information exchange identifying the thermal performance characteristics that are needed to run energy analysis. Therefore, the user is required to specify these values at the point of translation, so the analysis can be performed with the appropriate characteristics.
In addition, when undertaking analysis at different stages of the design process, you want to bring the appropriate level of detail to the analysis; so that you don’t get bogged down in the inputs, when the results are the important piece that should be considered in-depth.
At early stages, if you take the perspective of the energy modeler they want to include the minimum amount of information to answer the question at hand, to reduce the variables and the analysis time. If you take the perspective of the architect, the visual character of the overall model is important to convey the design intent, as well as the details to express the layering of the idea(s).
We’ve found that Architects tend to want to analyze their ‘specific wall design with specific layers’, when in fact at an early stage identifying the wall as an R-24 (thermal value) may provide enough information to develop comparative analysis between cases.
In order to take advantage of the IES ability to integrate BIM and Building Performance Analysis, the Revit model needs to be developed with this workflow considered. You may have heard the term ‘garbage in, garbage out’, and like any type of analysis, the usefulness and accuracy of the results depend greatly on the quality of the inputs.
Since it is not a direct conversion from Revit to IES, there are many areas users need to note while modeling in Revit to successfully translate into a design/building performance model. We have developed a white paper which provides guidance on best modeling practices that allow analysis cycles to inform the design; testing ideas as the building evolves. Online training also provides ‘live examples’ of these best practices and others.
Properly utilizing integrated building performance analysis can be a powerful tool to evaluate and inform design decisions. However, the most impact is made when modeling is incorporated holistically right from the earliest stages, well before key design decisions are set in stone. The aim is to reduce overall energy consumption, while looking at applying low carbon technologies and renewable energy sources. This performance-led lean, clean, green approach should also include consideration of occupant comfort.
In short, in order to design a high-performance building and implement an integrated process, the traditional design process needs to change. No longer can the design team leave analysis too late in design development. By working holistically from concept stage, the project team will find a number of the high-impact strategies on the table and should be able to achieve 50% efficiencies and beyond. If they wait till later, there may still be ‘system efficiencies’ on the table, but it will be a reduced set, and may be more costly.
As Steven Chu, the US energy secretary, points out – greater efficiency, particularly in buildings, will significantly reduce the number of power plants built. If that’s not incentive to start exploring Integrated Building Performance Analysis and BIM, then I don’t know what is!!
Refer to www.gbxml.org for more detailed information regarding gbXML documentation.
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