CITA BIM Gathering 2015, November 12th -13th 2015

Development of a Model View Definition for Environmental and Energy Performance Assessment

Sérgio V. Pinheiro1, Edward Corry2, Paul Kenny3 and James O’Donnell4

School of Mechanical and Materials Engineering, School of Architecture and UCD Energy Institute

University College Dublin, Dublin, Co. Dublin

E-mail: 1sergio.pinheiro@ucdconnect.ie 2edward.corry@ucd.ie3paul.kenny@ucd.ie 4james.odonnell@ucd.ie

Abstract – Very often, building managers face the challenge of having to operate a building in the absence of the appropriate information about how it should function. This problem is one of the many reasons why buildings operate inefficiently and tend to consume excessive amounts of energy. Building Information Modelling (BIM) is an emerging technology which addresses the management of information throughout the Building Life-Cycle (BLC). Industry Foundation Classes (IFC) is a non-proprietary data model of BIM that enables effective data integration over the BLC. IFC is a rich data model which may represent the entire building, however most applications are interested in a subset of this model. Hence, it is necessary to filter the information exchange between different applications and Model View Definitions (MVD) is the methodology to define such subsets. This paper presents the development of a MVD for environmental and energy performance assessment to support building managers during operation.

Keywords – MVD, IFC, BIM, Environmental and Energy Assessment.

I INTRODUCTION

It is widely acknowledged by industry and research organisations that buildings operate inefficiently [1]. They consume nearly 40% of the total primary energy in the world and are responsible for around 30% of the total global CO2 emissions [2]. Some studies also show an expected increase of 50% in energy demand in buildings between 2010 and 2050 in a business as usual scenario. However, following an energy efficient and low carbon pathways could lead to 25% reduction in total energy use compared to business as usual [3]. Reduction in energy consumption in the building sector is vital to any long term strategies. Legislation, environmental concerns, financial issues also influence organisations to reduce their energy use [4].

More than half of the current building stock is expected to still be operational in 2050. Considering the lifespan of buildings, actions cannot be limited to tighter controls on new constructions [3]. Increasing demand for building services and comfort levels, together with the rise in time spent inside buildings, assure the upward trend in energy demand will continue into the future [5].

For most buildings, the majority of energy use is in the operational phase and energy conservation efforts have appropriately focused on reducing this energy use through smarter design and improved building technology [6].

Building Information Modelling (BIM) is an advanced information technology that is becoming widely adopted in the AEC/FM (Architecture, Engineering, Construction and Facility Management) industry. BIM is a process for managing the information produced during the design stage throughout the Building Life-Cycle (BLC), in a common format, in order to enable the best and most efficient use of the information [7]. The Industry Foundation Classes (IFC) is the most widely adopted common data format in the BIM environment.

IFC uses an object oriented description to ensure consistent data exchange and interoperability between several applications. It enables sharing of properties of building elements to support decision making in different stages of the BLC. Most modern BIM authoring platforms support the import and/or export of IFC model data. This flow of information is critical for collaboration and interoperability

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because it connects different downstream applications, such as facilities management, structural modelling and performance analysis applications [7].

The IFC schema can be used to model all building components, however most stakeholders and their applications have an interest in a limited area (subschema) of this complex schema. Hence, the exchange of information between applications must be tailored according to domain specific Model View Definitions (MVD). Traditionally MVD was used to define an exchange of IFC data that would meet the end user’s need and implement methods of exchanging data between software applications.

The MVD proposed for this paper contains the exchange requirements necessary for environmental and energy performance assessment. This exchange of information should provide clear and consistent information to building managers, to enable more informed decisions. The final goal of this work is to support the efforts of the building manager at different stages of the BLC in the reduction of building energy consumption, without compromising environmental performance. This methodology also supports the building manager to determine the most effective building operation strategy. The following section explains what a MVD is and how to define one. Section III defines the exchange requirements necessary to perform

environmental and energy assessment. These requirements are used in the process to develop a MVD for performance assessment, as described in Section IV. Finally, Section V discusses the limitations encountered in the process, while Section VI concludes the presented work.

II BACKGROUND ON MODEL VIEW DEFINITION

Building managers often face the issue of model exchanges being incomplete or error prone due to the lack of semantic definitions within IFC [8]. IFC is a rich product modelling schema, offering multiple ways to define objects, relations and attributes [8]. These different ways of defining the same data led to the development of domain specific MVD to define precisely how building model exchanges should be expressed using IFC.

The first MVD developed by buildingSMART is known as Coordination View. The main purpose of this view is to allow sharing of building models between the major disciplines of architecture, structural engineering and building services (mechanical) [9].

An MVD is considered a subschema of the IFC specification. The purpose of this subschema is to select and specify the appropriate information entities from a schema, their attributes and rules that

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Fig. 1: MVD format overview [23]Fig. 1: MVD format overview [23]Fig. 1: MVD format overview [23]Fig. 1: MVD format overview [23]Fig. 1: MVD format overview [23]Fig. 1: MVD format overview [23]

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govern their possible values for particular uses [10]. The selected entities that define a MVD are a subset of all those in the original IFC schema.

The first step of the process in defining a MVD is to identify the scope of the information exchange between one or more stakeholders. For each set of information, the functional requirements to be exchanged are defined as Exchange Requirements (ER). These ER are later structured into an Information Delivery Manual (IDM) representing a standardised methodology that provides a universal, repeatable and verifiable method for creating information exchange.

The ER defined in one or more IDMs is organised into a set of information modules, named as MVD Concepts. MVDs are usually represented diagrammatically, as shown in Fig. 1. The ER share the same IFC independent requirement definitions format with MVD. This makes it easy to merge several ERs (which define data exchange between stakeholders) into one MVD (which defines data exchange between software applications).

The development of MVDs follows guidelines provided by buildingSMART International [11]. The basic structure of a MVD includes a set of concepts, which reference a specific IFC entity. Each concept defines a graph of entities and attributes, with constraints and parameters set for particular attributes and instance types. Concepts are backed up by templates to uniquely describe the components of a MVD [12].

The format for MVD diagrams and configuration is defined by an XML schema, known as mvdXML. This schema makes extensive use of two general ideas: Definitions and Configurations, which combined create one MVD. Definitions capture a range of concepts and represents them and their relationship in the context of the diagram, while Configurations capture how those concepts are used in a specific case (Fig. 2).

Configuration ‘N’Configuration #2Definition

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Fig. 2: The use of Definitions and Configurations to create MVDs [11]

This type of representation allows one single

MVD to contain all the exchange requirements within scope, with the advantage to choose which of them are necessary to satisfy a particular business process reducing the scope of it. Another approach

to reduce the scope of a MVD is the application of Business Rules (BR).

For example, BR can be used to vary the result of using an information model (e.g. IFC data model) without having to change the model itself. They provide flexibility for the model through the application of different sets of rules to the same information model. A practical example of a BR might be: “the humidity of an office must be less than 70% and greater than 30%” [13]. In this form, when applied to a concept, a logical assimilation is associated with the manner in which the attribute/property is created.

a) mvdXML SchemamvdXML refers to an electronic format for representing MVD. It is a generic structure that is applied to the IFC data schema. According to [12], this format serves several purposes:

- To support automated validation of IFC datasets

- To generate documentation for specific MVD- To support software vendors providing filtering

of IFC data based on model views- To limit the scope of IFC for particular

business process.In order to provide consistent and a computer-

interpretable definition of MVD, buildingSMART International created the IfcDoc tool [14]. This tool is based on the mvdXML schema which aligns to IFC EXPRESS schema. The IfcDoc tool is used to generate documentation of the IFC specification itself and the baseline MVD concept templates. It allows it to quickly expand the generic MVD concepts to cover the specific requirements and business rules that are introduced by a set of exchange requirements.

III EXCHANGE REQUIREMENTS FOR ENVIRONMENTAL AND ENERGY

PERFORMANCE ANALYSIS In recent years, the environmental and energy performance of a building has emerged as an important topic in the AEC/FM industry. The peak load and electricity demand of buildings are increasingly scrutinised in order to reduce fossil fuels consumption and satisfy legislative requirements[15].

Tools such as Building Management Systems (BMS) that control systems operating status and Energy Management Systems (EMS) that display energy consumption help building managers to safely and efficiently operate the building. However, the information provided by these tools is not as reliable as it should be [4], thus an absence of structured information in the provision of optimally performing buildings is present during operation.

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Ideally, building managers require a set of performance specifications that represent building performance. This type of information is created during the design stage and is known as design intent. The design intent contains all the performance specifications of the building and serve as a baseline for future performance assessment. New practices use energy prediction modelling to check building performance efficiency, thus enabling building managers to compare actual performance against expected design intent.

The gathering of specific performance specifications is a time consuming process for building managers, where in many cases the information requested was lost during the handover process or was not well documented. Unavailable, unreliable and inaccurate information is a major cause for inefficient building operation [16].

Building operation requires managers to understand a building’s function, defined as a controlled environment for a predefined purpose [16]. For this reason, building function is of paramount importance for most performance analysis and is therefore a priority for building managers.

Existing tools and techniques for monitoring building performance fail to demonstrate the relationship between building function, energy consumption and associated environment impact in a manner that allows building managers to make actionable decisions [4]. A new approach to solve

this problem is the integration of BIM with predictive modelling tools such as EnergyPlus or with Building Management Systems.

BIM supports building managers, providing direct access to the information they require to make more informed decisions. BIM enables collaborative working processes (Fig. 3) and acts as the central data repository from which all project stakeholders can have access to the same information at the same time. BIM can represent very large data sets, however, only part of this data is applicable to performance analysis. The choice of specific data from BIM focuses on two main aspects of building performance: environmental conditions and energy consumption.

a) Environmental ConditionsMaintaining constant thermal conditions during operation is one of the main tasks facing building managers. Even minor deviations from static comfort levels may be stressful and affect an occupant’s performance and safety. Furthermore, temperature preferences can vary among individuals and there is no temperature that can satisfy everyone. Adaptive comfort models deal with the human behaviour taking into consideration that people will generally change their behaviour accordingly to the changes in the thermal environmental.

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Fig. 3: Collaborative process for information exchange between stakeholders to define optimum operationFig. 3: Collaborative process for information exchange between stakeholders to define optimum operationFig. 3: Collaborative process for information exchange between stakeholders to define optimum operationFig. 3: Collaborative process for information exchange between stakeholders to define optimum operationFig. 3: Collaborative process for information exchange between stakeholders to define optimum operationFig. 3: Collaborative process for information exchange between stakeholders to define optimum operation

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Extensive laboratory and field data have been collected, which provided the necessary statistical data to define conditions that a specified percentage of occupants will find thermally comfortable such as Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD). According to [17], there are six primary factors that must be addressed when defining conditions for thermal comfort:

- Metabolic rate (M)- Clothing insulation (clo)- Air temperature (⁰C)- Radiant temperature (⁰C)- Air speed (m/s)- Humidity (%)

The failure to meet the recommended thermal comfort levels can have negative consequences on occupant productivity [18]. Since personnel costs dominate all others related to building operation by two orders of magnitude, a comfortable workplace is of the utmost importance for the economic success of companies [19].

Thermal comfort has a significant influence in determining the energy consumption of a building’s environmental system [20].

b) Energy PerformanceTypically building managers expend a minimal amount of time focusing on improving energy consumption due to loss of data and fragmentation of information [4]. Building manager’s requirements consist of a set of control parameters that are used in the operation strategy of the building. Usually these parameters come from prescriptive code compliance, energy performance guidelines, energy simulation models and performance benchmarks.

The European Commission published in 2002, the first Energy Performance of Buildings Directive (EPBD) [21], with a further revision published in 2010. This Directive has the potential to be an important instrument in motivating all EU member states to achieve higher building energy performance. The EPBD established a set of minimum requirements to perform energy assessment in new and existing buildings. However, energy performance from a building manager perspective covers much more information than the one established by EPBD, such as:

- HVAC schematics, specifications and schedules

- Design intent

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Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

Fig. 4: Process of information exchange using the MVD methodology to support environmental and energy assessment during operation

CITA BIM Gathering 2015, November 12th -13th 2015

- Building Management Systems (BMS) specifications

- Operational & Maintenance manuals- BMS alarm records- Building performance history, etc.

A complete list of the building manager requirements are described in [4].

These requirements take into account the general indoor climate conditions, in order to avoid possible negative effects such as inadequate ventilation, poor environmental conditions and designated function. The grouping of these requirements defines the Exchange Requirements (ER) for environmental and energy performance analysis. The requirements described above are the minimum parameters, but analysis is not limited to them.

During operation building managers suffer from the lack of a specific set of performance requirements to efficently operate buildings. A need to explicitly capture the exchange requirements is the main motivation for the development of a MVD for performance assessment.

By doing so, building managers can easily retrieve the required information to conduct their analysis. This approach reduces the time that building managers spend trying to find and extract the required information. It also helps building managers to focus on improving building performance reaching optimum operation.

IV DEVELOPMENT OF THE MVDThe proposed MVD for assessment defines the exchange requirements required by building managers to assess operational performance. It represents the information to be exchanged between two or more stakeholders in support of a particular business process at a specific stage of the BLC, as shown in (Fig. 4). It is important to understand that these requirements come from the end user’s need

and the primary role of the IFC model view is to ensure IFC implementation supports these requirements.

The first step in the creation of a MVD is to map the ER to IFC entities. This process requires a deep knowledge of the IFC schema. The IFC documentation, available in the buildingSMART website [22] helps the mapping process. This document contains the specification of the IFC standard and consists of data schema, represented as EXPRESS and XML schema specification, and includes terms, concepts and data specification items as defined by the AEC/FM industry.

After finishing the mapping process the next step is to use the IfcDoc tool [14] to create the MVD itself and generate its documentation. Previous attempts at defining MVDs used templates to generate the diagrams manually, but since IfcDoc was published all the documentation is automatically generated by this tool. The documentation generated is in HTML (HyperText Markup Language) format and serves as the basis for vendors to implement export and/or import functions in their software.

For instance, if a BIM software has already implemented a MVD to support a specific business process, the output IFC file will contain only the exchange requirements defined for that particular analysis reducing the amount of irrelevant information. By providing building managers with this type of clean information, they can now start to focus on improving the efficiency of the building. This approach, in theory, reduces the time necessary to collect the information from the previous stage of the BLC. A small demonstration of the creation of a MVD is presented in the next section.

a) Demonstration In order to reduce the level of complexity only one set of exchange requirements is examined in this demonstration: that relating to indoor air

Entity Model View Definition Exchange Concepts Instance Diagram

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

Fig. 5: Example of an instance diagram of the IfcSpace entity assigned to different MVDs containing several MVD concepts

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temperature. Indoor air temperature is a key factor that needs to be monitored inside a space in order to maintain appropriate environmental conditions and is directly related to the energy consumption due to the HVAC and related systems. Spaces are occupied areas or volumes that provide certain functions within a building. The mapping of the exchange requirement “space” to IFC specification is IfcSpace.

For this demonstration the IfcDoc tool is used to create the instance diagrams of a MVD. As shown in Fig. 5, the entity IfcSpace can be defined in different MVDs (highlighted in yellow). For each MVD a set of concepts (highlighted in green) are applied according to the exchange requirement of a particular process. Technically, concepts are independent of any IFC Model View Definition, which makes it possible to re-use the same concept even when the IFC model specification changes.

This example is only one entity and the final MVD for environmental and energy performance assessment will contain all the exchange requirements and their relationships. The main purpose of this MVD is to support building managers to assess the building during operation.

V LIMITATIONS AND DISCUSSION The IFC schema is the standard for information exchanges in BIM. It is a rich model that addresses the needs of different disciplines and provides a variety of ways to define parts of a building. Hence the use of model views to explicitly define IFC implementation is required. One of the main issues with this methodology is the possibility to duplicate previous information already defined in another MVD. In this case, both MVDs should be joint to create a new MVD with a large scope.

The introduction of MVD concepts to the methodology brings more flexibility and modularity when dealing with MVDs.

One of the main limitations encountered by the authors of the paper is the lack of publications and demonstration related to MVD. Although many industry and research groups are developing MVDs for different applications of the AEC/FM information exchange, only a few MVDs are available for reference.

VI CONCLUSIONS This paper presented a methodology to support building managers in specifying and analysing building environmental and energy performance. The idea behind this approach is to capture the building manager requirements and address them using the MVD methodology. This approach offers the opportunity to export IFC files according to the building manager’s requirements defined in the MVD specific to performance analysis.

The MVD presented in this paper is still at an early stage of development. A full demonstration of the potential of this methodology is planned after the completion of the MVD for environmental and energy analysis. If the results from this test are as expected, the MVD will be submitted to buildingSMART International to become an official MVD.

ACKNOWLEDGMENT

This work was supported by a Marie Curie FP7 Integration Grant within the 7th European Union Framework Programme, project title SuPerB, project number 631617 and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) under the program Science Without Borders.

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