## 4 Results and Discussion
### A Case Study for the Environmental Performance Indicators in IFC  
The Horizon Europe-funded research project CHRONICLE (Grant Agreement number 101069722) aims to improve energy efficiency, occupant comfort, and building sustainability by leveraging IFC-based digital twins for renovation planning, carbon assessment, building operations, and long-term data management. The project runs for 42 months, from 1 July 2022 to 31 December 2025, with 18 partners and utilizing five pilot sites in five countries. Specifically, CHRONICLE designed an \"investment appraiser\" using IFC models to calculate embodied and operational carbon in various renovation scenarios. This tool provides an analysis of the life cycle cost (LCC) of the building based on several key performance indicators (KPIs), such as material quantities and other information extracted from the IFC model. It also integrates life cycle assessment indicators and dynamically calculates a carbon bill to facilitate stakeholders' decision making on climate-conscious renovations. The project has proposed a CEN/CENELEC Workshop Agreement (CWA) to develop a methodology for the calculation of the carbon bill of the refurbishment of buildings based on data from construction products provided in dEPDs [54]. The Workshop had its kick-off meeting on March 2025, and the draft generated was sent to a consultation period from June 26 th until August 21 st [55]. The goal is to publish the document before the end of 2025. The use of these tools to analyze the carbon footprint of the European built stock requires dEPDs to be structured in an efficient manner. This ensures that the content can be directly integrated into BIM models without human intervention or requiring very limited resources for the transfer. The BIM model can be used to create a digital twin of the building, enabling proactive interventions (e.g., refurbishment or maintenance) that reduce costs and downtime, improving the environmental performance of the building, as shown in [PERSON], [PERSON] et al. [56]. The development of integrated LCA methodologies during the research revealed certain limitations in data collection and processing workflows, and also in the environmental information included in the current IFC schema. The mapping of material and EPD data in IFC relies on material naming and labelling in the model, which is subject to human error due to differing labelling conventions, data entry errors, etc. The accuracy of the data mapping process is contingent on the accessibility of a comprehensive EPD database, as it necessitates a diverse and well-maintained dataset. In cases where the dataset is incomplete, lacking region- or manufacturer-specific data, the calculations may have a reduced accuracy, generating discrepancies during environmental impact assessments. This limitation can be addressed by directly providing relevant dEPDs to the assessment engine and by ensuring careful data mapping, a process which can be time-consuming. However, additional efforts have been made during the project activities to identify existing limitations and provide future recommendations for seamless integration of EPD data into the IFC structure. CHRONICLE developed several BIM models for project pilots. An IFC model from the project was used to test the transfer of LCA data from EN 15804 EPDs into BIM, identifyingthis information's EPIs (Environmental Performance Indicators). A building located in Zaragoza (Spain) was selected to analyze the applicability of identified gaps. The pilot is a former commercial building recently refurbished (2021) as social housing, improving the energy rating from level G to level C.  
The EPI representation format, standardized according to EN 15804 indicators, provides a tabular data structure that characterizes the EPI names, their units of measurement and declared values, arranged according to the LCA stages (modules A to D). However, the possibilities for standardizing the tabular data structures in IFC are limited based on the capabilities of the current official schema.