2.1. Planning Process
A systemic, holistic mindset stood at the root of the idea of integral planning that originated in the context of increasing ecological awareness in the course of the 1960s and 70s [18
]. In the field of building design, integral planning is often required if a complex construction project is to be optimally implemented taking into account all aspects of building construction and building technology. With the aim of drastically reducing the energy consumption of buildings, this paradigm also established itself in standards, in Switzerland, for example, with the SIA performance model 95. Even if there is no unified definition of integral planning today, its application usually contains horizontal integration and vertical integration [19
]. Horizontal integration aims to optimize the interaction of the subsystems of buildings (focus on system technology), and vertical integration takes into account environmental, economic, technical, functional, and social issues. These differ over the entire life cycle of the building with a focus on the aim of a sustainable building [20
Here, throughout the planning and construction process, specialist planning has to be integrated by the main design process and share a common effort in order to achieve high quality of buildings. Because of specific needs of information structure within specialist software tools and missing uniform interfaces, up to now, model-based data, as derived from architects’ coordination models as the base of specialist planning, mainly, have to be remodeled from scratch, with great effort. Adding to this, a corresponding susceptibility to errors and the time required for data input are found that limit the use of specialists’ software and assessment as an accompanying tool, in the early planning phases, for optimizing the building design and examining variants of various basic concepts. In addition to enhancing the data flow with correspondingly optimized workflows on a technical level, the normalized integration of information structures, for input and result data on the side of the specialist planning facilitated by standardized open data formats, can also build a solid contractual basis. Thus, the original purpose and application workflow of specification standards, i.e., model view definition (MVD) in the norm-based framework of information delivery manuals (IDM), which are also elaborated on their technical side in the following section, has been extended in current praxis. From its native (technical) use case, to ensure quality of data interface implementations in software tools, this is now also implemented and, for example, already requested from German authorities in the context of client information requirements (Auftraggeberinformationsanforderungen, AIA) that are integrated in the treaty framework of respective BIM execution plans (BEP) [21
]. Together, these newly established methods build a suitable process environment in which the (technical) implementation of solid model-based workflows among cooperating partners by means of BIM can be embedded [23
]. Here, in a secured frame of self-defined structure, in terms of data quality through the a priori specification, all exchange processes in the project can contribute to a benefit thereof [22
]. Currently, it can be observed that every discipline as part of the planning, construction, and operation of the built environment develops respective new workflows on data handling in the context of its digitization effort, and thus can be integrated with an overall model-based planning which helps to unlock the (full) potentials of BIM. As implied by the integral planning, the aim of process accompanying, iterative optimization of the digital planned object before its construction is at the core of these efforts at the process level [24
]. Therefore, it achieves higher quality buildings regarding the specific aspects of the respective specialist discipline being integrated in the overall planning process, for example, building performance simulation (BPS), and also infrastructure planning, as well as regarding urban planning, i.e., the energy simulation of districts [22
In the field of LCA, there is a need to carefully analyze how and when respective specialist planning information enter into the overall planning process. Despite a lack of well-documented practical experience, many approaches claim to harvest the benefit of integrating LCA in the “early” planning stages where it offers the most impact on the later building at the least cost. Here, studies show that due to not being properly defined, the term “early” seems to be applied ambiguously [2
]. The point in time when the decision maker can make use of decision support is crucial as it determines the data setup regarding given information, as well as the LCA methods that can be employed together with the incorporated uncertainties [31
]. Thus, many of today’s approaches lack comparability with each other and also lack possibilities of scaling or transferability to other contexts [17
]. The process accompanying approach presented in this paper, therefore, applies coarse LCA benchmarks on a building scale for initial decision support that successively decompose alongside the process into a more detailed LCA as information levels increase, for example, for types of building elements in order to address decisions on alternatives (Figure 1
]. In later planning stages, when the decisions with the highest environmental impact are determined, the approach considers the fine granularity of available data, as well as the most specific detailed LCA data on building components and materials which are already being used in practice for preparing specific building certification.
2.2. Technical Interfaces
BIM is a widely applied workflow in the building sector providing the basis for digital architecture. It aims to enable the collaboration of all involved actors in the planning and design process, through providing accessibility for all, to one single digital building model.
Dealing with the increasing demand for information exchange in digital architecture, the necessity to transfer the planning process from a limited digital working environment (referred to as closed BIM) to an open BIM workflow is of great importance. In closed BIM, the planning actors work simultaneously on the same building model created in one (proprietary) data format, which is possible only when supported with programs by applications of one vendors’ software family. Hence, these closed BIM workflow environments do not allow any flexibility for the relevant partners in using vendor independent software that, especially in terms of expert application, does not support proprietary data models of several vendors. Being advantageous when the same team of different planners originates in a single firm, it represents a challenge for the exchange of design concepts with external partners, especially in the case of public buildings [6
]. The implied reluctance in implementing these closed BIM workflows can be observed well in the German market situation that traditionally consists of many smaller planning firms joining together differently on every project, and thus prefers open data exchange as the basis of collaboration [23
The benefits of planning based on open BIM, are expressed in the flexibility of data, traffic with the application of neutral data formats such as IFC, BCF, COBie, CityGML, gbXML etc. that enable data transfer among programs of different vendors and, consequently, the export and import of data in adaptable and compliable data formats for each specific BIM software (i.e., NEMETSCHEK and GRAPHISOFT) [35
On the basis of open product models, a methodology has been established in recent years under the term (open) BIM, in which the a priori specification of planning data (as well as their structures and qualities) enable standardized data exchange within the planning process [37
]. Open BIM relates to and requires the collaboration of involved actors based on vendor neutral data-exchange formats determined by buildingSMART International [36
]. A model-based working method is required to map consistently the planning object over the entire planning process in digital three-dimensional building models with stored semantics. The data to be exchanged among the partners within the scope of planning cooperation, such as specialist planning prepared by experts, then, is specified as a partial image of an overall model and the quality to be delivered is determined before the order is placed. The contractual basis for this is provided by the so-called client information requirements (AIA), which use references to the open model language IFC as the basis for the concrete specification of which data is to be supplied. In order to provide a formal framework for this specification, the information delivery manual, which originates from standardization work, is used with the formal IFC specification language model view definition (MVD) [22
]. Initially, these IDMs were used to uniquely specify parts of the IFC that were required for the certification of IFC interface implementations in CAD platforms and authoring tools. With the increasing establishment of the BIM method, these methods and standards in the IFC environment play an increasingly important role in holistic data management.
The formal framework for creating an information delivery manual (IDM) is described in DIN EN ISO 29481-1 [38
]. The standard stipulates that, for a particular business context, the specific cases of information exchange must be specified with an IDM in the given form. The last version of this standard from 2016 was supplemented and sharpened by further guidelines and templates in the context of its application in standardization and standardization work (see bsDE User Manual, IDM Word template, as well as VDI 2552 part 10.1 [39
]). Therefore, a consistent set of tools is available for the standards-based specification of the basis of an IFC model view of a specific data exchange context. This set of tolls was also used in the research project which this article has been based.
An IDM serves to provide an unambiguous representation of the information to be exchanged against the background of a business context to be determined, such as the exchange between the coordinating architecture and a technical domain. After a preliminary definition of the scope of the IDM and the involved roles for the data exchange with the business context, a first main part of the project clarifies the exact process flow of the individual data transfers in the planning phase. Standards-based process diagrams using the diagram language Business Process Modeling Notation (BPMN) specify the exact data transfer points between role-based actors. Respectively in these points, the exchanged data is specified in tabular form in the second main section. A given table structure, first, requires the specification of a reference object, such as the building or component object, before successively nesting a characteristic concept or group, and then the requested characteristics of the data record to be exchanged (data drop). In addition to the natural language definition of the reference object, concept, or characteristic, each entry in the structured table must be marked to indicate whether it is mandatory or optional for the data exchange.
For the context of developing the IFC standard, different working groups apply the IDM methodology within the standardization body of buildingSMART for collecting information demands of different disciplines in the field of architecture, engineering, construction, and operation. Here, the intermediate goal is to provide suitable model view definitions (MVDs) that can serve the different observed data exchange scenarios. In a long-term perspective, the single views also contribute to the overall optimization of the IFC standard itself that evolves through the extension of description concepts to better suit its application in open BIM workflows. As a starting point for gathering information demands in the field of LCA, the approach presented in this paper, therefore, begins with the application of the IDM method. Then, this builds the base for a formalized extension of the latest IFC version in the framework of an MVD in order to profit from the latest developments in the standard such as the comprehensive HVAC part introduced in IFC Version 4. As different approaches for specifying and optimizing the application of the IDM methodology are currently under development, the IDM approach followed in the underlying research project and presented in Section 3.2
is based on the lessons learned from the other approaches and supplemented with (planning accompanying) aspects as required by the LCA application context [8
2.3. Building Information Modeling (BIM) and Life Cycle Assessment (LCA)
Life cycle assessment (LCA) is a methodology developed for analyzing possible environmental impacts associated with manufacturing and consumption of products and a central instrument for the quantitative assessment of the environmental quality of buildings. The principles and framework of the LCA methodology are defined in the ISO 14040 standard, whereas ISO 14044 determines the requirements and guidelines [40
]. An LCA study includes four stages [41
], as depicted in Figure 2
. This is in the construction sector further concretized by the standards EN 15804 for the definition of core rules for sustainability assessment of construction products (PCRs) and DIN V 18599 for the assessment of building energy performance [42
]. LCA models in the construction sector are usually highly modularized due to the hierarchical structure of buildings and make use of readymade Life Cycle Impact Assessment (LCIA) results that are publicly available for generic product groups and for specific products through Environmental Product Declarations (EPD) [44
]. The methodology is contained in most certification systems for assessing sustainability, such as BREEAM, LEED, BNB, or DGNB, and the core of the emerging European Level(s) framework [45
]. The continuous update of the LCA relevant norms and standards, points out the actualization of environmental indicators, especially the increasing requirements on product environmental footprint (PEF) [47
]. The rise of requirements concerning the environmental performance, thus, leads to higher complexity of the LCA application and for full compatibility of these complex models, to planning practice [48
]. Furthermore, this results in requirements to applied LCA data regarding updatability, consistence, flexibility and digital implementability that are not yet covered by existing construction LCA data [44
]. Various SBA tools have been developed alongside the LCA methodology. Their main functions adhere to the evaluation of environmental performance for certification purposes, and some also address environmental comparison of design alternatives [49
]. Often applied on completed planning status, the required information for LCA is currently rather unstructured and transferred manually into the LCA tools [7
]. Due to the resulting susceptibility to errors and the time required for data input, life cycle assessment is rarely used as an accompanying tool for optimizing the building design in the early planning phases and for examining variants of various basic concepts [50
]. Hence, neither can the function of an LCA accompanying planning cannot be fulfilled by these approaches, nor can they take advantage of the ongoing implementation of digital methods in the field of planning (e.g., BIM) and significantly reduce the needed effort for data acquisition [48
In the last years, the integration of BIM and LCA has increasingly gained interest especially in research [10
]. The integration of LCA with BIM is an ongoing process, which is evolving in parallel with the evolution of the LCA methodology and BIM advancement [52
]. As such, this integration process is also inclined to become continuously more complex resulting in the need for standardization and harmonization of approaches. The application of standardized formats for data exchange enables interoperability throughout the planning and design process and aids the challenge of integrating LCA with BIM through space for implementing environmental impacts information in the overall data structure. The tendency of the new tools to integrate LCA information in the three-dimensional (3D) modeling process refers to the necessity from the building sector for available environmental assessment data. This issue needs to address the problems that arise due to ineffective information during data exchange or problems from insufficient data description of exchange requirements on the one hand, and, on the other hand, the need to extract environmental impact results throughout the entire planning and design process from the first stages [50
The classification scheme provided by Wastiels and Decuypere presented five strategies for BIM-LCA integration. The two most frequently applied strategies were data provision for LCA through the extraction of a bill of quantity (BoQ) and the integration of LCA with BIM through plug-ins. However, both strategies offered significant challenges for comprehensive BIM-LCA integration. While the BoQ approach significantly reduces the effort for data acquisition, there is potential for error as the information is only linked indirectly. Furthermore, the information often times does not feed back to the modeler and decision support is lacking. Up to now, plug-in strategies do not consider specific data on the LCA side and are, thus, not feasible to meet the requirements of comprehensive LCA assessments [17
]. Compared to these strategies, connecting the information demands directly to the data depiction concepts provided by BIM offers several fundamental advantages [16
]. Whenever changes are made to certain planning information, the direct linking of LCA-specific data to a given quantity set results in a direct coupling. This approach is potentially more transparent and stable than the extraction of a BoQ and more flexible than plug-in strategies. Furthermore, with increasing concretization of the planned object during the planning process, BIM models facilitate depiction concepts to structure in one BIM object.
Most certification schemes foster the use of BIM for certification, but do not support BIM-based LCA submission [54
]. In the context of a working group of the Association of German Engineers (Verein Deutscher Ingenieure, VDI), BNB and DGNB are, together with experts on BIM and LCA, actively working on a standardized interface for a BIM-based submission of LCA results [8
]. While several SBA tools offer BIM-related services, they either represent the environmental impact in a simplified manner (e.g., IMPACT), or require very specialized open BIM data. In the first case, impacts are assigned to the area of a closed BIM environment, and can only be used in design-related planning statuses (mostly add-ons to proprietary CAD systems, such as the Rhino add-on of CAALA) [55
]. In the second, often a complete remodeling of the BIM model is necessary. With respect to the digitalization of building information, the connection of data, in the context of LCA, with the data occurring in the process of planning implies the need for a common and unified data interface as a continuous database [17
]. In ökobilanz-bau, this integration is carried out through an interface with Bim2Sim, while CAALA allows CAD and BIM integration as plug-in for Sketchup and Rhino models [55
]. All existing SBA tools display environmental assessment results in certification-label templates, whereas eLCA and GENERIS®
allow the direct submission for certification [56
The fifth strategy contains workflows with a fully transparent data handling by encapsulating LCA-specific data directly in the BIM object [16
]. This integration type enables direct feedback of environmental impacts because only one data source contains all data. However, when realized through BIM objects, this information is not necessarily transparent or standardized. The BIM2LCA approach, presented in this paper, builds upon this integration type. By employing references to established external data sources, such as the data dictionary approach of buildingSMART, the approach extends these kind of integration types in order to address identified deficiency, for example, baring the risk of creating large and unresponsive files [16
]. Adding to this, the full potential of the integration type is pursued by the BIM2LCA approach by addressing the information flow of the LCA-tool results and reintegrating them with the BIM model [32
]. The implied workflow to connect BIM and LCA software bidirectionally is depicted in Figure 3
. First, the planner creates the planned object in a BIM-based authoring tool (e.g., CAD). Then, the model is transferred to the LCA system, as a second step. This includes exporting the model as an Extensible Markup Language (XML) variant of the IFC standard (IFCXML) based on the LCA MVD using a BIM authoring system, server-based referencing (materials, constructions) and enrichment (integration of generic and predefined life cycle elements), and IFCXML import of the LCA system. In an optional third step, LCA experts can adjust, complement, and specify the basic LCA input according to LCA-related requirements within an LCA expert software. This step is realized within the web software GENERIS®
, which is the redevelopment of the web tool sbs online tool for building LCA by Fraunhofer IBP. Within the software, an IFCXML-based interface has been established which will be offered as a feature in future versions [56
]. The fourth step, then, feeds back the LCA result into the BIM system through specification of results based on the use case requested in BIM, reintegration of LCA results in the IFCXML file, and import as well as result depiction in the BIM software.
The approach, presented in this paper, suggests the integration of LCA with the BIM process through the creation of data requirements structure for environmental information exchange among BIM software and SBA tools, based on IFC standard (IFC4.1). The environmental information can be broken down into different levels of development (LODs), corresponding to the phases of integral planning (IP), through a hierarchical configuration of data in the IFCXML.
2.4. The BIM2LCA Approach
The framework of the research project, which forms the basis of this contribution, applied the following methods in a structured approach. A core building block for this approach is the conception of an information systematic that contains dimensions for different phases of building planning, construction, and use, as well as data granularities that provide a demand-oriented level of detail. At the level of technical integration (see Figure 4
), the primary goal of the project is the implementation of an integrated planning process through normalized IFC interfaces for connecting LCA tools with BIM models (data input) and the preparation and configuration of the LCA result data for use in different sustainability rating systems (SBA). The developed information systematic (cf. Figure 1
) resulted from a comprehensive process analysis regarding integral planning and LCA, which was conducted as a first step, is presented below in Section 3.1
and Figure 4
By matching corresponding LCA methods, as well as the respective (granularity of) input information demands of the process-accompanying concretization stages of the planned object, the information systematic, as shown in Figure 1
, provides a fundamental reference system. This robustly connects the BIM planning and LCA-specific data in a transparent and replicable way. In order to realize a data interface from the conception of this information systematic, first, a clear specification of the exchange process is necessary to define the roles involved and their placement in the planning process. Because of these accurately pinned down points in the overall process, a data structure can be developed in order to enable a process accompanying, interconnected exchange throughout all the exchange points.
Following the norms of guidelines for these specification processes, as introduced in the previous section, the single data exchange processes should be depicted on behalf of open notations, as shown in Figure 5
. In addition to the context of the exchange in the overall process, the sender and recipient, as well as the involved information (index of data drop), are thereby defined. A seamless application of data formats is suggested based on the addressed data drops in the process depictions throughout the planning process and is supported by this specification approach. The process-related information demands are uniformly described and are taken into account by the following steps of gathering LCA-related information demands, synchronizing them, and developing a suitable structure for depicting them in an interconnected way.
Consequently, the core of the data structuring approach is to connect building-related information of varying granularity with concrete norm-based building element-specific LCA data through benchmark-based demand side information management [32
]. A two-layered specification process, thus, combines a flexible connection data object with a respective reference object in the building topology, for example, building, level building element, etc. (cf. Figure 1
). The initial LCA focus on a data structure approach, as the first development step, enabled the connection of aggregated, as well as detailed building information, with respective (demand oriented) configurable expert information related to LCA. For every exchange scenario, this could be evaluated and optimized. In the second development step, the identified and referenced data structures were normalized on behalf of the open IFC standard. Here, common building information and aggregates already in use during planning (e.g., the quantities of physical building elements incorporated in an LCA-centred data structuring approach) are matched and respective IFC-based entities are specified. For the other parts of the flexible data object, corresponding entities for IFC are defined. By extending the standard, current software applications are required to handle entities that are not (yet) part of the IFC. Thus, simplified specifications on the basis of IFC’s flexible property depiction concept are also developed as an intermediate alternative for the long-term targeted enhancement of the IFC standard. In order to support multiple application scenarios, the normalized BIM with LCA interface approach is embedded within a norm-based data matching context that involves two stages of external data. Following the data dictionary methodology, which can be connected to a BIM model via reference objects, a material classification is provided as a uniform referential backbone for the connected LCA and planning data and is realized as a first distributed dataset via web services. In addition to being able to fully depict the LCA data in a local IFC model, a second distributed data catalogue provides LCA-specific contents that can be referenced in the BIM model which are either replicate, for example, benchmark data, or relate to certain common construction types or redundant occurrences of preconfigured expert data for specific layouts. On the most detailed depiction stage (see right hand side in Figure 1
) the approach provides direct links to LCA database objects, for example, OEKOBAUDAT, items in order to have data models that comply with identified needs. These kinds of enhanced IFC models use model-based LCA data in official SBA procedures, for example, in the targeted DGNB SBA process, and thereby significantly reduce the involved effort in data handling.