Parametric Solar Architecture

Ecoscape / Rapid-prototyped surface of landscape event / FRAC Centre Collection

Parametric Solar Architecture Building Integrated Photovoltaics

Introduction to Parametric Thinking Design Principles and Methods III

Cardiff University Welsh School of Architecture Arief Afandi Thomas Wakeman Eric Wong

The Role of Parametrics and BIPV Systems It is becoming increasingly important in the design of the built environment to generate integrated systems which optimise off-grid energy systems and environmental control. Parametric design plays a vital role in the burgeoning field of Building Integrated Photovoltaics (BIPV’s), a system that sandwiches photovoltaic cells between two layers of glass, creating a building enclosure system where the wall or roof is the photovoltaic surface, reducing the redundancy of traditionally roof design. With potential beyond the capacity of traditional photovoltaics, parametrics become much more than a simple form finding exercise, and begin to manipulate complex genetic algorithms in instances where it would be impossible to evaluate manually. Based on solar geometry, optimal surface designs can be achieved for solar collection or shading, creating buildings designed specifically to maximise environmental performance.

Methodology The Algorithmic Design Method & Macroscale Design The concept is to define the macroscale component of a solar capturing surface, using generative components to create an entire roof form. This method deploys a genetic algorithm from which data is extrapolated from a planar surface (e.g. a flat photovoltaic panel). A Computational Parametric Interface, (CPI) makes comparisons between curved and flat surfaces according to various sun-angle settings (tilt angle and azimuth angle) familiar with climate analysis, as well as solar condition setups (latitude and radiation mode). A stereolithographic approach is then used to generate an optimised nurbed surface geometry for the design.

A useful analogy is to think of some of the fundamental principles of evolution:

“In each generation, the fitness of every individual in the population is evaluated, multiple individuals are stochastically selected from the current population (based on their fitness), and modified (recombined and possibly randomly mutated) to form a new population. The new population is then used in the next iteration of the algorithm.

Commonly, the algorithm terminates when either a maximum number of generations has been produced, or a satisfactory fitness level has been reached for the population.”

Ecoscape, a proposal for a research center in the Californian Mountains by Open Source Architecture uses this principle in a situation where the building must operate entirely off-grid.

Ecoscape’s skin is constituted of printed BIPV cells. Its surface geometry maximizes solar exposure by responding to a wide range of environmental parameters. These parameters are integrated to an algorithm that transforms and optimises the surface geometry, creating areas of the roof that distort to the optimal efficient angle in relation to the sun. The CPI system assures stability of the ratio between the PVcells’ energy reception and the sun’s intensity.

Inbetween the BIPV, the roof will be clad with Texlon Foil Systems. The foil is transparent and has high durable features, in addition to its lightweight or insulating properties, and much like a reactions glasses lense, has the capability to adjust its shading, thermal, and aesthetic characteristics as the sun moves across the sky.

A Geometric Cladding Approach: Retrofitting and Microscale An alternative field of study is the application of BIPV’s in retrofitting and proprietary installations, where the building form is already defined. In this instance, as it is not possible to define a large scale optimum geometry, it is important to focus on the design of the microscale surface, allowing a smaller scale form which could be applied as a cladding or panel system.

The Vela Roof project in Bologna, designed by TUDelft Research Project deployed a Tesselated surface of small scale undulations which can be evaluated as triangles.

Combined as a printed surface on ETFE, with alternate opaque pv and transparent surfaces, this method creates a different curvature to each side of a panel.

Application in the Built Environment:

Case Study: The Vela Roof (Bologna, Italy) - TUDelft Research Project An example of microscale optimisation of BIPV’s, The Vela roof is part of a larger project currently under construction in Bologna, Italy. The case study exemplifies the importance of geometry in additionally regulating climatic comfort, specifically in the direct exposure and daylight factor of the spaces underneath the roof. It also focuses on passive strategies for reducing the summer overheating of the spaces underneath the roof.

Interior rendering of the Vela roof, Italy( currently under construction)

In order to explore geometric design alternatives, parametric modelling was used to define the relationship between geometrical entities and their relationships. At the microscale, various options were explored for the cladding system in order to reduce the direct solar gain internally whilst maximising indirect natural light.

The structure consists of a surface comprising quadrangular polygons arranged at vertices, constructed from an ETFE module, based on these polygons, NURBS surfaces were built to describe the inflated top and bottom ETFE layers.

The ETFE cladding design, viewed from the north and from the south sides.

Performance-Oriented Parametric Design The cladding system is based on a three-dimensional geometry with a north–south oriented printed shading pattern, used to achieve the solar regulation requirements.

A coordinate system assumes an absolute reference that remains constant to describe the position of the vertexes of the polygons.

Parametric modeling of the cladding of the Vela; left) control of direct radiation and indirect light based on printed pattern, parametrically explored for different opening angles; right) shadow simulation emphasizing the reduced transmission of direct radiation.

Periodic pattern of sine and cosine waves Source : http://wn.wikipedia.org/wiki/Sine_wave

2D array of control points follows periodic patterns in both U and V directions

Left: Bezier curve with two control points; right: Bezier curve with eleven control points

Three methods can be used to generate a point grid whose distribution in space is parametrically variable: 1) Positioning the points along a NURB surface (macroscale) 2) Distribution of the points along a NURB surface (microscale) 3)Positioning the points using mathematical formulations to describe their positions (non-parametric) The Vela Roof design combines methods 1&2 to effectively create one large curved solar panel with individually optimised micro-tesselations controlling the shape of the roof. The same shape could be used as an individual solar panel for cladding purposes. By parameterizing the entities through which the NURB surface is defined (such as boundary curves, curves to loft, a list of the points that the surface will pass through, control points, or other). By varying the positions or configurations of such entities, the entire surface changes its shape. The second parameterisation regards the distribution of points on the surface, and aims at controlling the density of the grid and its proportional distribution along the directions of the NURBS. One method that can be used to distribute a grid of points onto a NURBS surface is based on the UV coordinates. In this case, the density of the grid and its proportional distribution can be regulated by parameters, which are independent from each other or reciprocally related via equations. A set of scripts can contain these equations, and can be reused whenever a NURBS surface is used as input to generate an array of points.

As a result, the orientation of the pattern of each ETFE cushion is studied to block direct solar radiation and allow the income of indirect light according to its position within the overal panel.

Conclusion

Positioning the points along a NURB surface

Distribution the points along a NURB surface

Parametric and algorithmic thinking can offer automatic solutions to optimise climatic design. Based on geometric variations, the user can specify the location and weather conditions, and the parametric tool will automatically assess a large set of alternative design solutions.

In the field of sustainable design, this gives designers the ability to take existing structures or design entirely new ones whilst exploring a whole range of design alternatives generated with respect to the building’s orientation and optimal solar exposure for its location. This creates the potential for all fields of architecture to reconsider the environmental performance of their buildings, without compromising the most important aspects of comfort, aesthetics and functionality.

Bibliography

Cheng, Sheng. “Curved Photovoltaic Surface Optimization for BIPV: An Evolutionary Approach Based on Solar Radiation Simulation.” Curved Photovoltaic Surface Optimization for BIPV: An Evolutionary Approach Based on Solar Radiation Simulation. Bartlett School of Graduate Studies University College London, n.d. Web. 20 Feb. 2013. <discovery.ucl.ac.uk/18982/1/18982.pdf> Turrin, Michela , Peter von von Buelow, Axel Kilian, and Rudi Stouffs. “Performative skins for passive climatic comfort: A parametric design process .” Automation in Construction 22 (2012): 36-50. Science Direct. Web. 20 Feb. 2012.

Turrin, M, R Stouffs, and S Sariyildiz. “Parametric Design of the Vela Roof.” Parametric Design of the Vela Roof. N.p., n.d. Web. 20 Feb. 2013. <www.google.co.uk/url?sa=t&rct=j&q=parametric%20design%20of%20the%20vela%20roof &source=web&cd=1&ved=0CDIQFjAA&url=http%3A%2F%2Frepository.tudelft.nl%2Fassets%2Fuuid%3A717717af55dd-4e3c-8ba1-951575e200d9%2F279327.pdf&ei=EgYlUeyUEOik0AX7toCoDw&usg=AFQjCNFN1> “arch plus 355: Ecoscapa | Open Source Architecture.” arch plus 355. N.p., n.d. Web. 20 Feb. 2013. <http:// archplus355.blogspot.co.uk/2011/01/ecoscapa-open-source-architecture.html>