Is Solar Design a Straightjacket for Architecture?

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ABSTRACT: This paper seeks to investigate whether the precision of design tools used to meet solar requirements, in particular those related to the heating ...
Published in the Conference Proceedings of the 27th International conference on Passive and Low Energy Architecture (PLEA), Louvain-la-Neuve, Belgium, July 2011

Is Solar Design a Straitjacket for Architecture? Tiffany OTIS1 1

Graduate School of Design, Harvard University, Cambridge, USA [email protected]

ABSTRACT: This paper seeks to investigate whether the precision of design tools used to meet solar requirements, in particular those related to the heating potential of sunlight, act as a straitjacket on architectural form. In order to determine this, two groups of students were asked to design massing models satisfying a set of physical and solar criteria, for one particular site. The first, Group A, had no recourse to solar design tools, while the second, Group B, were trained to use the site specific solar design tools that were developed in this paper. These comprise of a diagram showing the intensity of solar radiation incident on vertical surfaces facing all 360 degrees on a site and interactive images showing the amount of time different parts of a model are in shade. The models from both groups were evaluated based on their adherence to solar criteria and geometrical diversity. Group B models showed a lower proportion of solar design deficiencies compared to Group A models, while also demonstrating more geometrical creativity. The fact that the Group B models did not converge onto an optimal solution, they were more diverse than the Group A models, shows that the use of more precise solar design tools actually helps to broaden the range of architectural form. Keywords: solar, constraints, massing, design, tools.

1. INTRODUCTION This paper explores the question of whether the precision of the solar design tools used by architects at the building massing stage significantly constrains the range of forms available to the designer, or if they in fact may broaden architectural expression through the relative ease with which they allow for experimentation and rapid validation of uncommon geometries. When considering sunlight and architecture, the implications are vast, however, this investigation limits its scope to the heating potential of sunlight as it relates to architecture. In order to evaluate how solar design tools may affect form, an experiment is conducted wherein architecture students are each asked to create a massing model for a particular site. The model has a set of geometric and solar requirements and the students are divided into two groups: the first, Group A, which must design using their personal knowledge of solar strategies, and the second, Group B, who are provided with two solar design tools and taught how to use them in order to create a massing model. The models were then evaluated for adherence to solar criteria and geometric diversity. The presence (or absence) of formal variation in the Group B design models compared to Group A models will show whether or not additional precision in solar design can act as a straitjacket on basic architectural massing.

and attempts to illustrate, in one image, the variation of this contextual radiation over the course of the year. The form of the diagram is inspired by Olgyay's axial charts [1] which plot radiation in a circular manner, while the data synthesizes ideas of regionalism, as propounded by Frampton [2] and time as explored by Kleindienst, Bodart and Andersen in their temporal maps [3]. The values shown on a polar radiation diagram are the sum of the direct, diffuse and reflected components of the sun at a particular site. The diagram shows the intensity of solar radiation incident on vertical surfaces facing all 360 degrees (like a wind rose), which is more relevant for early building massing and orientation than a single horizontal value.

2. TOOLS PROVIDED FOR GROUP B 2.1. Polar Radiation Diagram The polar radiation diagram (Fig.1) provides information regarding the particular solar conditions found on a site. It takes into account the effects of local cloud cover, surrounding buildings and landscape features on the intensity of solar radiation

Figure 1: Polar radiation diagram recorded at 3m, overlaid on its corresponding site. Inner ring=winter, centre ring=spring/fall, outer ring=summer, dotted line= 3000Wh/m2/day reference value

The average seasonal daily radiation values (winter, summer and shoulder) calculated at fifteen degree intervals are obtained through a Daysim [4] simulation, and plotted on a circular diagram overlaid on a plan of the building site. The points are joined through a curve, and each season is thus represented by a ‘circular’ shape. The magnitude of the daily radiation falling on a surface facing a particular direction is represented by the distance from the point on the curve that intersects the normal of this direction to the centre point of the diagram. Effects of surrounding buildings on a building site and ideas about optimal orientations for different seasons can be gleaned quickly from this diagram. 2.2. Ecotect Shadow Range Images The built in shadow range module in Ecotect [5] produces hourly shadow images (Fig.2) which are rich in information for designers. On these images, each hour that a surface is in shade is represented by one tone of grey. Thus, the depth of the shade of grey on a given area represents the fraction of time that this area is in shade. From a solar perspective, if the goal is to avoid solar radiation on a building’s facade, then any white or light grey surfaces signal problem areas. (Note that amount of shade is not to be confused with amount of solar radiation; although two equally coloured surfaces receive the same amount of hours of direct light, they do not necessarily receive the same amount of solar radiation.) With these images, the general massing of a building as well as the sizing of architectural elements can be tested rapidly to determine if they are too large, too small, oriented in the wrong way, and so forth, and then adjusted by eye until the desired effect is reached.

must contribute to fulfil the following solar requirements: maximize the amount of sunlight incident on facades and the designated exterior space during the winter, while minimizing the amount of sunlight incident on facades and the designated exterior space during the summer. 3.2. Methodology Students having completed or who are currently in the process of completing a masters of architecture degree were each asked to build a massing model on a particular site according to the guidelines outlined above. Group A, the control group, were asked to complete the massing model using only a stereographic diagram and their own knowledge of best solar design practice. This group represents the ‘typical solar designer’. Group B, the experimental group, received brief training in order to be able to complete their massing models using the polar radiation diagram and Ecotect shadow range analysis images. (In brief, this involves sketching initial ideas on the polar radiation diagram, building a rough 3D model based on these ideas and evaluating performance vis-à-vis the design goals using Ecotect shadow range images, and modifying the model as much as necessary until results are judged satisfactory.) In order to keep designs on an equal footing, all participants were asked to complete their models within half an hour. 3.3. Hypothesis It is expected that the models produced by the Group A will be similar in their formal strategies whereas Group B will exhibit a broad array of arrangements and approaches. The reasoning is that the design tools will provide Group B participants with feedback rendering them more confident in the performance of their models and thus comfortable with straying from the 'tried and true' south facing courtyard form. 3.4. Evaluation Method Before being evaluated, each submitted model is checked for meeting volume and other basic criteria. Then, evaluation proceeds on two faces: the evaluation of solar performance with respect to the guidelines (maximize solar radiation in winter and minimize solar radiation in the summer on both facades and the designated outdoor space) and the evaluation of geometric diversity (facade orientation, orthogonality and courtyard orientation) between Groups A and B.

Figure 2: An Ecotect shadow range image for June 21st

4. RESULTS

3. THE DESIGN EXPERIMENT

4.1. Solar Performance Evaluation

3.1. Massing Model Guidelines

Ecotect shadow range images spanning from 7:00 to 19:00 with one shadow cast every hour are taken of the primary solar facades (east, south, west) and of the designated outdoor space on December 21st and June 21st. They are used to visually evaluate the solar performance of the massing model submissions based on the four performance criteria listed in the guidelines: maximization of sun on

Guidelines for the massing models to be created by the two groups are: a volume of approximately 75 3 000m , within a maximum buildable envelope of 30m x 77m x 64m, meaning that the building volume will end up filling approximately 50% of the buildable envelope. Additionally, an exterior space or courtyard 2 of at least 200m is required. The building's shape

facades in winter, maximization of sun on an exterior space in winter, minimization of sun on facades in summer, and minimization of sun on an exterior space in summer. Each model is given a score of -1, 0 or +1 to describe their performance in each category. In the two winter categories, where the length of day is just under 9 hours, a score of -1 (unsatisfactory) is given for a predominance of 6-9 hours of shade, 0 (successful) for 3-5 hours of shade and +1 (superior) 0-2 hours of shade. While in the summer categories, with a day length of just under 16 hours, a score of -1 is given for a predominance of 0-3 hours of shade, 0 for 4-7 hours of shade and +1 for 8 or more hours of shade. The scores from the model performance analysis were tallied and are reported for Group A models (Fig.3) and for Group B models (Fig.4). Compared to Group A models, Group B models have both a lower proportion of unsatisfactory designs (3.6% vs. 20%) and a higher proportion of superior performance (32% vs. 20%).

4.2. Geometry Analysis The orientation of model facades in terms of two ‘default’ categories was quantified: facades parallel to site boundaries and facades facing south/north. (Note that on this site, street orientation does not correspond to north/south orientation). In these measurements, one unit of facade corresponds to one length of the site. Thus, a model whose four sides are parallel to the site boundaries receives a count of four. Facade orientation in Group A models (Fig.5) is spread, but there is a strong preference for building parallel to the site boundaries. The opposite is true for Group B, where there are no models with a 4.0 designation (Fig.6).

Figure 5: Group A facade orientation

Figure 3: Group A performance graph

Figure 6: Group B facade orientation

Next, models were analyzed visually and their relative ‘orthogonality’ graphed. Models which, in plan view, possessed no right angles received the designation ‘none’. Those which were formed exclusively of right angles received the designation ‘all’. The models which fell in between these two groups were categorized as having either ‘few’ (under 50%) or ‘many’ (over 50%) orthogonal faces. Group A models (Fig.7) show a strong tendency towards orthogonality, while Group B models (Fig.8) are less conventional.

Figure 4: Group B performance graph

Figure 7: Group A orthogonality

Figure 10: Group B angular facade orientation

The range of orientations from which each exterior space or courtyard could receive sunlight was measured. This information was tabulated along with courtyard performance and whether the space was open to the elements or sheltered by an overhang. Both Group A and Group B results show the same preference for openings ranging from south-east to south-west.

5. CONCLUSION

Figure 8: Group B orthogonality

Model facades are further analyzed in terms of their specific orientation. The area of facade area facing in any given direction is tallied and presented as a percentage of the total facade area of the models in the group. By expressing results as a percentage, differences in total surface area between groups A and B do not affect the results. Group A (Fig.9) and Group B models (Fig.10) both favour orientations which are parallel to the street. The orientation of Mode B models is, however, more spread out over the range.

Figure 9: Group A angular facade orientation

Do solar design tools, in their ability to allow architects to be rather ‘sophisticated’ in regard to massing buildings for sunlight, in fact significantly limit the geometric diversity of the architecture that can be produced on any one site? The results show Group B models outperforming Group A models on all counts. The solar performance of Group B models is superior to Group A models on all points in an evaluation of four solar design criteria, showing that the tools are in fact effective. Group B models are also more creative from a geometrical perspective. They orient themselves in a variety of ways in order to optimize solar control and rarely accept the default ‘parallel to road’ condition that was most often adopted by Group A models. The more unconventional geometries of Group B models (not parallel to road / not facing north or south) are also due to the fact that the design sequence, especially the Ecotect shadow range images, allows one to confirm with great speed whether or not an unconventional move works. With such large discrepancies between Group A and B models, in both geometry and performance, it can be concluded that a ‘blind eye’ approach to sunlight design, using general rules of thumb without any recourse to visualizations, is limiting in terms of the array of forms that the architect feels comfortable using, while the instantaneous and highly visual approach of Group B, which provides site and model specific feedback, results in not only better overall performance, but in the tendency to experiment with form. Most important is the fact that the facade orientations of Group B models are actually more diverse than Group A models. If there were an ‘optimal’ solution for this exercise, one would expect the exact opposite result: with the Group B

orientations converging onto one or several key orientations with the Group A orientations being more disperse throughout the range. Since this is not the case, it is clear that there are a variety of ways to design for the sun on a specific site. Hence, given the proper design tools, solar design is not a straitjacket for architecture.

6. ACKNOWLEDGEMENTS Thank you to all of the students who participated in the model building exercise and to Christoph Reinhart for his support and guidance throughout.

7. REFERENCES [1] Olgyay, V. (1973). Design with Climate: Bioclimatic Approach to Architectural Regionalism. Princeton: Princeton University Press. [2] Frampton, K. (1987). Ten Points on an Architecture of Regionalism: A Provisional Polemic. In: Architectural Regionalism: Collected Writings on Place, Identity, Modernity and Tradition. New York: Princeton Architectural Press. [3] Kleindienst, S. Bodart, M. & Andersen, M. (2008). Graphical representation of climatebased daylight performance to support architectural design. Leukos. 5 (1) p.39-61. [4] Graduate School of Design, Institute for Research in Construction and Fraunhofer Institute for Solar Energy Systems (2010). Daysim 3.0 (beta). [WEB] [5] Autodesk (2009). Ecotect Analysis 2010. [WEB] Autodesk Inc.