Multi-Criteria Design Optimization using IFC language with Performance Analysis

Tian Tian LO1, Marc Aurel SCHNABEL2

1,2The Chinese University of Hong Kong (CUHK)1http://www.arch.cuhk.edu.hk, 2http://aurel.tk/1skyduo@gmail.com, 2marcaurel@cuhk.edu.hk

Abstract. The adoption of automatic generative algorithmcan open up great opportunities and options during designprocess. The use of multi-criteria design optimization hasbeen developed to promote integration of modelingenvironment with analysis and process control. This paperpresents the use of Industrial Foundation Class (IFC), acomputer language which allow cross platform of digitalfiles, to demonstrate the possibilities of generativeoptimization, automatically evaluating the performance ofeach option, and identifies the most viable designsolutions.Keywords. Mass housing; open building; rule-basedparametric; Open-Source Architecture; collaborative designsystem

IntroductionArchitecture has come a long way since the Vitruvianprinciple of firmitatis, utilitatis et venustatis. The advancement oftechnology and computer-aided design (CAD) hasdrastically changed the landscape of architecture design.Design time has shortened dramatically and what onceregarded as too complex for inclusion are now routineexpectations in architecture design (Augenbroe, 2001).Some of them are detailed analyses and considerations ofcomplex structural and mechanical systems, and thespecific impact of natural forces such as air flows,lighting and energy performances. Building simulations,an accurate tool to predict such complex systems(Mahdavi, Hartkopf, Loftness, & Lam, 1993), areincreasingly become important to produce effectivevisualization and in-depth analysis (Augenbroe, 2001).

Concurrent with this technological advancement,architecture design is no longer bounded by a singlediscipline or profession. Buildings are now recognized ashighly complex systems involving the interaction and

integration of multiple sub-systems from multipledisciplines and domains (Haymaker & Suter, 2006).Correspondingly, a single building project could involveprofessions from multiple disciplines, using specificsoftware useful in each domain. Consequently, efficientand accurate communication among different professions iscrucial. The concept of Building Information Modeling(BIM) and software interoperability therefore provides anew and efficient communication platform (Chuck, Paul,Rafael, & Kathleen, 2008).

With the increased awareness of the climate crisis andthe environmental impact of buildings recently, morearchitects are engaged in, or required to practice,sustainable design. Sustainable design emphasizes theconsideration and accurate quantification of theenvironmental impact of building designs, including butnot limited to energy and lighting performance. Buildingperformance simulation tools have thus become very usefulin building design, though not popular among architectsdue to their complexities (Wong, Khee, & Henry, 1999).This led to simulations being deployed mostly as post-design evaluation, where external simulation specialistsare engaged only after completion of design, andsimulation results relegated to documentation andregulatory compliance validation. The potential ofperformance simulation to inform the design process isthus not realized (Wong, Khee, & Henry, 1999). Moreover,such post-design use of simulation is not cost-effectiveas significant time, effort and expertise is required toremodel the digital design model, if one exists, into onthat is suitable for performance simulation. This tediousremodeling is one-off; any change to the original designentails more remodeling and would only lengthen thedesign process (Wong, Khee, & Henry, 1999). Anotherfactor is the direct applicability and usability of thesimulation result, which usually takes the form ofimmerse numerical data or false color image, might notdirectly enable design decisions or inform how design canbe improved. Additional post-processing, analysis, andinterpretation are usually necessary, which againrequires significant time, effort, and expertise. Suchfactors have been identified as the main obstacles to

using simulation tools in architectural design (Wong,Khee, & Henry, 1999).

In addition, architects have to deal with thedifficulties in communication of information betweendifferent disciplines (Chuck, Paul, Rafael, & Kathleen,2008). Throughout the design process, information isduplicated and communicated to different professions forreferencing and design work. Simultaneous editing amongmultiple parties increases time for cross-checking resultin extra time spent to sort out errors and filterduplicated information. Updates from multiple domains arethen needed to be re-conveyed to everyone else,complicating the flow of information and making itdifficult to check for errors and consistency whichcauses huge losses in time, effort and cost. Figure 1shows the significant difference when BIM is introducedinto the process, which streamlines design description,and communication giving architects more time for design.Integrating the BIM approach into simulation processescould thus provide architects easy access to simulationduring the designing phase.

Figure 1BIM Impact (Vladimir Bazjanac, Lawrence Berkeley National Laboratory, University of California, 2008)

This paper aims to examine the link between BIM andsimulation tools, and explore the possibility ofproviding an effortless and smooth transition from designmodeling tools to performance simulation tools. At theend, this paper will demonstrate the possibility ofdesign optimization via prototype software, byparametrically generating design options and evaluating

and identifying the most viable solution based onperformance-driven functions.

Performance Based Design and its RoleWith the increasing public awareness in sustainableissues, design optimization becomes very useful to findout the optimal building performance, the highestreliability and / or lowest cost of a building project.Performance based design includes different fields suchas lighting, heating, cooling, acoustics, structure andschedules. As the demand for housing and buildingsincrease dramatically over the years, optimization forperformance-based design becomes of utmost importance.

BIM are slowly becoming a major player in the industry.This ideally allows a single set of building informationto be transferred among different professions. In thisway, duplications of information that could causemiscommunications are avoided whenever changes are to bemade, which are previously inevitable and usually resultsin wasted time, resources and ultimately, loss inrevenue. With the advance technology and high-speedbuilding industry, time is one main aspect that developerwould not want to waste as it would also mean a huge lossof money (Chuck, Paul, Rafael, & Kathleen, 2008). Andwith the issues of global warming and carbonconscientiousness, an over-use of resources would makethe building non-ecofriendly or fail the green buildingrequirement, which would in turn lose its value to thepublic.

The introduction of performance based design andsimulation and with the increase of simulation programs,BIM and interoperability faces new challenges. Buildinginformation will not be complete with only mechanical,structure and design information. They are to includespecific detailed data like model location, weather data,suggested activities within each space, the specificzones of the spaces and most importantly the propertiesof the materials used in the construction. The moredetail the model is, the more accurate the simulatedanalysis is in reflection of the real situation (Figure2). This allows the architect or designer a betterunderstand of how their architecture is reacting to the

surrounding. With the detailed information, the architectcan then try other ways to improve their design in termof performance.

Figure 2Simulation models with varying degree of information

BIM is also importance as it allows the architects tokeep track of every aspect of the building. Informationlike the layers of the materials within a wall will beavailable within the same set of model. A spreadsheetlisting the amount of spaces, windows, furniture, etc canbe obtained with ease. With this, architects can pin-point errors instantly without the need to look throughevery drawing each time.

BIM is able to incorporate all information required byindividual professions, extracting them whenevernecessary. Any changes made to one set of information,will be simultaneously updated on the main BIM model andnotify the rest of the project members. In this way,manpower can be directed away from manual synchronizingof drawings, preventing drawing inconsistencies.

Each discipline involved in the same project canextract not only specific information from a single BIMmodel but also subject the model to run simulationprograms such as Fluent for M&E engineers, Autodesk Structuresfor structural analysis and Ecotect for energy analysis(Caldas & Rocha, 2001).

With so many different programs used for differentpurposes, the digital models must have the ability to beexported and imported to any other programs in order tobe efficient. Interoperability therefore becomes criticalin allowing smooth transition of files from one programinto another without losing information. To do this,conceptual schema like the Industry Foundation Class

(IFC) is created in order to extract information fromdigital model and import them into respective program fortheir respective uses.

BIM and IFCIFC is created by buildingSMART (earlier known as IAI) tofacilitate interoperability, to allow sharing ofinformation across organizations, departments, IT systemsand databases. IFC is a plain data model format that isnot bounded by any product or vendor, making it cost-effective and an easy storage of building modelinformation. While architectural and construction-relatedCAD graphic data are represented as 3D real-world objectsto aid communication visually among architects andengineers, IFC became a common language rich in internalrepresentations on building components to transferconsistently data between applications maintaining themeaning of different pieces of information during thetransfer between applications (Solibri, 2010).

Figure 3Object-based Relationships in IFC

The taxonomy of IFC uses the structure of arelationship (Figure 3) where different class objectshave their individual specific attributes and componentsreferred to as entities. Every class object, everycomponents, every attributes are only represented onceand presented once. The relationship IFC adopt ishierarchically structured (Figure 4). It can linkentities directly or indirectly in the form of a fatherand son relationship. A parent class (father) object hasa set of attributes that consists of certain rootinformation of the model while its children class (son)objects would inherit some or all the attributes of theparent class, in addition to its own attributes.

Figure 4Schema of IFC object

Two or more unique children can inherit the same parentclass attributes. One child can also inherit attributesfrom two different parent classes. The whole taxonomy ofIFC resembles a huge family of relationship (Nour & Karl,October 2008). Although it can be confusing andcomplicated, the whole ‘family-tree’ can be mapped outand sorted by the unique identity of objects, allowingthe relationships be seen clearly and ease of subsequentinformation extraction. This is possible since everyindividual entity only appear once (Figure 5).

Figure 5Schema of an IFC object (Filtered)

However, certain information in IFC cannot be extractedas they are sometimes derived from a few class objects.For example, the volume of a space is derived from theinformation (length and height) of the wall enclosing thespace. Also, they have this component ‘inverse’ exist inIFC, which mean that the information is reverse cross-referenced between entities. In other words, they do notexist in IFC and one have to implement it themselves ifneeded (Nour et al, 2008).

Generative toolsCurrently, performance based simulations only provide aninformative platform for the architects to understand howthe building react to the natural environment. It doesnot provide any kind of solution to the architects. Thus,the integration of design modeling tools and performancesimulations demands for a further development, whichcalls for this new platform named GenerativeOptimization. It not only runs performance basedsimulations, but by using pareto efficiency as basis ofanalysis, the prototypical software could also generatemultiple alternatives to the set of parameters, henceproviding a more specific and optimized solutions to thearchitects as compared to the regular human thinkingcapacity.

This paper looks at the opportunity to put generativeoptimization as part of the BIM cycle. As generativeoptimization requires smooth interoperability for the

simulation to work effectively to generate optimizedresults, this dissertation will explore the ability tosmoothen the transition from typical modeling program toperformance simulation program using one schema through aprototypical-software.

In order to better understand how to create a smoothtransition for simulation, a gap analysis between schemasand programs is important. In this case, RevitArchitecture is chosen as the modeling program due to itsability to input some implicit data into explicitcomponents and EnergyPlus as the simulation tool since itis one of the most user-friendly yet accurate simulationprogram. The IFC schema would be the interoperabilityplatform to bridge between the two programs.

The general ideal workflow (Figure 6) of the entireprocess is summarized below to give an overview to theobjectives of the entire dissertation:

Step 1 - the architect first do the building designin the digital modeling program which in this caseRevit

Step 2 - the architect designed to a certain stageand decide to run performance simulation to see howthe design can be improve or optimized

Step 3 - with just a click of a button, an applet inRevit will automatically pop up a menu that instructthe architect to input his preferred parameters andto specify the required implicit data that is neededto run the simulation

Step 4 - the simulation is run and the programautomatically create result data with alternativedesign generated visually for the architect tounderstand how his design can be improved

This ideal flow however requires trivial logisticalprogramming in order to work. In step 3, the automaticflow of Revit model to simulation program need to gothrough the process of extracting the model informationinto IFC schema and then converting the IFC file to IDFfile, the specified file format for EnergyPlus will thenrun the required simulation and generates the result.

This result will then be automatically converted intographical data for easily analysis and also optimized toa few solutions that will be converted back to IFC format

and imported back to Revit architecture, to be presentedgraphically for easy understanding.

Figure 6Ideal Workflow

In other words, the ‘behind-the-scene’ process will beas follow:

Step 1 - the model is created in digital modelingprogram, Revit Architecture

Step 2 - building information is extracted byexporting the model into IFC file format

Step 3 - a gap analysis is done to compare thedifference between IFC file format and IDF fileformat

Step 4 - the differences will then be analyzed andsplit into 2 different categories; to be defined bythe architects (like spatial usage schedule) or tobe done automatically (thermal properties and HVACsystem details)

Step 5 - a converter is created in order to filterthe information out from the IFC file format andconvert it into IDF format

Step 6 - a GUI (graphical user interface) is createdto guide the architects in entering the necessaryparameters and data

Step 7 - a program is created to run the simulation.By inserting the optimization function and usingpareto efficiency as basis, the simulation isperformed a few times to obtain a few optimizationresults

Step 8 - as the original result will be in tableform, consisting of statistical numbers which isdifficult to understand, another program extensionis needed to convert the table to graph in order toperform the data analysis

Step 9 - lastly, is to convert the IDF file formatback to IFC file format, which would be importedback into Revit for visual representation of theresult

Designing ExperimentIn architecture, there are many components which can bevaried and each project is different from one another.For this dissertation, a few parameters are taken asbasis of testing in order to prove that the program worksand that result can be obtained visually.

The most direct parameters would be the window size andposition. There are also the parameter which affects theoutlook of the building and the comfort level of theinterior. By running the simulation experiment, the aimis to show that the program can change the component in3D without exceeding boundary of the wall.

Other components of the building are to remain intact,while construction details of walls and floors are keptto the simplest level to reduce complexity and timeneeded for the simulation to run.

An overall simple geometry is used since the main focusof this experiment is to obtain an optimum result withrespect to daylight and cooling loads. It is also to showthe possibilities of generative optimization from thesimulation results.

A model from Revit has been created and exported intoIFC. The exported IFC is then analyzed to look at thequantity and type of components within the model from thewhole IFC schema. Each component is subsequentlyconverted into a class as described. IFCSpace is chosen asthe main component to extract the details to be converted

into EnergyPlus format which include the geometry of theallocated space in the model. As the process is extremelytedious, the possibility of total conversion can only beassumed once the data is being extracted from theIFCSpace component.

The simulation parameters are then assumed and asstated previously, window opening is chosen as the mainparameters to work on. Various set of window dimensionsare listed and created manually which the simulation arethen performed manually to each dimension. Total daylightluminance in the building is then compared to the coolingenergy needed for the building for each window dimensionand analyzed by tabulating all the results into a table.

Using pareto efficiency as the basis of optimization, afew results are obtained which give an adequate amount ofdaylight into the building yet does not consume too muchenergy. The results are then obtained from the Revitprogram manually and presented on a graph (Figure 7)

Figure 7Generative results after performance simulation

ConclusionAlthough the IFC file format is implemented in Revitarchitecture, there are still a lot of loopholes andproblems in it. One problem mentioned earlier is theincomplete model information exported into Revit. This isbecause some information is not extracted directly fromthe model into IFC. The important information which isneeded for simulation is the construction layer in awall. The class object, IFCMaterialLayer does not contain any

information regarding the material. They only consist ofdirection and thickness which is related to a wall.

Another problem is that in Revit, they do not have aplace to input human schedules and properties which arealso another important attribute needed for EnergyPlus torun accurately. In Revit, there is an option of creatinga new family class that allows you to add parameters intoit, which in turn can be placed into the specificlocation in the model to attach the required informationto the space. However, when extracted into IFC, althoughthe family class created is in it, it is not attached toany spatial zones. In other words, the relationshipbetween the family classes to the spatial zone is lostand the programmer would have to hard code the relationback.

The problems earlier can all be solved by hard codingthe information using java script but the main weaknessof using IFC in Revit is that it is a one way route out(Figure 8). Revit architecture can export the informationout into IFC for processing but when all the processingand simulation are done, it is impossible for IFC to beimported back into Revit. Thus, for this dissertation,the final presentation had to be made manually from theresult achieved from the simulation. Hence the stand inthis dissertation is to show that a generative simulationis possible using IFC schema and hoping that this willpush Revit architecture program into improving its linkwith IFC schema.

Figure 8Revit and its problems

For this paper, the prototyped software was exploredgenerally to envision the possibility of generativeoptimization. Limited parameters (due to the complexityin geometry algorithm) are used for user to decide theway to run the simulation. By using the paretooptimality, building design shall be improved to havelighting and thermal energy at the optimum level.

There are many possible developments which can andshould be done in order for performance simulation to bemore widely used. To increase the relationship ofgenerative optimization with architecture, more optionsor parameters should be included such that more solutionscan be provided architecturally. Other than optimizingthe envelope, it is would be useful if the architects canoptimize the spaces by designing. In this way, architectscould find a new way of spatial configuration that is notset using planning regulation but optimized to suit theclimate, a more important concern for the comfort of thebuilding users.

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