Keyword

1 Introduction

The energy refurbishment of existing buildings is seen as one of the most important strategies for reducing greenhouse gas emissions in the building sector. To address the challenges of climate change and post-pandemic recovery, the European Commission (2020) launched a new strategy as part of the European Green Deal to give a boost to the renovation of the building stock called “A Renovation Wave for Europe”. Its declared objective is to at least double the annual energy renovation rate of residential and non-residential buildings by 2030 and to foster deep energy renovations. In this framework, the technological innovation brought by building information modelling (BIM) in the construction sector can play a very important role, thanks to the advantages in all stages of the process, from the early phases of the acquisition of geometric and energy-related building data to those involving the management and monitoring of operating building performance. For example, BIM allows for the creation of accurate models of buildings at current state that constitute digital, easily searchable and updatable databases of all sorts of information about a building and, at the same time, that can be imported in software for specialized analyses such as the energy performance study. This is possible thanks to interoperability: in fact, in an open-BIM workflow, all participants from different disciplines can collaborate and exchange project information by using open, non-proprietary formats.

However, several barriers still hinder the full use of BIMs for energy analyses, such as issues in only partial interoperability among software and lack of technical knowledge of professionals. As stressed by Heffernan et al. (2017), interoperability issues typically result in architects communicating the design of a building in one model and an energy consultant reproducing that design within a new building energy model (BEM). Sanhudo et al. (2018) provided a comprehensive review of building information modelling for energy retrofitting, from the acquisition of geometric and energy-related data concerning a building to the use of as-is models for energy analysis, including interoperability issues with BIM authoring tools. Andriamamonjy et al. (2019) provide an in-depth overview of three main strategies to improve interoperability between BIM and building energy performance simulation tools. The most flexible is the strategy based on the identification of exchange requirements, aiming to make the BIM model the container of all information required for the various uses, including building energy analysis. It does not rely on proprietary tools or formats, but aims to make the BIM models exported to IFC compatible with the information exchange requirements for energy analysis. The above-cited publications show the great attention towards the use of BIM for the study of building energy performance and the need to overcome interoperability problems.

In Italy, since the entry into force of the so-called BIM Decree (MIT 2017), introducing gradually increasing obligations for the adoption of BIM-based methodologies for buildings and infrastructures, the number of buildings for the construction and renovation of which the use of BIM is required is slowly but steadily growing. Many administrations are beginning to equip themselves with the necessary tools for this purpose, also with the aim of considerably speeding up the internal procedures for checking and approving project proposals. In this framework, the work of guideline and process documentation drafting in the perspective of open BIM, carried out by the national State Property Agency (Agenzia del Demanio, ADM), represents an interesting reference in the Italian context (ADM 2021). Moreover, ADM’s work proves that it is becoming common in public tenders to commission BIM “as-is” models together with energy audits. It is a practice to be encouraged in order to discern the current state of the existing building stock and promote its renovation, but professionals struggle with the difficulty of including energy audits into the BIM process. Indeed, out of the software tools that the Italian Thermo-technical Committee (CTI) certifies for building energy performance calculation, according to relevant technical regulations, only a few have started a process of more or less deep introduction into the BIM process.

In the framework of the research where this work is included, Centi et al. (2019) provided an in-depth study of these software tools and their capabilities, according to some predefined BIM- and energy-related criteria (e.g. IFC import, IFC export, building modelling, buildingSmart certification, etc.).

Starting from the application on case studies, the research that is briefly introduced in this paper has focused on the identification of the existing interoperability issues between BIM authoring and Italian certified energy analysis software tools and on some proposals for their optimization. Such issues regard the incomplete and/or incorrect import of IFC models exported from BIM authoring software into building energy modelling (BEM) and analysis tools. On the other hand, these also affect the export to IFC of the details and the results of the energy analyses, which can be part of thorough reports, drafted by the energy modeller and linked to the IFC model in the Common Data Environment, but are not included in the IFC model exported from the BEM software. In other words, the BEM software is only used to run the simulations on the model, but its results as of now are not implemented in the IFC model of the building.

Having said that, this paper introduces some recommendations—targeted at the professionals in the sector—for the definition of as-is IFC models of buildings with the aim to make the importation in energy analysis software as seamless as possible, regardless of the software tool used. Additionally, in order to populate those models with the main results of the energy analysis, a series of parameters to be included, firstly in the form of custom property sets, were individuated. The objective of these actions is to support and, at the same time, valorize the work of the professionals carrying out energy audits, while highlighting the potential of BIM for greater knowledge and digitization of the building stock.

The Italian Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) has worked in closed cooperation with several stakeholders for the drafting of the Guidelines for Energy Audits of Buildings, published as a national standard/technical specification in 2020 (UNI/TR 11,775). The final scope of this study is to integrate the process of energy audit, described step-by-step in the Guidelines, within a BIM perspective to support professionals and facilitate the adoption of BIM in the process of refurbishment of existing buildings.

2 Methodology

Two phases characterize the methodology of the research discussed in this paper:

Phase 1: “from BIM to energy analysis”, aimed at:

  • The identification of interoperability issues between software tools for BIM authoring and energy performance analysis;

  • The drafting of recommendations for the creation of building information models optimized for energy analyses.

Phase 2: “from energy analysis to BIM”, aimed at:

  • The valorization of the work of the energy auditors and BIM-related potential

  • For greater knowledge and digitization of the existing building stock;

  • The identification of energy parameters (Pset) to be included in the model of a building to populate it with the results of the energy performance analysis.

2.1 From BIM to Energy Analysis: Interoperability Issues and Possible Solutions

Figure 6.1 illustrates the process of the first phase of the research, based on actual case studies (i.e. buildings subject to energy audit).

Fig. 6.1
A flow chart has levels B I M authoring software, a viewer, and software. Level 1 has parametric modeling and I F C model export. Level 2 has I F C model analysis and verification. Level 3 has energy analysis, energy model completion, I F C model import, and verification.

Process from BIM to energy analysis

Full size image

The process, which has required in the beginning many iterations and optimizations, consisted of three main phases, involving three different software categories, i.e. for BIM authoring, BIM viewing, and building energy modelling (BEM).

First, a parametric model of the case study building was developed by means of a proprietary BIM authoring software and exported into an IFC2 × 3 file. Then, the exported IFC file was analysed and checked in terms of geometry and content by means of a BIM viewer, before being imported into the BEM software. The model could then be completed of the information needed for the energy analyses in the selected BEM software. It is possible to point out several issues that limit the process of IFC import into the BEM tool. Information relating to the geometry and envelope components of the building is in general imported correctly, but in an incomplete way. Next, it is necessary to check and complete the geometry of the imported model as well as to characterize the spaces, thermal zones, and technical systems, in order to carry out the energy performance simulations.

Starting from the application of the above-described process of specific case studies, recommendations for modelling were developed aimed at maximum interoperability between BIM authoring and BEM software, highlighting limits and problems and proposing general solutions. The scope is to make the process in Fig. 6.1 as seamless as possible, contributing to the elimination of the iterations represented by the “return arrows” (i.e. changes to the model and its export settings) through the suggestion of specific actions for the BIM modeller to perform. The recommendations detail aspects that range from the nomenclature of elements to their geometric and stratigraphic characterization inside the BIM authoring software and they concern the correct definition (also from an energy point of view), the optimization and the check of model geometry, building elements, materials and layers as well as (thermal) spaces and zones. The work has also attempted to clearly identify the additional operations needed for the control and completion of the imported model, in order to manage the expectation of what can be done with the used BEM software. In general, it is suggested to refer to the guidelines of the individual software houses for specific indications for the management and optimization of the IFC model during this process.

It is not purpose of this paper to describe in detail the content of these recommendations, which are intended to be published as a part of a BIM-based integration of the already issued Guidelines for Energy Audits of Buildings (UNI/TR 11,775). The aim is rather to explain the methodology that has led to their definition and the general rationale of the research.

2.2 From Energy Analysis to BIM: Customized Property Sets (Pset) for Energy Analyses

The second phase of the research reverses the perspective and focuses on the possibility to include, as part of an IFC model of the building, details, and results of the energy analyses carried out in the BEM software. The main results concern data about the current energy consumption of the building, energy performance indicators correlated to building features (areas, volumes), and proposals for improving energy efficiency and calculating the resulting savings. Such information is traditionally organized in specialist technical reports and attachments to be shared with the client.

Among these is the file processed within the energy analysis software used, which is only readable by those who own the specific software. With this approach, the work of the energy auditors is not fully valued, also in relation to the great potential of BIM for greater knowledge and for the digitization of the existing building stock.

The BIM model is indeed a container of information that, through export to IFC, become readable by all the actors involved in the process, regardless of the software that produced them. Hence, it is the IFC file of the model, adequately enriched with the details and results of the energy analyses, the right tool to value the work of energy auditors. However, the analysis of the IFC file exported from the energy analysis software used on a case study showed that it includes only the geometric characteristics of the building, with some thermo-physical information related to the building components. The need to expand what of the energy performance analysis is exported to the IFC file is evident for maximum fruition of the audit outcomes.

Accordingly, the second phase of the research has focused on the definition of a list of quantitative and energy parameters to be associated with the as-is BIM model, with the aim of returning the results of an energy audit. This is essential not only for a correct and complete description of the building being analysed, but also for the possibility to “catalogue” the existing building stock according to specific energy parameters. User-defined Property Sets (Psets) were used to implement these contents within the BIM as-is model. Properties are directly linked to the IFC Building entity and grouped into two Psets:

  • Building Quantitative Data: containing the data of the building that are used to identify the heated net and gross surfaces and volumes, the surface of the dispersant envelope, on the basis of which the main energy performance indicators are also calculated;

  • Building Energy Data: containing the results of the energy inventory and performance calculations (performance indicators, energy consumption, expenses per energy carrier…).

Psets can also include a link to the whole energy audit report, which also contains the proposals for improving the building performance and energy saving. For the mapping of these properties, it has been referred to ADM (2021).

It is not purpose of this paper to list all individuated properties (Centi and Morini, 2021), but rather to explain the approach, its possible advantages and uses. First, the definition of these Psets can represent a guide for contracting authorities in defining the information requirements for energy analyses in BIM-based tendering. They can also serve as a checklist by BEM software companies to identify the information to include in the IFC files after an energy analysis. The possibility of automatically exporting all the parameters and thus of having an IFC file complete with the results of an energy audit could greatly simplify the integration of the auditors’ work into the BIM process.

Figure 6.2 schematizes the process of the second phase of the research, going from the energy analysis software to the “enriched” IFC model (shown in Fig. 6.3): all the information content about the building is stored in the agreed CDE for its future uses (among which is the project of the proposed energy efficiency measures).

Fig. 6.2
A flow diagram has four levels. Level 1 of the B E M software has energy, performance, efficiency, and savings analysis. Level 2 of B I M viewer has a compilation of I F C parameters. Level 3 of B I M authoring software has parametric modeling, and level 4 has a common data environment.

Process from energy analysis to BIM

Full size image
Fig. 6.3
A screenshot of an I F C model has a browser and element toolbar on the left and a property toolbar on the right. The middle panel has an irregular 3-dimensional structure with projected lines and a few patterns on the front.

(Source Karlsruhe Institute of Technology)

Screenshot of a BIM viewer displaying an IFC model enriched with the defined Psets

Full size image

A possible continuation of the research activity, in the direction of the maximum interoperability of energy audit in the BIM environment, could consist in the identification of correspondences of these parameters within the IFC standard according to the indications of the buildingSMART committee and the proposal of new parameters to be implement at the standard level. However, most of the parameters identified refer specifically to the energy calculation method contained in the relevant Italian standards, and therefore, they make it necessary to use custom Property Sets (Pset).

3 Conclusions

This paper proposed a BIM-based approach to energy analysis of existing buildings in the Italian context. It briefly covered the whole process without getting into the technical details of it, but providing an overview of the research methodology, its objectives, and its main outcomes. Both the modelling recommendations for maximum interoperability between BIM authoring and BEM software and the list of customized Psets for energy analyses will be made available freely to the public. In particular, they could be included in a future version of the Guidelines for Energy Audits of Buildings, implemented within a BIM perspective, in line with the aim of this work, i.e. supporting professionals and enhancing the adoption of BIM in the refurbishment of the existing building stock.

The recommendations will be aimed at simplifying the work of the auditors by identifying general modelling actions, which can reduce errors and loss of information when importing the model into the analysis software. These aspects hinder the full use of BIM for energy analysis as well as the exploitation of its potential. On the other hand, the recommendation will also aim to draw attention on problems that cannot be solved “simply” through modelling and thus require solutions either at a software or standard level, stimulating the search for shared solutions, which could form the basis for future research developments in this field. For example, the study of these recommendations may be also useful for software houses for the optimization of some of the identified issues. In parallel, a codification of user-defined Psets to be associated with the as-is IFC model of a building was put in place with the aim of returning the results of an energy audit within an interoperable model. This also means making the work of the auditors easier to consult and utilize for planning and carrying out the proposed interventions, for the future management and maintenance of the building as well as for a more in-depth knowledge of the building. The wide diffusion of these energy parameters at national level could give a great impulse in this sense, overcoming the intrinsic limit linked to the use of user-defined, and not of common, Psets. This will be possible through the publication of the guidelines referred to in this work and their adoption as a technical-regulatory reference on the national territory.

On the other hand, this will also be possible through the implementation by the software companies of these parameters—mapped according to the proposed scheme—in the IFC files exported from the applications for energy analysis on the Italian market.