Autodesk Research

Green Building XML (gbXML)
June 26, 2009

gbXML Source

With recent emphasis on energy efficiency in buildings, energy and environmental analysis are becoming increasingly important aspects of design consideration. Within this context, gbXML is becoming a defacto industry standard for defining thermal models, with support from various industry standard CAD tools. Once the model has been prepared in a CAD tool, i.e. Revit, then gbXML can be used to export an analytical model to analysis software. For example, this analytical model can be used either in conjunction with Autodesk Green Building Studio to evaluate the energy profiles and carbon footprints of design early in the design cycle or it can be imported to Autodesk Ecotect to perform a full range of environmental analysis and simulation. Green Building Studio is for whole building energy analysis, forecasting how a building will consume resources and providing estimates in tabular report form. Ecotect tools measure how the environment may impact the building performance over time and provides graphical displays of information that allows architects and designers to interact with the data in real time. The following chart provides a high-level summary of each product's analysis capabilities:

  Autodesk Green Building Studio
Measures how the building consumes resources
Autodesk Ecotect
Measures how the environment impacts building performance
Life cycle costs +  
CO2 Emissions +  
LEED Credit Analysis (Lighting) +  
Water use +  
Energy use and cost +  
Airflow/Ventilation + +
Thermal Loads + +
(Day) Lighting
(LEED & Energy Savings)
Luminosity Fluxes
+ +
Shading   +
Solar   +
Acoustic   +
Climate + +
Energy code compliance   +

Green Building Extensible Markup Language (gbXML) is a schema that was originally developed by GeoPraxis for use in Green Building Studio, an online energy analysis advising tool. This schema is geared towards converting a CAD model into input for the DOE-2 energy analysis tool and EnergyPlus.

gbXML consists of a very specific set of definitions and data requirements focusing only on energy analysis. Its geometric requirements deal only with spatial volumes and thermal zones with relatively simple polygonal boundary surfaces. Therefore, any CAD tool that supports gbXML must export its complex model information in a simplified form.

Prior to exporting the model into gbXML format, we need to define zones within our model to create a series of distinct homogenous volumes of air. Using software such as Revit Architecture or Revit MEP, a designer can add room objects, spaces and HVAC zone objects which will be imported into Ecotect or Green Building Studio through the gbXML format for further analysis.

Simple Revit File

This simple Revit example consists of some very basic elements such a window, skylight, door, floor, roof and four walls (above, left). Using Revit Architecture we define a room object (above, right) and then we will export this model into gbXML format in order to create an analytical model.

Exporting gbXML from Revit

In this view, we are looking at a room object as it appears in the gbXML export window within Revit Architecture (above, left). We can also view the analytical surfaces and their hierarchy prior to exporting into gbXML (above, right). A list of elements are presented in as a tree structure on the right side of the window.

Importing gbXML into Ecotect

We can import the gbXML file into Autodesk Ecotect for further analysis. The above image shows the import window displaying the content summary of the gbXML file.

Analysis in Ecotect

In Ecotect we can perform analysis ranging from solar studies to acoustics analysis, thermal analysis, ventilation and air flow. The following image shows a simple configuration of a shadow study based on the time of the day and location on Earth.

Green Building Studio Result

We can also import the same gbXML model into Autodesk Green Building Studio. Using Green Building Studio we can run whole building analysis and assess energy goal viability of an intended design. The image above displays an early analysis of our simple example outlining the estimated energy and cost summary. Furthermore, Green Building Studio also provides guidance on the LEED daylighting 8.1 credit and LEED water efficiency credits 1, 2 and 3.

Green Building XML (gbXML) Sample Files
ZIP - 6.428MB

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