HANDLING DAYLIGHT IN THE EARLY DESIGN STAGE

Bernard Paule, Jean-Louis ScartezziniSolar Energy Laboratory, Swiss Federal Institute of Technology, LESO-PB / EPFL, CH-1015 Lausanne,

Tel: + 41 (0)21 693 55 54, Fax: + 41 (0)21 693 27 22, E-mail: bernard.paule@epfl.ch

Margaret Reynolds, Nick BakerThe Martin Center for Architecture and Urban Studies, 6 Chaucer Road, CB2 2EB Cambridge,

Tel: +44 1223 331 700, Fax: +44 1223 331 701, Email: nvb11@pop.cus.cam.ac.uk

Abstract – Taking daylight into account in architecture constitutes a complex problem. The number ofrelevant parameters is so high that it makes forecasting delicate and uncertain. Experience shows that thesubject needs to be approached when the first draft of a building is made. However, the tools available toarchitects are most often little adapted to this project phase and often quite ineffective. If it is reasonableto think that very complex problems should be left to specialists to solve, it is nevertheless important thatcertain decisions with major consequences for the architectural design can be taken by the architecthimself.The experience of LesoDIAL shows that when combining an intuitive approach (interface) withsimplified algorithms (calculation) and fuzzy logic rules (optimisation), it is possible to propose a reallyefficient and helpful tool for designers.This paper appraises the adequacy of this tool for both professional and educational purposes, after 2years of diffusion.- Some results of the validation procedure initiated within the IEA SHC TASK 21 / ECBCS ANNEX 29

are presented.- An evaluation of its application in real situations by several groups of users is presented (analysis based

on questionnaire evaluation)- New facilities of the tool are presented :

Possibility to compare one’s design with similar reference cases in a database,Design of atrium buildings.

- Future developments initiated within the European Project « DIAL-Europe » are briefly exposed.

1. INTRODUCTION

Funded by the Swiss Federal Office for Energy and theSwiss Federal Institute of Technology of Lausanne, theconception of LesoDIAL started in 1995 (Paule et al.1995). The third version of this software is now availablein French and English.The aim of this tool is to allow architects and designers toquickly have an overview of the implications of theirdecisions regarding the use of daylight.

The basic idea of this tool is well illustrated by Richens:"… an easy system is one that can be quickly learnt…Once learnt, it should be possible to use efficiently,without making a great number of mistakes, without agreat effort of concentration, and without constantreference to manuals. Finally, skill once acquired shouldbe readily retained, so that the software is easy to comeback to after an interval… Simplicity has to be designedinto a system and pervade its every aspects." (PaulRichens, cited in Robinson, 1996).

The program consists of the four following modules plusa “Lexicon":- Function Module: Selection of the main activity(-ies)

that will take place in the room.- Description Module: Description of both photometry

and geometry of the room through the handling ofgraphic and linguistic items. Thanks to fuzzy-logicalgorithms, one can describe parameters even if they arenot precisely known. The last developments of the toolmake it possible to take atrium geometry into account.

- Evaluation Module: Calculation of both daylightingautonomy and daylight factor on the work plane (usinga «split-flux» method). Diagnosis for the optimizationof the design (using fuzzy-logic rules).

- Comparison Module: Access to a case-study databasefor the comparison of the user’s design with existingrooms.

- Lexicon: about 100 terms of the lighting vocabulary arepresented in a richly illustrated way.

In this paper emphasis is placed on the evaluation of thisprogram by users.

2. VALIDATION

2.1 Room calculationsAs a part of IEA SHC TASK 21 / ECBCS ANNEX 29,Subtask C outcomes, a validation procedure has beendefined for the comparison of results from differentcomputer tools with scale model measurements(Fontoynont et al, 1999). Fig. 1, 2a & 2b show two of theexamples which were used in this validation work, andsome of the results. We can see that the level of accuracyof LesoDIAL is within the range of other software andcan be considered as very satisfactory.

Black wallsCell EPFL scale Superlite Genelux Adeline LesoDIALA 7.06 7.7 7.69 6.47 7.58B 1.04 1.04 0.92 0.98 1.10C 0.45 0.42 0.49 0.43 0.43

White walsCell EPFL scale Superlite Genelux Adeline LesoDIALA 10.16 9.69 8.93 8.34 10.22B 2.91 2.2 1.56 1.92 3.34C 2.07 1.41 0.94 1.19 2.15

Figure 1: Comparison of some results based on the LESOscale model data (black and white walls).

Figure 2a: Description of the BRE scale model used inthe IEA Validation.

Black wallsLevel BRE scale Superlite Genelux LesoDIAL

0 10.7 10 9.91 10.11 13.7 13.3 12.95 13.42 18.9 18.3 17.78 18.43 26.7 26.5 25.97 26.64 40.2 40.4 38.17 40.65 61.9 63.1 61.36 63.86 89.9 90.8 90.93 92.2

Light Grey wallsLevel BRE scale Superlite Genelux LesoDIAL

0 19.1 15.3 15.38 171 23.9 20 19.73 212 30.7 26.8 25.56 26.93 39.9 36.6 37.77 36.24 53.3 51.3 49.81 51.45 71.8 72.5 70.05 76.26 94.4 64.5 - 100

Figure 2b: Comparison of some results based on the BREscale model data (black and light grey walls).

2.2 Atrium configurationsThe tool was recently extended to take atrium buildingsinto consideration. A "calibration" procedure wasinitiated to compare LesoDIAL results with Superlitecalculations (see § 4.2).

3. EVALUATION

3.1 Teaching environmentAlong the design / development of the tool, several testswere conducted in order to check its simplicity, rapidity,familiarity and intelligibility (Paule, 1999).About 100 students of the EPFL department ofarchitecture were asked to use the different versions ofthe software and to answer a questionnaire.

The evaluation procedure was as follows:- A "Before" questionnaire testing the students'

understanding of daylighting.- An exercise of a room description to input and evaluate.- An "After" questionnaire with the same questions as

above.- A questionnaire evaluating the tool.

This procedure put emphasis on the following points:

a) The tool requires no training or user manual. Thestudents were able to complete the exercises and toanswer the questionnaires in the 2 hours allotted andindicated no trouble understanding its use or results.

b) The students acquired knowledge about daylightingby using LesoDIAL. Comparison between Before andAfter questionnaires shows that the use of the tool leadsto a regression of wrong answers and a progression ofcorrect answers for questions on daylighting (see Fig. 3).

c) The users agreed that the choice of a graphic,linguistic or numerical description mode was helpful.

0

WRONG NA

1

Num

ber

of A

nsw

ers

BEFORE

Range of recommanded g-value for shading devices

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

RIGHT WRONG NA

AFTER

RIGHT

Figure 3: Comparison of Right/Wrong answers beforeand after the use of LesoDIAL (NA = No Answer).

3.2 Professional useAn evaluation session with British architects was carriedout by Margaret Reynolds (Reynolds, 2000).

Representatives from 13 architecture firms in theCambridge area participated in the study. The size of firmranged from sole practitioners (4) to firms of 2 to 19architects (6) to large firms of over 20 architects (3). Theaverage number of years of practice for the individualsundertaking the trials was 18.9 (min 2 years, max 30years).The session was divided into three parts:- Background information questionnaire- Evaluation exercise- Architects' evaluation questionnaire

Having learned to get information, manipulate parametersof a room and navigate around the LesoDIAL program,architects were asked to rate the features of the programfrom 1 to 5 (poor to good). Most highly or badly ratedfeatures are exposed below in the next two tables.

Topic Rate(/5)

The quality and type of illustration (in Lexicon)reinforce the content of the information

4.42

The choice of entering a precise (numerical) value oruse linguistic and/or graphic description is helpful

4.38

Computer software is better than a reference bookfor this subject matter

4.38

Shading devices 4.23Daylight factors (graphic and numerical results) 4.23Diagnosis 4.15(Providing) requirements by building type 4.08Frame area openings 4.00

Table 1: Most highly rated features (on average).

Topic Rate (/5)Getting started using the tool presented noparticular problems

1.92

Overheating 2.15Roof geometry 2.57Glare 2.77If you need information you naturally tend tocheck the "Lexicon" function

2.92

Facade numbering 3.08Table 2: Most badly rated features (on average).

3.3 LesoDIAL objectives reviewedMoving from a teaching environment into the pressureworld of practice, necessitated re-considering the initialobjectives of the tool.

- Feasibility stage : Architects would appear to seeLesoDIAL as more useful at "Detail / Tender stage"than at "Feasibility stage".

- Simplicity of use: The stipulation "no training, no userguides" is optimistic.

- Rapidity: LesoDIAL could incorporate more complexoperations and databases without detriment to itsusefulness.

- Familiarity : Results of evaluation confirm the successof the initial goal of accommodating the tool to thearchitect rather than the reverse.

- Intelligibility : LesoDIAL does offer simple advice,plain language and practical results, this is surely areason for the positive reaction of the architectsconsulted. If anything the call is for even greaterpracticality, in the form of specification clauses andproduct information immediately useable in contractdocuments.

- Based on Standard Requirements: Architects confirmedthe need for this.

- Optimisation facility: Architects responded verypositively to LesoDIAL's capability for interactiveimprovement of a design.

- Comparison: Although comparative case studies werenot part of the evaluation, architects' reactions to theidea of comparative buildings confirm the interest ofincluding a case-study database calibrated to permit there-utilisation of "generic" solutions.

To conclude this evaluation procedure, one can say thatLesoDIAL was rated highly by a sample of practisingarchitects : the average score of 3.72 out of a possible 5represents 74.4% approval. More than half of trialparticipants commented spontaneously that they coulduse it now on current jobs.

Some aspects need to be adapted to match architecturalpractices more precisely, most of them are exposed in thenext paragraphs.

4. NEW FACILITIES

4.1 Case-study databaseIt has been shown (Guéna 1992) that architectural designprocess is based on the re-use of generic solutions,coming either from their own experience or from theanalysis and interpreting of existing architecturalreferences. From a general point of view, the possibilityto compare different solutions is a very efficient way tohighlight the possible positive or weak points of a project.

The major evolution from version 1.0 to 2.0 consisted inadding a case-study database including 47 real rooms and40 simulated rooms. The idea was to allow designers tocompare their design with documented reference cases.The concept of "fuzzy outranking relation" (Slowinski1994, 1997), which is adapted to express the resemblanceof several objects, has been used to match, in thedatabase, the case(s) that present some similarities withthe one described by the user.When considering one parameter separately, the principleis to determine the difference between the user's roomand each of the case-studies. We use fuzzy relationshipslike:

"The smaller the difference the higher the resemblance"

Figure 4 schematically illustrates this kind of function,using the analogy of a light cone "revealing" objects.

Figure 4: Notion of "observation cone" used tocharacterise the resemblance of the case-studies in thedatabase.

Each case-study is looked at, parameter by parameter,and depending on its characteristics, is considered as"concordant" or "discordant" with the user's room(reference). Partial concordances and discordances arethen aggregated; so the global resemblance of each case-study is expressed with a credibility level (Paule 1999).

Comparison is made of the following points:- Typology (facade aperture, double side lighting, roof

lighting, …)- Opening Index- Geometry (proportions of the room)- Photometry

Figure 5 shows an example of partial and globalcredibility levels for 20 of the case studies. In thisexample, only two buildings have a global resemblancewith the one described by the user. The level ofcredibility indicates that Case N° 8 is more similar(Credibility = 0.8) than case N° 9.If no object of the database is "similar" with respect to allthe points (global credibility level < 0), the programoutlines the objects which present a partial resemblance(partial credibility level > 0).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

0.2

0.4

0.6

0.8

1.0

GLOBAL CREDIBILITY

Typology Credibility

Opening Index Credibility

Geometry Credibility

Photometry Credibility

Figure 5: Example of global and partial credibility of aset of objects compared to the user's room.

Figure 6 shows the way parameters are compared anddisplayed, while Figure 7 shows an example of the case-studies stored in the database.

Figure 6: Display of the comparison between the user'sroom parameters (photometry) and one of the case-studies in the database.

Figure 7: Inside view of one of the case-studies,displaying some of the main chacacteristics of amonitored room (geometry and photomoetry) (LesoDIALscreen shot).

4.2 Atrium buildingsAtria are very common in some countries (eg inScandinavia), specially in office buildings. As theprediction of daylight availability is not obvious in thiscase, we were asked by several users to adapt LesoDIALso that atria configurations could be taken into account.

4.2.1 DescriptionThe input interface is based on the same philosophy asthat of former versions of LesoDIAL. For each facade,the user is asked to select either an open outsideenvironment or an atrium. The atrium geometry isselected by typing numbers or dragging edges to theappropriate dimensions. Then photometry parameters aredescribed by selecting linguistic items (see Fig. 8a & 8b).

The following parameters are taken into consideration todescribe the atrium:- Atrium Typology,- Atrium Height, Width & Depth,- Position of the room in the atrium (Face,x,z).- Reflection factor of atrium opaque walls- Percentage of glazed area of atrium walls- Glazing type- Frames

Figure 8a: Types of atria considered in LesoDIAL.

Figure 8b: Some elements of the graphic interface used inthe atrium description.

4.2.2 Daylight factor calculationTo calculate the external reflected component of thedaylight factor, LesoDIAL assumes that the luminance ofthe obstructed portion of the sky is proportional to theCIE overcast sky luminance weighted by the reflectionfactor of the obstruction (BRE 1996).

Fig. 9 shows a comparison of LesoDIAL and Superlitefor some specific configurations. We can see that for lowvalues (DF < 5 %) the results are quite similar (error <10%). On the other hand, LesoDIAL is quite optimisticfor points located close to the opening. A detailedanalysis shows that mean values are very close. Thoughmaximum values are systematically overestimated inLesoDIAL, when translated into daylighting autonomy(time during which artificial lighting can be switchedoff), results are really comparable.

Daylight Factor Values (%)

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14LesoDIAL

Sup

erlit

e

Figure 9: Comparison of daylight factor values betweenLesoDIAL and Superlite for various positions of a roomin an atrium.

Anyway, if we keep in mind that this tool is mainlydedicated to preliminary studies, in the early stages of thedesign process, precision is not a goal in itself. It is moreimportant to have quick information about a tendencyrather than absolute precision about an object whosedesign is still in process.

5. FUTURE DEVELOPMENTS: "DIAL-Europe"project.

A European project, "DIAL-Europe", that started 1stApril 2000, intends to make LesoDIAL more Europeanand to add new facilities. The goal is still to assist theearly design of windows in buildings and lead to betterenergy and environmental performance. Work will focuson the following points:- Daylighting:

Extension of the existing LesoDIAL for Europeanclimates (including the usefuless of light from sunny

skies), incoporation of advanced daylighing systemsand visual comfort criteria.

- Artificial lighting:Implementation of simplified algorithms for theevaluation of artificial lighting strategies, controlsystems and integration with daylighting.

- Heating / Cooling:Embedding an integrated energy model and overheatingpredictor model.

- Case-studies database:Extension of the existing database to include Europe-wide examples and production of simulated cases(using Adeline software) to allow architects acomparioson of their design with a wide range ofexamples.

The participants in this project, selected for theirexpertise in these different fields, are :- The Martin Centre for Architecture and Urban Studies,

University of Cambridge (coordinator).- Ecole Polytechnique Fédérale de Lausanne, LESO-PB/

ITB EPFL, Switzerland,- Fraunhofer Institute für Bauphysik (FhG-IBP),

Stutgartt, Gernany.- Netherland Organization for Applied Scientific

Research (TNO-B)- ESTIA sàrl, Lausanne, Switzerland.- Intituto de Engenharia Mecânica e Gestão Industrial

(INEGI) Sao Mamede de Infesta, Portugal.

6. CONCLUSIONS

When setting up the LesoDIAL project, one pitfall to beavoided absolutely was to try to build a tool whose finalresult is to produce "the optimal solution". Such a systemwould have been not only ineffective, because of itsstrongly reducivist nature, but it would have been,probably, radically rejected by architects because itwould implicitly deny the intrinsic role of creativity indesign.

Experience has shown that when trying to meet the wayarchitects design (working on concrete solutions,simultaneously using figures, graphics and linguisticitems in the description, proposing optimization threwdiagnosis function, etc.) LesoDIAL was highly rated byusers.

Thus the need of really simple, easy and quick toolsaiming to help architects in the field of daylighting isconfirmed. It seems that the evolution of standards andrequirements might further the dissemination of suchtools. In fact, more and more building owners ask foroptimised daylighting.

All this encourages us to continue work on LesoDIAL,overcome its limitations and extend its functions.

REFERENCES

Bodart M. (1997) LesoDIAL: Validation report ondaylight factor calculation. Working document of the IEA-SHC Task 21 ECBCS Annex 29, Daylight in Buildings,Subtask C4, Simple design tools. Université Catholiquede Louvain La Neuve, Belgium.

BRE - British Research Establishment (1996) Estimatingdaylight in buildings. Part 1 & 2, Digest 309 310,Building Research Station, Garston, Watford,Hertfordshire WD2 7JR, England

Guéna F. (1992) Réutilisation de solutions génériquespour résoudre des problèmes de conception. Thèse dedoctorat, Université Paris VI LAFORIA, Institut BlaisePascal, France.

Fontoynont M. and Lafforgue P. and Mittanchey R. andAizlewood M. and Butt J. and Carrol W. and HitchcockR. and Erhorn H. and De Boer J. and Dirksmoeller M.and Michel L. and Paule B. and Scartezzini J.-L. andBodart M. and Roy G. (1999) Validation of daylightingsimulation programmes. a report of IEA-SHC Task 21ECBCS Annex 29, DGCB-URA CNRS 1652, ENTPE,France.

Paule B. and Compagnon R. and Scartezzini J.-L. (1995)Toward a new daylighting design computer tool

Proceedings of the Right Light 3 Conference, Newcastle,England.

Paule B. and Scartezzini J.-L. (1998) Leso-DIALDaylighting Design software. In Proceedings ofDaylighting’98 conference, Ottawa.

Paule B. (1999) Application de la logique floue à l'aide àla décision en éclairage naturel. Thèse N° 1916, EcolePolytechnique Fédérale de Lausanne, Suisse.

Reynolds M. (2000) Designing for Daylight and EnergyPerformance: A 'design support' tool evaluated.Environmental Design Dissertation. M Phil inEnvironmental Design in Architecture, King's CollegeCambridge.

Robinson D. (1996) Energy model usage in buildingdesign: A qualitative assesment. In Proc. CIBSE A:Building Serv. Eng. Res. Technol. 17(2) pp 89-95.

Slowinski R. (1994) Rough Set processing of FuzzyInformation, proceedings of the RDSF'94 Conference,San Jose, California.

Slowinski R. (1997) La théorie des ensemblesapproximatifs et ses applications dans l'aide à la décision.Institut d'Informatique, Université de Technologie dePoznan, Poznan, Poland.