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SOLAR RADIATION IN EARLY BUILDING DESIGN STAGES Introducing the "Solar Workshop" as Web-Accessible Design Support for Architects Margit Rudy Technical University of Vienna bau><studio Urban Loritz Platz 7/22 A-1070 Vienna, Austria (+43-1) 522 0372 rudy@baustudio.com ABSTRACT. Building science is playing an ever-increasing role in the integration of passive energy use techniques in the architectural design process. The methods for communicating the information that the science can provide to architects, however, are still very underdeveloped and generally bound by an academic context. Thus for making key decisions, especially early in the design process, most architects are left with the choice of either delegating all technical responsibility to energy consulting experts, or resorting to overly simplified, but easily accessible guidelines. Since customized (i.e. genuinely site-specific) information is very expensive to come by, the latter is usually the case. However, when attempting to assess the impact of competing options, such commonly accepted rules of thumb are often too generalized to answer the specific design questions at hand in a reliable manner. The immanent effect of this insecurity in early decision-making is that the potential of the projected building in terms of passive energy use will not be fully realized. The concept of an Internet-based solar workshop, presented in the following, aims at bridging the information gap between building science and architecture more effectively by means of globally applicable computational tools that are directly accessible to the building designers themselves. 1.

THE APPLICATION METHOD OF SOLAR PROFILING

From the architect's point of view, solar building physics is immediately relevant to two primary aspects of design considerations: the optimization of thermal comfort and the economy of means. Beyond this, solar design issues also directly influence lighting options and, ultimately, psychological and aesthetic qualities of the architecture itself. The relative importance of these design objectives varies according to the priorities specific to each project as well as to the designers and clients involved. Generally, however, it can be said that technical aspects that demand a high degree of pre-specification for assessment are only of peripheral interest to the architect at early design stages. Satisfying such information needs calls for a system of design support tools that targets a number of goals in equal measure [1]: Â&#x192; provides a means for generating custom information specific to the site, situation and overall project objectives. Â&#x192; allows the architect to "gain a feel" for the physical parameters involved and how the design is developing in these terms.


ƒ requires only input that is horizontally consistent (in extent and level of detail) with the building design in progress. ƒ yields answers to design questions as they arise in the decision-making process. ƒ emphasizes comparative interpretation (qualities) – rather than absolute numeric results (quantities). ƒ complements and enhances conventional methods of describing a building design. To meet these goals, solar radiation information should ideally be modeled with the same level of detail and validity as the geometric information that architects are accustomed to working with. A tight coupling of solar radiation data and design geometry from the start of the design process serves to enhance intuitive understanding of solar influences, as well as to establish comparable design profiles for competing concepts. The entire extent of the building design process can be broken down into four main phases in order to roughly categorize the types of design decisions encountered [2]: I. Conceptual phase, which covers programming, site/situation analysis, and an assessment of basic options for building shape and placement. II. Schematic phase, which entails the commitment to a basic design strategy and certain key functional, structural, and architectural aspects of a preliminary design concept. III. Developmental phase, in which the design concept evolves in increasing depth and detail, ideally in a manner which progressively verifies the chosen strategy. IV. Final phase, which includes detailing and technical fine-tuning of building components as well as construction documentation. The specific content of each phase is, of course, dependent on the concrete project, and especially on whether the design is for new or retrofit construction. Nonetheless, the four described stages do provide a theoretical framework for relating thermal consideration in general – and solar parameters in particular – to more or less equivalent levels of design information (fig. 1). The data required for the solar and climatic aspects of an overall thermal simulation model [3] conveniently coincide with information that is available at the earliest stages of the building design process, i.e. during the conceptual phase. The objective of the solar profiling method is to utilize this information to reveal as much as possible about where the design stands in solar terms – without making any premature assumptions as to the thermal properties of the building envelope [4]. As the design model is developed through subsequent levels, it should yield further and increasingly specific profiles, and ultimately serve as the basis for more involved thermal performance assessment [5]. In order to facilitate the understanding of solar dimensions in a schematic yet consistent fashion, the profiling method on the whole works with physical dimensions of energy and geometry (e.g., W/m2). It is aimed at characterizing a building's solar potential from its inception and, therefore, the initial focus is not so much on computing absolute numeric quantities as it is on generating qualitatively comparable visualizations and renderings (fig. 2) [4, 6].


Figure 1:

Correlation of typical building design phases with solar/climate profile levels.

Figure 2:

Tracking surface for summer and winter dates; solar flux on the site/building model at noon on the summer date.


2.

IMPLEMENTATION OF THE SOLAR TOOLBOX

The solar toolbox application is structured closely along the lines of the solar profiling method described in the previous section, whereby each "tool" is a program module for processing the set of input parameters that is needed for a further level of output options. The individual output options are systematized to support the targeted manner of profiles for early building design guidance, that is, site analysis and schematic building design development. Consequently, the principal solar toolbox prototype is conceived to contain the following sequence of modules [4]: a) solar geometry – for calculating diurnal solar positions and rendering tracking geometry based on geographic site specifications. b) solar energy potential – for calculating the site-specific solar flux envelope based on solar positions, atmosphere and terrain parameters, as well as distant-field obstructions. c) solar access – for calculating the diurnal specific flux and angles of incidence on surfaces of user-defined orientations (azimuth/tilt). d) site/building model – for calculating and rendering the shading patterns and resultant flux on the full incident surface geometry of a building design (accounting for middle-field obstructions). e) building details – for calculating the resultant flux on detailed regions of the building model's incident surfaces, i.e. apertures with or without shading elements (near-field obstructions) and rooms. f) solar gain – for calculating the net flux through apertures of the building model based on solar-optical glazing properties. For the more advanced profiling levels (those that go beyond solar gain modeling), the following tools are tentatively planned as future extensions: g) surface conditions – for calculating the resultant radiant air temperatures at building surfaces given ambient air temperatures and surface absoprtances. h) thermal envelope – for performing preliminary assessments of thermal quality by applying mean conditions to a basic description of thermal conductive properties. i) transition to simulation – for the pre-processings of solar flux and temperature data for use as driving functions in thermal performance simulations (diurnal/annual). The calculation modules of the solar toolbox prototype are currently programmed as Java applets, which are flexibly embedded in an HTML user-interface referred to as the solar workshop [7]. Since both the solar profiling method and the algorithms behind it are globally applicable, the main objective of this Internet-based implementation is to open the development base and make the "work in progress" as widely accessible as possible to trial users – without the usual hassles of physical media distribution, installation, and security risks on the users' part.


The tools available in the online solar workshop are organized in separate main frames for input by level and an overview of associated output options, whereby the completion of each input level activates a further set of graphic output options (fig. 3). The opportunity to document input parameters and numeric results in tabular form (HTML) is also given in connection with each level. Two additional frames are incorporated for related "Help" information as well as project handling. Since the modeling sequence is intended to accompany the building design process in an on-going fashion, a general case manager tool allows for the saving, loading, and editing of previously entered project data.

Figure 3:

Screenshot of the online solar workshop.


3.

SUMMARY

The solar workshop houses an Internet-based version of the "solar toolbox," that is, a set of solar data calculation programs currently in development, which support the modeling of solar radiation, shading, and solar gain through glazing. The emphasis of the proposed design-guidance application is on graphically profiling buildings in a manner that is highly specific with regard to site location and urban situation (surrounding buildings and other solar obstructions), yet consistent with the schematic nature of early design stages. The solar profiling method itself follows a parametric principle of model generation, applied to areas of solar gain modeling within the framework of an overall thermal simulation model. Employed in parallel with the development of the building design, the information thus yielded by the solar model is also progressively refined, and ultimately serves as reliable preliminary data for comprehensive building performance simulations. Full information regarding the research in progress, including access to the first-level prototype of the solar workshop, is currently available online via the bau><studio website at – http://baustudio.com ACKNOWLEDGEMENTS The author would like to express her gratitude to the Austrian Science Fund (FWF) for supporting the research project titled Integrated Methods of Passive Solar Building Design, in association with the Institut für Hochbau für Architekten (dept. head: E. Panzhauser) of the Technical University of Vienna. REFERENCES [1] [2] [3] [4] [5] [6] [7]

Rudy, M. (1996) Designing Solar Design Tools, Proceedings: Energy and Mass Flow in the Life Cycle of Buildings, International Symposium of CIB W67, Vienna. Balcombe, J.D. ed. (1992) Passive Solar Buildings, The MIT Press, Cambridge. Rudy, M. (1997) Sun and Climate Modeling for Thermal Simulation, Proceedings: Building Simulation '97, International Conference of IBPSA, Prague. Rudy, M. (1998) The Sun, Climate and Architecture: A Proposition for a Solar Design-Support System, Dissertation, Technical University of Vienna. Krec, K. and Rudy, M. (1996) Thermal Building Simulations for Design Practice, Proceedings: Energy and Mass Flow in the Life Cycle of Buildings, International Symposium of CIB W67, Vienna. Rudy, M. (1998) Informing Solar Building Design in an Urban Context, Proceedings: REBUILD the European Cities of Tomorrow, 2nd European Conference, Florence. Kornicki, T. and Rudy, M. (1998) The Solar Workshop, WWW publication: baustudio.com/workshop/Welcome.html.


“Solar Radiation in Early Building Design Stages” - manuscript