Evaluating the Impact of Reflecting the As-Is Building Condition in the BIM-Based Energy Modeling Process on Building Energy Simulations

Thermal conditioning of indoor air is basically related to heat transfer between inside and outside of buildings, which influences occupants' thermal comfort and the associated energy consumption for space conditioning. One significant parameter used in thermal analysis is the heat transfer coefficient of building envelopes. Considering deteriorated conditions of existing buildings' facades, modeling a building element with a constant surface-wide thermal property based on standard material databases is most likely to overestimate energy performance of existing buildings. This paper evaluates the impact of decreasing the gaps between the architectural information in the as-designed BIM and the as-is building conditions on the BIM-based energy modeling and analysis for existing buildings. By leveraging 3D thermal profiles reconstructed from 2D thermal images, the as-is thermal resistances are first characterized at point-level in 3D. Then, by mapping 3D point cloud data to the meshed BIM, the as-is thermal resistance values are automatically matched with the corresponding BIM element in gbXML schema. The updated BIM model is used as an input of energy simulation engines, and finally the Monte Carlo analysis based on the orthogonal sampling is conducted for impact analysis. Experimental results on several case studies validate the significant potential of reflecting the as-is building conditions from thermographic inspection in energy modeling, especially for buildings with wall degradations in the cold region. This provides building practitioners with the insight on how to improve the reliability of building energy analysis.