From building information models to simplified geometries for energy performance simulation

A major future challenge in the building industry is to reduce primary energy use of buildings. EU law now requires energy performance certificates to be issued for all buildings. Hence, energy performance simulation becomes an increasingly important topic. Accurate, yet efficient simulation depends on simple building models. Most of the required data can be found in Building Information Models (BIM), following the buildingSMART alliance's Industry Foundation Classes (IFC) schema. IFC has become an ISO standard and enjoys increasing support by CAD software. However, typical IFC models contain a lot of irrelevant data, in particular geometric representations, which are too detailed for energy performance simulation. Therefore, an algorithm is proposed for extracting input models for simulations directly from IFC models in a semi-automatic process, to overcome the current situation where simple models are manually built from scratch. The key aspect of the algorithm is geometry simplification subject to semantic and functional groups; more specifically, the 3D representations of walls, slabs, windows, doors, etc. are reduced to a collection of surfaces describing the building's thermal shell on one hand, and the material layers associated with it on the other hand. Test models from simple fictitious houses to complex models of real-world buildings have been provided to guide the development of the algorithm in an incremental manner. This paper presents the resulting algorithm and the current status of prototype software implementing it.