Building Energy Modeling (BEM)
Stub: This article needs expansion.
Introduction
There is currently 2 BIM format related to energy modeling : gbXML and IFC (using IfcRelSpaceBoundary2ndLevel) Most energy analysis software reads gbXML. Some read IFC. Generating geometry for gbXML and IfcRelSpaceBoundary is quite similar. Information contained in both format is different. There are significant challenges (in 2022) with IFC and space boundaries, BuildingSMART International is working to improve the situation by improving the Information Delivery Manual (IDM) for Building Energy Modelling (BEM). The current status (in 2022) can be seen in a video from bS Virtual Summit Spring 2021 in the presentation BR5 - Jeffrey Ouellette - Building Energy Modelling (BEM).
See the Building Energy Modeling (BEM) category for more general info and tools!
Note to editors: Add a gbXML vs IFC features comparison
Energy modeling workflow (/!\Work in progress/!)
Modeling the building
Building need to be modeled with all data relevant to energy analysis :
- Building geometry : Walls, Slabs, Doors, Windows, Spaces etc…
- Energy data : Thermal transmittance, wall layers, thermal conductivity, solar transmittance, light transmittance etc… Overmodelled building often lead to error and/or uselessly complex computation. A energy model should be simple and contain only energy relevant information.
Bonsai
Bonsai allows you to create, modify an IFC targeting energy analysis. You can either:
- Rework an IFC coming from another authoring tool. This is probably the most efficient workflow currently. It allows you to enhance your model and fixes common known issues incoming from popular authoring software.
- Create a model from scratch. You might want to take a look at topologic and related projects for more automation.
Energy specific geometry
An algorithm need to generate energy specific space boundaries
Export to common energy exchange formats
Software need provide an Ifc or gbXML.
Revit
Configuration
TODO
Known issues
Warning: lastly tested with Revit 2021. revit-ifc 21.2.1 IFC 2x3 and 4 :
- export boundaries at middle of the wall instead of interior face.
- roof boundaries are oversplitted if they host an element (eg. skylight / hole for lift top)
- type B boundaries are not exported IFC4 :
- CorrespondingBoundary attribute is not filled
- ParentBoundary attribute is not filled
ArchiCAD
Configuration
By default ArchiCAD use IFC4 reference view MVD which do not contain IfcMaterialLayerSet(Usage). So layered wall will not contain thickness of each layer. Use a custom IFC translator using parametric
Known issues
Warning: lastly tested with ArchiCAD 24 IFC 2x3 and 4 :
- window and door boundaries are not coplanar with their host
- There is no hole for window and door boundaries in their host
- type B boundaries are not exported IFC4 :
- CorrespondingBoundary attribute is not filled
- ParentBoundary attribute is not filled
Adaptation to local standards
Both IFC and gbXML are not directly usable for local standards as each country have it’s own specification. [Add an exemple]
A tool for adjusting an .ifc file to local regulations is BIMxBEM which currently has a configuration to support Swiss standards for energy modeling. Contact the developer and you can start making a new localization.
Scientific article or conference paper on energy modeling
| Full text
available ? | publication
See also
- There is a discussion tag on our forum for Building Energy Modeling (BEM)