COMMUNICATING PERFORMANCE ASSESSMENTS OF INTERMEDIATE BUILDING DESIGN STATES. Godfried Augenbroe* and Sten de Wit**

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1 COMMUNICATING PERFORMANCE ASSESSMENTS OF INTERMEDIATE BUILDING DESIGN STATES Godfred Augenbroe* and Sten de Wt** *Georga Insttute of Technology College of Archtecture, Doctoral Program Atlanta, Ga , USA Emal: **TU Delft, Faculty of Cvl Engneerng PO Box 5048, 2600 GA Delft, The Netherlands Emal: ABSTRACT Collaboratve buldng engneerng s a team effort n whch many elements have to be combned nto a unfed structure. The ams of the archtect, the engneer and all the other players have to merge nto a seamless desgn process. Ths paper deals wth the exchange of nformaton among the desgn team members, and ntroduces methods that enhance a partcular subset of the exchanged nformaton,.e. the nformaton related to performance of ntermedate desgns. A new technque s ntroduced to control the nvocaton of performance assessments as the desgn evolves, based on the avalablty and level of uncertanty of nput data. INTRODUCTION Buldng desgn s a cooperatve team effort, wth an nput from a multtude of actors, havng backgrounds n dfferent dscplnes. Recent research efforts center around the objectve to provde an ntegrated approach to the evolutonary desgn process, enablng the sharng of all relevant nformaton among the team members. Many of these efforts have tackled the problem of makng the buldng shape, t s structure, fabrc and physcal propertes avalable n such a way that sklled engneers can easly and rapdly deploy ther tools for an expert evaluaton of the desgn. An obvous necessty for effectve desgn support s the ablty to evaluate ntermedate desgn states rather than to merely evaluate the fnshed (detaled) desgn. Intermedate states are assocated wth ncomplete desgns, whch pose the harder problem as one s confronted wth mssng nformaton that prohbt the straghtforward use of detaled smulatons. A smple, every day example s the assessment of overheatng rsk when no decson has been made yet about constructon types of exteror and nteror walls, or on the type of solar shadng, or when no knowledge about the presence of other heat sources s avalable. Stll, the desgn team mght rase the queston of overheatng rsk because some decsons about the layout of the rooms and the aesthetc desgn of the facade have to be made at that stage of the desgn process. One way to approach the problem s to provde electronc desgn assstants whch, at the fngertps of the desgner, advse hm about the possble consequences of desgn choces. Desgn assstants usually are based on reasonng wth captured expert knowledge, structured accordng to analyzed prevous cases and extensve typologes of buldng desgns and predefned or parametrzed desgn aspects and decsons. Desgn assstants are deally suted to predct trends durng early decsons,.e. n the conceptual desgn phase. Another way to deal wth mssng nformaton s to use sound judgment to fll n mssng data and perform (detaled) smulatons wth the tools of the trade. In many cases both approaches are unsatsfactory. Whereas the frst approach suffers from the fact that the expert knowledge base s never complete (partcular detals of the current desgn are not taken nto account because the knowledge system has no stored knowledge about them), the second approach suffers from an abundance of (added) data and an artfcal ncrease n detal level of the desgn. The latter may lead to the unjustfed deployment of detaled smulatons and thus create overconfdence n the results. An thrd approach whch may be used as alternatve or complementary to the two above ones, s ntroduced below. The basc proposton of t s that any performance assessment s as good as the data

2 s t s based on. Gven the uncertantes n the nput data, the result of a smulaton and ts subsequent evaluaton wll not just produce a sngle value but a probablty dstrbuton of the evaluaton varable, and should be conveyed as such to the clent of the smulaton, usually the desgn team. Ths s not any dfferent n the case of detaled smulatons of complete desgns, when uncertantes stemmng from guessed materal propertes, assumed model parameters and the smulaton model as such, can not be avoded. Lack of data caused by ncomplete desgns just ntroduces addtonal uncertanty. The cornerstones of the approach that s advocated are the followng: a rch classfcaton of performance concepts, (along wth approprate ndcators and measures), assocated to ther pertanng buldng objects, on dfferent abstracton levels and for dfferent composton levels of a buldng a technque to control the schedulng of performance assessment tasks durng the desgn evoluton an uncertanty analyss and parameter screenng procedure to add constrants statng when t s approprate to nvoke a performance assessment because t s expected to add to the certanty of the assessment Wth these technques t s possble to determne whether t makes sense to assess a certan performance ndcator n the lght of certan mssng data. COLLABORATIVE DESIGN Informaton technology s a key enabler of team-style desgn approaches whch take full use of rapd exchange of nformaton, thus makng t possble for all players to work around the same nteractve core desgn. Based on recent developments n IT, and more specfcally n ntegraton technology, a new generaton of ntegrated desgn systems s under development. A recently concluded nternatonal research effort, COMBINE (Augenbroe, 1995) was desgned to develop systems wth the prme objectve to ncrease the level of ntegraton of desgn evaluaton actvtes. Concentratng on those players that deal wth the crucal decsons wth respect to energy and comfort performance of buldngs, a number of prototype systems were developed. A key delverable of the COMBINE project s the common buldng model, desgned to unfy dfferent representatons of the buldng,.e. actng as the central medum for sharng nformaton between actors. The model has been successfully used to exchange shape nformaton (e.g. generated by CAD systems) wth buldng performance evaluaton tools n the areas of energy, lghtng and comfort. However, the model s stll qute underdeveloped when t comes to the reverse exchange,.e. handng the real meanng and rch nformaton content of output results of these tools back to the other members of the desgn team. How to make the results of these calculaton tools avalable n a comprehensve and meanngful way s a challenge htherto more or less neglected by the research communty. Below, an approach s proposed, based on three basc mprovements: classfcaton and mproved assessments of performances and support for matchng performances wth requrements. These mprovements pertan to the representaton semantcs and metrcs of exchanged performance values. Another aspect s the accurateness and relablty of the performance values, n relaton to the avalablty and accuracy of data wth whch these values are calculated. The objectve s to use uncertanty analyses to determne the relablty of the exchanged performance data and moreover, determne when the avalablty of new data warrants the evaluaton or re-evaluaton of certan desgn performances. PERFORMANCE CLASSIFICATIONS IN BUILDING MODELS Electronc exchange of nformaton s based on a defnton of the semantcs (meanng) of the data we want to exchange and an agreement on the way we physcally transfer the data,.e. syntax. It s obvous that the frst aspect poses the bggest challenge. Semantcs need to be formalzed and hence expressed n (semantc) models n order to be unambguous and processable by computers. A model contans conceptual structures wth whch the relevant nformaton s captured n terms of enttes (basc concepts) and relatonshps between enttes. A varety of conceptual modelng languages can be used for that purpose. The models that form the bass of ths secton are developed n a formal modelng language. As full treatment of the models (Dekker, 1995), would be outsde the scope of ths paper, a more ntutve treatment s attempted, by whch the man purpose of the models s clarfed. They are a frst step towards ntegratng rch performance concepts nto any buldng model. In the ntal stages of the research the followng lmtatons were ntroduced: only a small subset of requrements and performances are consdered only requrements and performances assocated wth buldng zones are consdered, lmtng the approach to just that one decomposton level of the buldng only requrements assocated wth explct zoneusage crtera are consdered

3 Buldng Model Functonal Buldng Vew Physcal Buldng Vew Projected _zone Realsed_by fulflls Desgned _zone Fgure 1 Prncple of dual functonal and physcal vews supported by the Buldng Model The approach s based on a dstncton between functonal enttes, representng requred functons, thus mplyng requred characterstcs of (parts of) the desgn on the one hand, and physcal enttes representng chosen desgn solutons on the other. The basc prncple s depcted n Fgure 1. The expert consultant s called upon to supply performances evaluatons (related to energy use, mantanablty, fre resstance, etc.) of desgn solutons. It should be noted that the satsfacton of requred characterstcs by desgn solutons s what desgn s all about. Adequate buldng models that support ths assocaton on all dfferent decomposton levels, and through an evolutonary desgn path are the bggest challenge of future systems (Eastman, 1996). The work presented here s lmted to a much narrower scope,.e. the matchng of Desgned_zone performances wth requred Projected_zone characterstcs, and does not deal wth the much wder desgn evoluton scope. It should be noted however that the need for a full coverage of performance semantcs wll be mmnent n any future system. Note that all functonal enttes n Fgure 1 on the left have a realzed by relatonshp wth the physcal counterparts on the rght. The relatonshp can be used to nspect how and to what degree the requred characterstcs, stored wth the functonal entty, are ndeed met by assessed performances, stored wth the physcal entty. In order to convey the flavor, some hghlghts of the modelng approach for the functonal half are lsted below: Projected_zone can be a subtype of one or more classfed Zone_functons, dentfable wth certan zone_characterstcs (e.g. offce_zone, meetng_zone, transport_zone, fre_zone, etc.), each of whch carres a reference to documented rules and regulatons each Projected_zone s now assocated wth one or more Zone_Requrements; they are derved from the nherted zone characterstcs or derved from the desgn_bref the type of each zone requrement s defned accordng to a classfcaton of performance aspects (thermal comfort, ar_ndoor_qualty, energy, acoustc, lghtng) and quantfed by one or more nstances of performance_ representatons. Through these constructs, the buldng model contans the semantcs to allow a desgner to defne a Projected_zone (e.g. a corrdor), and fnd relevant regulatons (expressed as requrements pertanng to human traffc zones), derve requred characterstcs from them (e.g. vsblty, way fndng, etc.), classfy them (lghtng, amongst others), relate them to an approprate ndcator (e.g. for vsual performance), and lnk these to one or more performance_ representatons (e.g. average llumnance level on floor area by artfcal lghtng, or lowest llumnance level on any surface by daylghtng wth overcast sky ). The latter requres that the model contans a rch set of performance_representaton nstances, wth approprate measures (absolute or ordnal value) and unts. The performance_ representaton concept s ntroduced to categorze all types of performance expressons that need to be exchanged n the desgn process. Performance_ representaton s a data structure for the results of a performance evaluaton experment. It mnmally contans a measure, a value and a unt. Whle measure s a structure desgned to contan the relevant condtons that were appled n the performance evaluaton experment, value relates to

4 the outcome of ths experment. Snce some degree of uncertanty wll generally be nherent to the outcome, value should offer a set of approprate structures to communcate ths. Such a structure would contan, e.g. a mean value and a varance or a number of bns to whch probablty masses can be assgned. Fnally, unt s ntroduced to store the scale to whch the content of value relates. The approach to the other half of the model s fully analogous. A desgned_zone can be subjected to an evaluaton, as a result of whch t has a predcted state, whch can be evaluated to classfed performances (thermal comfort, ar_ndoor_qualty, energy, acoustc, lghtng, etc.), each assocated wth an ndcator whch s quantfable usng one or more performance_representatons (same as above). Ths enables the expert to conduct evaluatons on a desgned zone (e.g. corrdor), evaluate the smulated state nto certan aspects of performance (e.g. lghtng), choose a sutable ndcator (llumnance level) and supply a quantfed nformaton (e.g. the ones mentoned above). It s mportant to note that ths process nvolves nterpretaton and engneerng judgment by the expert consultant n terms of what and how he conveys relevant performance nformaton to other members of the desgn team. The constructs n the buldng model enable hm to express the nformaton n a pre-conceved, but comprehensve way. ASSESSMENT OF INTERMEDIATE DESIGN STATES Desgn s an evolutonary process. Many dfferent parts of the buldng are beng desgned separately, whereas many alternatves are n dfferent stages of refnement and detalng. Some partal desgn solutons are retaned, whereas others are dscarded or kept dormant to emerge at a later tme n the process. Rather than study the process tself, our approach ams to be generc to whatever type of desgn ratonale and desgn decson management s used. We study the role of the consultant and n partcular, how hs assessment roles vs à vs hs communcaton wth the desgn team can be enhanced. It s assumed that at any moment n the process there may be ssued an evaluaton request, drected at a consultant. If he s consulted at some ntermedate desgn stage, the frst decson that he has to make s whether or not the nformaton he has at hs dsposal enables to make that knd of assessment wth a reasonable level of certanty. As actor n an evolutonary desgn path, he mght have been consulted earler wth the same assessment request, so he wll want to check whether there s any new nformaton, relevant to the request, that warrants a new assessment. Multple representatons of performances along wth a probablstc analyss of the avalable nformaton are a key ngredent to allow hm to make these judgments. A task model constranng the sequence of assessment tasks, based on the avalablty of desgn data as nput, s the other basc ngredent. It wll be ntroduced n the next secton. Matchng performances wth requrements Desgn for performance s adopted as the leadng paradgm for the approach that s advocated here (Kalay, 1996), (Mahdav, 1996). Our focus s on the support of nformaton exchanges that enable the paradgm, n partcular wth respect to the quantfable techncal performance aspects that are determned to a large extent n the area of buldng technology where, tradtonally, the handshake between archtectural desgner and buldng engneer takes place. The ultmate am of ntegratng rcher performance concepts n buldng models s to enable the desgn team to nspect at any stage n the desgn the performance of the desgn as a whole. Desgners and experts wll want to check whch requrements are met and whch are not, nspect the ratng of the values of certan performance ndcators, or choose a part of the desgn and nspect the lst of all requrements and performance aspects that pertan to that buldng part. All ths should be adaptable to the context of the desgn task at hand, or the role and expert level of the desgn actor, who s accessng the nformaton. The latter s crucal n order to present only that nformaton whch s relevant to, and can be understood by the observer. It s not hard to see why these goals are dffcult to reach. It wll requre rch models of requrements and performances, fully ntegrated n a complex buldng model supportng multple abstractons and decomposton levels, and wth semantcally rch (context dependent) assocatons between them. In (Dekker, 1996), a prototype of a desgn system has been developed n order to show the potental use. The prototype s bult as a consultant s back end tool to the buldng model, dscussed n the prevous secton. After the consultant has chosen a partcular aspect that he s specalzed n (the aspects beng fxed by the classfcatons ntroduced before), he selects a (desgned) zone and the system provdes hm wth all relevant requrements,.e. projected functons whch the zone s to fulfll, and those performance aspects that match the expertse ( expert profle ) of the consultant. Each tem n the lst of requred performances s assocated wth specfc evaluaton tools whch, at the fngertps of the consultant, can be deployed (automatcally extractng data from the buldng model through dedcated nterfaces). Based on the results of the calculaton

5 runs, the expert wll supply nformaton n the matchng performance representatons and add them to the buldng desgn nstance n the database. The prme beneft of ths approach s that both the requrements as well as the evaluated performances are now accessble by any down-stream actor n the desgn process n a way that enables a straghtforward comparson, checkng for completeness, and nspecton of performance nformaton n the format and detal level that the observer has selected. As explaned above, probablty nformaton should be an essental part of the measure of a performance ndcator. Ths addtonal dmenson of the nformaton enables to control the nformaton content (n the true sense of the word) durng ncremental desgn and evaluaton. A MODEL OF DESIGN TASK CONTROL Ths secton explans the approach to a task schedulng model,.e. a formal, computer nterpretable representaton of the tasks, the actors that perform them and the constrants that control ther executon and sequencng. The model has been adopted from the COMBINE project It s based on the metaphor of a Project Wndow, whereas a Petrnet modelng technque, serves to derve the formal Project Wndow reference model. Both wll be ntroduced brefly below. Project Wndow The Project Wndow (PW) metaphor s ntroduced as a wndow on any sutable, lmted porton of the overall desgn process. Such a porton s usually lmted to a small tme perod of the project (typcally a project phase wth a well defned start and end state) and only a lmted numbers of actors (typcally lmted to a specfc sub-system n the buldng or dedcated to the exchange that takes place among actors n a partcular settng,.e. to reach a predefned decson pont). The PW approach has been proven to be an adequate nstrument to mplement ntegrated buldng desgn system prototypes drected at a partcular ndustral need. A number of PW models were generated wth nput from ndustry and IBDS prototypes were developed for them. A PW model descrbes actors, ther roles and tasks, the n and output data for each task and pre and post condtons that regulate the executon of the tasks. It should be noted that a PW model s no attempt at a generc process descrpton. Rather, t s the result of a workfloor approach to the project at hand. PW modelng tools should allow easy confguraton at the start of the project and on the fly reconfguraton. The executon of the PW model s done n nteracton wth the Project Manager, who s always n control over what task to execute next. The Comb-Net technque PW models are expressed usng a flavored Petr-net technque. Petr-nets are well suted to model control over the sequence of tasks. Several types of controls apply: condtons determnng when a specfc actor can perform a partcular operaton. (temporal logc control) condtons to ensure that the model remans n a consstent state whle the desgn progresses. (data ntegrty control) A PW model conssts of two dagrams The frst one captures all the Actors, ther Desgn_Roles, and the Desgn_Tools they can execute. The dagram descrbes all the communcatng enttes n the system and ther nputs and outputs. Cons. A actor desgn role Consultant Input EXPRESS schema Fgure 2. Combne PW Dagram Assess PI1 crroom.xps dlwnd.xps Assess PI2 crroomo.xps dlwndo.xpr Desgn Tool Functon (DTF) Perform. Evaluaton Tools Fgure 2 shows a example for one actor (Consultant A), havng the desgn_roles to assess two Performance Indcators, PI1 and PI2, both of whch are dentfed wthn the system as Desgn Tool Functons, assocated wth expert performance evaluaton tools. The dagram also shows the explct reference of each functon to a predefned subset of the buldng model. The latter aspect s not dealt wth here. The second dagram type, known as the "Combne_Petr" dagram, descrbes the order n whch these DTF's are allowed to execute n the system. These dagrams use the basc structures of Petr_net dagrams,.e. Places and Transtons, where Places represent (on the lowest granularty) desgn tool functons and Transtons represent all potentally allowed sequences from one Place to the other, subject to constrants. Output EXPRESS schema

6 Fgure 3: Sample ExEx screen. Fgure 3 shows a snapshot of a part of a Petr_net, n the runtme support tool that we wll brefly ntroduce below. Supervson and Exchange Executve In order to translate the Comb-Net control model nto an agent actvely controllng the buldng desgn system, an applcaton called the Exchange Executve (ExEx) was developed wthn the COMBINE project (Fgure 3) The project control based on the PW model was essentally developed to control scenaros n whch DTFs were allowed to access the central database. The ExEx s capable of readng n the PW model, create a bnary mage of the model n RAM and execute t. The ExEx tool determnes data dependences between all ndvdual DTF s and evaluates the state of the system based on the evaluaton of the pre and post condtons. After the executon of a DTF the ExEx wll show a lst of all possble next DTF s that the project manager ca choose from. It wll also show the lst of already executed DTFs whch mght have to be re-executed because part of ther nput data has changed. Ths paper adds an addtonal category of control optons to ths approach,.e. those relatng the avalable nformaton to the usefulness of performng a certan evaluaton. In that case, the project manager would usually be the local manager of the consultant s offce. TASK MODEL OF INTERMEDIATE ASSESSMENTS WITH UNCERTAINTY To apply the approach of the precedng secton to model and execute the control over f and when to perform a performance evaluaton, the followng premses should hold: desgn tasks and ther decompostons nto granular desgn tool functons (DTF) have been defned accordng to the rules explaned above for each DTF there s pror knowledge of the part of the buldng t needs as nput and the data t generates, e.g. n the case of a performance assessment tools the nput data and the output data (performance concepts related to the enttes n the nput) have been modeled pror and have been dentfed as a subset of the complete buldng model each DTF has a one to one relatonshp wth a performance concept and a tool or method to evaluate that partcular performance an explct two-way mappng has been defned to correlate the nput parameters to the nput/output models of the DTF Ths corresponds to the standard approach, whch always assumes that the nput data dependency of the DTF executon s purely a matter of whether that nput data s avalable or not. Ths prohbts the defaultng of mssng data and t also lacks the context of the performance request. In many cases t s permssble, gven the early stage of the desgn and the low requred accuracy of the evaluaton to

7 default mssng data (locally n the DTF applcaton) and stll be able to present meanngful nformaton to the desgn team. In many cases however, the lack of nformaton wll make an evaluaton useless and even msleadng n a gven desgn context. Extensons based on uncertanty analyss of DTF nput data For approprate DTFs n the PW, an uncertanty analyss s performed n order to formulate the constrants that determne whether the executon of the DTF (remember that a DTF has a one to one relatonshp wth a partcular performance concept and a specfc ndcator for t) makes sense, gven the avalablty of the nput data. Ths results n addtonal control over the executon of DTFs: the Petr-Net tself specfes the general order n whch a DTF may be nvoked (the standard control). It also specfes at what stage n the process more elaborate tools may be nvoked generatng new or regeneratng prevous performance assessments when nvoked, a DTF uses the desgn context (the poston and hstory of the token n the Petr-Net) and pror uncertanty analyss to determne whether t s permssble to default mssng data, usng some nternal default values In the case of desgn loops, when the DTF s repeatedly nvoked n an ncremental evaluaton sequence, pror uncertanty analyss s used to determne whether the change n nput data warrants a new evaluaton (the change n the nput parameters mght be such that no sgnfcant decrease n the uncertanty of the result can be expected). The next secton wll show how the nformaton for the uncertanty related control of the executon of performance evaluatons can be generated UNCERTAINTY ANALYSIS OF MISSING DATA In present day practce, the DTF s are executed determnstcally,.e. nputs and parameters of the underlyng model are treated as known values (Fgure 4) However, the values of these parameters and nputs wll often be uncertan. Examples of sources of uncertanty are: 1) buldngs are not constructed exactly to specfcatons. 2) the buldng desgn specfcatons are nsuffcently detaled 3) the model does not fully capture the complex (physcal) processes t clams to descrbe. The actors n the desgn process need quanttatve nformaton about these uncertantes n order to control the relablty of ther desgn decsons. One way to acheve ths, s to make uncertanty analyss (Fgure 5) an ntegral part of the performance evaluatons (de Wt, 1997) and enrch the nformaton structures n order to allow the uncertanty assessments to be shared n the desgn process. If we want to ntegrate a full uncertanty analyss nto the DTF, a jont probablty dstrbuton over the nput parameters would be requred as nput for the DTF, and each executon of the DTF would mply a cyclc refnement of ths pdf. Snce rgorous changes DTF pont estmate of x (smulaton) model pont estmate of y desgn tasks Fgure 4 Tradtonal uncertanty analyss, no update of nformaton: refne jont pdf over x w.r.t {x } mportant estmate of jont pdf over x parameter screenng: assess {x } mportant propagate pdf of x through model pdf over y Fgure 5 The uncertanty analyss cycle s repeated untl the resultng pdf (probablty densty functon) over y no longer changes sgnfcantly.

8 of the parameter vector may be expected n each desgn cycle, these refnements would often prove rrelevant. Moreover, the estmates for the uncertanty n the parameter vector wll be of such a crude nature, that nstead of a full probablty dstrbuton to quantfy the parameter uncertanty, ther covarance matrx suffces. Ths means that the nput requred by a DTF wll consst of the parameter data: (µ x, C x ) where µ x s the parameter mean vector and C x s the parameter covarance matrx. Consequently, the output of the DTF wll consst of the data (µ y, C y ). Here, we make the addtonal assumpton that the model behaves suffcently smooth to use a smplfed model for the uncertanty assessment,.e. a lnearzaton y of the model y around the parameter mean vector µ 0 x. y 0 yx () = y0 + ( x x, ) x µ (1) Wt ths assumpton, the executon of the DTF can be very effcent: The frst tme the DTF s executed, the lnear model must be bult,.e. the value of y 0 and the dfferental senstvtes are assessed. Each call of n the desgn cycle, ncludng the frst one, requres as nput data the parameter mean vector µ x and the parameter covarance matrx C x at that stage. On the bass of the covarance matrx, the DTF calculates the varance V y of the lnearzed model y : ( { 0) } y Vy = E y y = x 2 j y x C, j xj (2) as an estmate for the actual model varance V y. To check whether y 0 s stll a vald estmate for the mean model output y, gven the new parameter values, the devaton of the mean value of y from y 0 s estmated by: y 0 = E{ y} y0 = ( µ x, µ x, ) (3) x If << V y we wll assume that the change n the mean value of y wth respect to y 0 due to the new parameter values s nsgnfcant. Now, y 0 s no longer exactly equal to the mean of y but an acceptable approxmaton. If, however, V y, y 0 can no longer serve as an approxmaton for µ y. In that case, a new lnearzed model has to be bult around the current parameter mean vector and the varance estmate has to be recalculated. At ths stage, the DTF can decde on the bass of the varance estmate for y whether the calculaton output should be released. In other words, f the varance has an unacceptable magntude, the DTF can decde that storage of the results n the central database s unacceptable. If release of the output s deemed to be acceptable, the DTF outputs (y 0, V y ). CONCLUSIONS A novel approach has been ntroduced to deal wth ncremental performance analyss strateges n collaboratve buldng desgn teams. Based on rgorous defntons of performance assessments and ther metrcs wth ncluded probablty nformaton, the approach enables to control whch assessments become avalable as the desgn nformaton content grows. It also ndcates f and when a pror assessment s nvaldated by new nformaton. Future work s targeted at establshng the reverse lnks,.e. to determne whch performance ndcators can be evaluated wthn a predefned level of uncertanty for a gven ncomplete desgn. Much effort has to be put nto the mappng of data between evaluaton applcatons, keepng track of all correspondences of changed desgn nformaton and the local parameters n the applcatons. The Combne approach s too crude n most cases. Other approaches (Eastman, 1996) wll be used n future extensons. The technque s presently beng tested on overheatng rsk assessments n dfferent stages as the desgn evolves. REFERENCES Augenbroe, Godfred. COMBINE Fnal report. CEC- DGXII report (1995) Dekker, Sl. A Desktop COMBINE nterface for the buldng physcs consultant (n Dutch). MSc Thess Report, TU Delft, Eastman, C.M. Managng Integrty n Desgn Informaton Flows, Computer Aded Desgn, May 1996, 28:6/7, pp Kalay, Yehuda E., Performance-based Desgn, Applcaton of the Performance Concept n Buldng, Tel Avv, Dec. 1996, pp Mahdav, Ardeshr, Computatonal Support for Performance Based Reasonng n Buldng Desgn, Applcaton of the Performance Concept n Buldng, Tel Avv, Dec. 1996, pp Wt, Sten de, Influence of modelng uncertantes on the Smulaton of Buldng Thermal Comfort Performance, These Proceedngs.