BIM-based retrofit method (RBIM) for building envelope thermal performance optimization

•A novel BIM-based method to green retrofit existing building envelopes.•Integration of BIM, visual programming and multi-objective optimization algorithm.•Optimize building envelope overall thermal transfer value against retrofit cost.•Automated BIM data extraction and pushback using visual programming.•Validation using a case study of existing office building showed reliable results. Retrofitting building envelope thermal performance is crucial to ensure adequate interior thermal comfort of the building, minimize cooling load rate and, therefore, reduce overall building energy consumption. The retrofit process of an existing building envelope involves the design team selecting the best performing building materials and components based on various design variables and predefined design objectives. Worldwide, an overall thermal transfer value (OTTV) metric has been developed and used for assessing heat transfer through the building envelope. However, the application of OTTV implicates dealing with many design variables and much information, which makes the design decision-making process time-consuming and complicated. Furthermore, selecting the most appropriate design alternative in terms of OTTV performance while considering the most cost-effective design option could be a very challenging task. Therefore, this research proposes a method for retrofitting building information modelling (RBIM) to achieve a tradeoff design set between two conflicting objectives, namely minimizing OTTV and minimizing the retrofit cost. The prototype system derived from this method integrates BIM authoring tools (e.g., Autodesk Revit®), visual scripting (e.g., Dynamo), and a non-dominated sorting genetic algorithm (NSGA-II) customized in MATLAB®. The applicability of the proposed system is validated with a case study of an office building. The results show that the developed system provides a valuable design decision support system for retrofitting building envelope thermal performance while considering the retrofit cost. Additionally, the system shows an improved level of automation in terms of data management compared to the conventional methods.