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A knowledge based CAAD system for passive solar architecture

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A knowledge based CAAD system for passive solar architecture
  A knowledge based CAAD system for passive solar architecture Abraham Yezioro * Faculty of Architecture and Town Planning, Technion-Israel Institute of Technology, Haifa 32000, Israel a r t i c l e i n f o  Article history: Received 23 September 2007Accepted 17 April 2008Available online 10 July 2008 Keywords: Knowledge based systemPassive solar architecturePre-conceptual design stageConceptual design stageComputer architectural aided designBio-climatic design strategies a b s t r a c t A computer-aided design tool for assisting the designer to set appropriate passive solar systems forheating and cooling is presented. The system is based on a knowledge base oriented design process(KBDP). The knowledge base stores design guidelines and procedural methods for determining thepassive systems that best suit the local climatic conditions. This tool is aimed to be used already atthe very early stages of the design process, the pre-conceptual and the conceptual, with the purposeof achieving a passive solar architecture from the energy point of view that will better fit localclimatic conditions. At the pre-conceptual design stage the system determined the bio-climaticstrategies and at the conceptual design stage the recommended passive systems are presentedaccording to previously selected design strategies. This paper focuses mainly on the later one i.e. theconceptual stage, in which the geometry, as well as the building orientation are determined. Thegeometrical considerations include the determination of the type and size of the passive systemsthat fit the requirements of both climatic conditions in winter and in summer at the given location.In addition, the design tool that was developed includes knowledge bases that contain examplesand descriptive explanations. The knowledge base may be retrieved automatically by the system orupon request. Thus the system can support the designer as an expert that provides advice whenneeded.   2008 Elsevier Ltd. All rights reserved. 1. Introduction The process of designing energy-conscious buildings can beviewed as a sequence of decisions made at different levels of abstraction, each successive level more detailed and specific thanthe former one [1]. These levels of abstraction correspond todiscrete design stages, which include [2–4]:1.  Briefing  : statement of user needs.2.  Pre-conceptual design : feasibility study and determination of detailed program requirements.3.  Conceptual design : exploring different schematic design alter-natives that agree with the programmatic requirements. Thisstage is concerned primarily with geometry and orientations,without considering material compositions.4.  Preliminary design : determining material compositions andbuilding details.5.  Detailed design : exploring different detailed design alterna-tives. This stage deals with the structure and material compo-sition considerations.6.  Design documentation : preparing building documents.The design process is characterized by being an ill definedproblem, which means that while searching for solutions, a betterunderstanding of the goals and constraints might occur. Therefore,the design process should be conceived as an iterative process (seeFig.1).Aniterativeprocessallowstoadvancesecurelyfromstagetostage, but at the same time enables the possibility of returning toprevious stages. As the design advances, it should acquire a greaterlevel of knowledge and details. However, the availability of therequired knowledge at the right time, and especially during theearly design stages, may reduce the necessity for too many itera-tions, or the need to go back to very early design stages, after anadvanced design stage has already been reached.Most of the available design tools do not comprise the overalldesign process. They rather consider only one of the abovementioned stages. Moreover, most design tools for the earlystages are manual, while the Computer-Aided Design (CAD) toolsand simulation engines, like DOE-2.2 [5], eQuest [6] and EnergyPlus [7] for example, are aimed to serve as evaluativetools at the advanced design stages, after the architect hasalready proposed a solution [8]. At these advanced design phasesonly the building detailing and materials can still be altered, butit may be difficult to take major measures for improving theenergy performance of the design, like changing the orientationand geometry of the building, that in most cases they hadalready been fixed. There are few exceptional CAD tools, though, *  Tel.:  þ 972 4 8294044; fax:  þ 972 4 8294617. E-mail address:  ayez@tx.technion.ac.il Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ – see front matter    2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.renene.2008.04.008 Renewable Energy 34 (2009) 769–779  that deal with bioclimatic and passive solar systems in the earlydesign stages. For example, Sunshades [9], PSD [10], Energy Scheming [11], Sustarc [12], BDA [13]. For the early design stages different design tools were proposedin order to assist the designer in choosing and implementing thepassive systems. The first type of design tools is manual methods.Mazria presented a book meant to be used as a manual design tool[14]. The book presents different bioclimatic passive solar heatingsystems that can be applied in the early design stages. It givesdesignguidelinesaboutgeneralrequiredsizeforthosesystems,butlacks the accurate treatment of local climatic conditions. Balcombsuggested design guidelines as simplified methods for determiningthe various passive solar heating systems [15]. This work does notdealwithpassivecooling.Loeffleretal.[16]suggestedamatrixthatrepresents the different passive systems for cooling and heating.The matrix shows the building elements required for each systemand their consistency for both passive cooling and passive heating.Their work is a manual design tool depicted by drawn schemes. Assuch, it is a fixed matrix that cannot be changed dynamically andautomatically in order to fit to the specific local climatic conditionsand the specific constraints of the project.ThesecondtypeofdesigntoolsfortheearlydesignstagesisCADsystems. Brown presented a CAD system for evaluating differentpassive systems for a proposed design [11,17], but no recommen-dations on how to improve the performance of the design solutionare shown. Shavivand Peleg [10] proposed a knowledgebased CADmodel for the conceptual design stage, where suggestions on howto improve the building performance are presented. Even thoughtheir model deals only with direct gain system, it considers veryaccurately the required size of this system for passive heating andcooling. Balcomb and Prowler presented a CAD tool (ENERGY-10)for designing low-energy buildings [18,19]. This tool enables the designer to evaluate at the same time both standard and improvedbuildings. This evaluation gives the designer energy consciousguidelines for improving heating, cooling and daylighting in thebuilding.In this work, a CAAD tool that is aimed to be used at the veryearly design stages; the pre-conceptual and the conceptual one ispresented. 2. The early design stages – the pre-conceptual andthe conceptual design stages Attheearlystagesofabio-climaticpassivesolarbuildingdesignthe following questions arise.1. What are the design strategies that best suit the climaticconditions of the project site, so that the building will requirenon-renewable energyas little as possible? The pre-conceptualdesign stage deals with this issue.2. What are the passive systems for both cooling and heating thatbest suit these strategies. Moreover, we need to know the rightsize for these systems in order to set the correct geometry,specially the massing and the orientation of the building. Theconceptual design stage deals with this issue.Nowadays, there is a wide range of knowledge related to bio-climatic and passive solar systems for both heating and coolingthat allows us to reach a passive solar architecture, from thepoint of view of energy conservation. The problem is that thedesigners don’t know how to reach the relevant information, orhow to implement it. As a result, the proposed design may lackappropriate climatic solutions. This paper presents a knowledgebased computer-aided design tool, PASYS (PAssive SYStems), thatis composed by two parts. The first part helps the designer inselecting the best-suited thermal comfort design strategies atthe pre-conceptual design stage. This part takes into account thelocal climatic conditions, as well as the building type to bedesigned. This part will be presented very briefly in Section 2.1,as it was presented with details in a former paper [20]. Theoutput of the first part is a number of possible combinations of climatic design strategies out of which the designer selects oneof them (see Fig. 2) which is the input for the second stage, thedetermination and the design of the passive systems for heatingand cooling. The second part, setting the systems type and sizefor cooling and heating, belongs to the Conceptual design stageand will be presented in this paper. This part contains a wideknowledge base that was developed in different studies and willbe presented in Sections 2.2 and 3. The system PASYS wasdeveloped as a continuation process, taking care of both parts,with the ability to go in cycles and return from the second partback to the first one, if no satisfactory solution is achieved.  2.1. The pre-conceptual design stage In the pre-conceptual design stage first adaptations betweenproject demands as is dictated by the program, specific constraints,specific conditions of the place and the available design strategiesare taken place. In this stage local climatic conditions are verifiedand checked against goals in order to establish design principlesthat best suit both place and project.From the climatic point of view the main goals for thisstage are.1. Toachieveathermalcomfortsolutionthatwillrequireminimaluseofnon-renewableenergy.Inotherwords,tolookforenergyconscious design solution on one hand, and to use, as far aspossible, passive solar and lowenergycooling strategies on theother, so that thermal comfort conditions are achieved.2. To reach goal 1 by using minimum thermal comfort designstrategies,which mean that a smallerdiversitypassive systemsfor heating and cooling will be required in the building. Goal 2will ensure that less different building elements should beadded to the building in order to achieve the required thermalcomfort, thus obtaining a simpler and more economicalsolution. Fig. 1.  The iterative design process.  A. Yezioro / Renewable Energy 34 (2009) 769–779 770  For this design stage PASYS presented a sensitive bio-climaticchart as a CAD tool for determining all possible combinations of passivecoolingandheatingstrategies.PASYSintegratedknowledgebaseandproceduralmethodsto allowachievingsolutionsthatbestfit the local climatic conditions and the type of building. Fig. 2shows a typical output of the pre-conceptual design stage thatincludesthebio-climaticchart(left),monthlyandseasonalanalysisshowing simple solutions (one strategy only) (right) and annualcomprehensive analysis showing composed solutions of two ormore climatic design strategies (top). As the designer picks one of the composed solutions in order to continue to the next stage, itbecomes the input for the conceptual design stage.  2.2. The conceptual design stage In the conceptual design stage schematic alternatives arechecked according to the program demands and the specific place.This stage relates mainly tothe definition of building geometryandorientation without referring in detail to materials [1].From the climatic point of view the main goal of this stage is todefine the necessary passive systems for heating and cooling in-cludingdeterminingtheirsizes,inordertoachievethermalcomfortconditionswithminimaluseofnon-renewableenergy.Climaticallyand economically we would like to achieve passive systems inwhich elements provide both passive cooling and heating yieldinga simpler solution. For example, the system of ‘‘direct gain’’ forpassiveheatinginwinterconsistsofsouthernwindowsandthermalmasstostoretheenergyfromdaytonight.Thesebuildingelementscan serve also as passive cooling system, which is ‘‘thermal masswithnightventilation’’.Therefore,ifinthepre-conceptualstagethetwostrategies:‘‘passiveheating’’and‘‘passivecoolingwiththermalmass and night ventilation’’ were found as the best climatic strat-egies for the project location, one should be recommended to usesuch passive systems as a solution. The model PASYS, developed inthis work, will recommend the solution of ‘‘direct gain’’ as the onethat is preferred, and will rate it as such (see for example Fig. 6 up-left). 3. The knowledge base required for theconceptual design stage Since we wish to have tools that support the design process, weare introducing the idea of the knowledge base design process(KBDP). The process relies on a per stage KB, meaning that insteadof a general KB for the whole process, there will be local KBs foreach stage. The advantage of this is that each KB can be morequickly accessed and easily manipulated. The KB supports any of the activities of each design stage, namely: Analysis, Synthesis andAssessment of the solution, at the level of each stage (see Fig. 3).TheKBisclassifiedaccordingto:Place,BuildingType,andAvailableTechnology. For each advanced design stage the level of detailing isincreasing and more specific information for these three categories Fig. 2.  PASYS – pre-conceptual design stage. Combinations of climatic design strategies in Tel Aviv (from Yezioro and Shaviv [20]).  A. Yezioro / Renewable Energy 34 (2009) 769–779  771  of KB is presented. The KBDP allows, as in the traditional designprocess to loop back to previous stages (as shown in Fig. 1).However, since the KBDP supports the designer decisions, theprobability of finding major faults in the design performance atlater stages will decrease. Hence, the continuity of the process ismaintained and fewer back loops will be required.The conceptual design stage is based on a wide knowledgebase published worldwide [i.e. Ref. 15] and special designguidelines developed for the Israeli climate and buildingtechnology [21]. In both cases the design guidelines weredeveloped by sensitivity studies using hourly simulation codes. Afull description of such design guidelines is presented by Shaviv[8]. The model PASYS does not propose new design guidelinesbut rather compiled and organized existing knowledge in orderto present the designer the relevant information at the right timewhen it is most needed. This paper presents the approach tohandle the various kinds of existing knowledge and the differentkind of KB that were developed. However, it does not include allthe knowledge in the area.The knowledge base includes the following topics (see Fig. 4).A. Heuristic rules representing design guidelines.B. Passive systems and their components.C. Knowledge base of existing passive systems – principles andexamples.  3.1. Heuristic rules representing design guidelines According to the goals of the conceptual design stage, theknowledge base includes information on topics related to thedefinition of the general form of the building, like orientation,proportions and the allowed area of outside walls. The knowledgebase should facilitate the retrieving, in an easy way, the relevantknowledge according to the place and the building type. Forexample, the recommendation of the required southern glazingarea and the area of the thermal mass needed to store the passivesolarenergy fromdayto night are notthe same in Jerusalem and inTel Aviv because of the different climatic conditions. In the samewayitwillbedifferentaccordingtothebuildinguseandoccupancypattern, for example, a residential building or a school. Even ina residential building a unit below the roof will require largersouthernwindow toheat the building inwinter than the same unitlocated in a middle floor. Moreover, the design guidelines fora standard insulated residential building may be different thanthose for an improved insulated one. Fig. 5 shows various designguidelines for both standard and improved insulated residentialbuildings in Tel Aviv [21,22]. Those heuristic rules include.1.  Orientation of the building  : related to the orientation of themain facade toward the south so that the passive solar systemlocated on it will still be effective. For instance, for a standardinsulated apartment on a top floor in Tel Aviv, the main facadeshould be oriented to the south sector, 40  east of south to 35  west of south.2.  Building proportion : determines the building’s energy lostthrough its envelope, but is also defined according to theclimate of Tel Aviv and the existing recommendations. Theproportion, for a residential building can be a free parameter.3.  Outside walls area : is defined by the number of external walls,where 1 W is 25% of floor area. As for example, 2 W meansa middle apartment, and 3 W means a corner apartment inattached residential building. This parameter determines thebuilding’s energy lost through its envelope.4.  Southern glazing area required for the different passive systems :this recommendation is a function of the area of the building(or the unit) and the passive system type to be implemented. Itassures that the amount of passive solar energy that thebuildingreceivesfitstherequirementsforthewinterandatthesame time doesn’t cause over heating in summer. As for ex-ample, the glazing area of a top corner apartment in Tel Avivshouldbe18%ofthefloorarea,whendirectgainsystemisused.5.  Thermal mass area : defined as a function of the requiredsouthernglazingarea,accordingtothepassive systemtypethat Fig. 3.  Basic scheme of the main activities in the conceptual design stage.  A. Yezioro / Renewable Energy 34 (2009) 769–779 772  was chosen as a solution. As for example, when the thermalmass is located only in a standard concrete Israeli floor withcementtiles,therelationofthesouthernglazingareatothefloorarea should be 9–1, in order to preserve a temperature swing of 3   C. When the thermal mass is distributed along floors andwalls (10 cm concrete wall with plaster on both sides), therelation should be about 16–1 in order to keep the same 3   C.6.  Shading coefficient  : in winter determines the percentage of southern glazing area thatshould be exposed tothe sun sothatenergy transmittance is effective. In summer it defines therequirements for reducing cooling.  3.2. Passive systems and their components Fig. 6 presents the matrix of the different passive systems forheating and cooling. In the horizontal direction the passive systemsthat suit passive heating strategies are presented and in the verticaldirection the passive systems that fit the cooling strategies arepresentedaswell.Sofar,thefollowingsystemsareincludedinPASYS.For passive heating:a. direct gain.b. vented trombe wall.c. greenhouse.and for passive cooling:1. natural ventilation divided in two sub-systems:cross ventilation.stack ventilation.2. high thermal mass and night ventilation.3. evaporative cooling.This knowledge base was built in such a way that allowsincluding other passive systems in future development. Fig. 5.  Design guidelines for residential apartment buildings in Tel Aviv. Left: standard insulated building; Right: improved insulated building. Up: recommended size for southernglazing and thermal mass for different passive systems (the scheme of the building present the different kind of floors; above columns, middle, and below the roof. In each floorthere are corner and inner appartments); Down: design guidelines for building orientation, wall area, building proportion and shading coefficient (from Shaviv and Capeluto [21]). Fig. 4.  The hierarchy of the knowledge base.  A. Yezioro / Renewable Energy 34 (2009) 769–779  773
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