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Generative Design with Daylight Analysis, Part 2

Alan Scott Elliot Glassman

Last month, we reviewed some of the health and productivity benefits of daylight and views in buildings, and introduced the important role of daylight analysis as a generative design tool to optimize daylight while minimizing glare. In contrast to evaluative analysis, this includes the proactive use of daylight modeling to inform building massing and configuration, and the use of parametric analysis to inform façade designs, including optimized window-to-wall ratios and shading devices. This month, we are expanding on that theme and illustrating the potential of generative design using a few case examples. These projects demonstrate the power of daylight analysis to inform early design decisions, and optimize daylighting and visual comfort while the building form is still malleable.

Orientation and Massing

There are many factors that influence the orientation and massing of a proposed building, from zoning and code, to program and context, to aesthetic and sculptural aspirations. Quantitative consideration of the impact of design decisions on daylight and views is often left out at this formative stage, which is unfortunate, given the central role this will play in the satisfaction, comfort and productivity of occupants for the life of the building. Generative daylight analysis can easily be performed at the concept phase to inform massing and orientation decisions along with the other factors, as seen in the following urban office tower design.

Tower Massing Analysis, image courtesy of WSP

The architect had generated three alternative approaches to the site plan and massing. The daylight analysis used scripting to divide the massing of each proposed concept into floor plates and parametrically assigned façade properties (such as window-to-wall ratio) to each surface. The modeler ran annual daylight simulations to create a comparison of the daylight potential of each of the three schemes. The analysis revealed that some parts of the massing were too deep to provide adequate daylight to occupied floor areas. It also identified the optimal window-to-wall ratio for each façade. This analysis gave the architect and owner quick feedback to inform the selection and refinement of the preferred scheme. The parametric simulation of window-to-wall ratio and visible light transmittance also showed the sensitivity those parameters will have on building daylight performance.

Façade Optimization

In another example at the schematic design phase of an office tower in a hot climate, the owner and architect were debating glazing options. The owner suggested dark glass to reduce the solar loads, while the architect was pushing clear glass to increase daylight and views. The architect devised a concept for an exterior shading screen that would address both concerns. The building performance specialist developed an integrated performance modeling approach that connected multiple simulations together to validate and optimize the exterior screen concept.

Analysis Flowchart, image courtesy of WSP

This computational design model factored in use of blinds by occupants to control glare, and the subsequent impact that would have on available daylight, and how that would in turn increase electric lighting usage in the energy model. The simulation also parameterized the exterior screen configuration (spacing and size of members) and the visible light transmittance of the glass, looking at multiple options for each building orientation, allowing the architect to fine tune the design in response to the simulated impact of each alternative on daylight autonomy and modeled energy use.

Office Tower Exterior Screen, image courtesy of SOM

The analysis demonstrated that the solar protection of the exterior screen provided multiple benefits. The occupants will pull down the shades less often in response to direct sun, preserving daylight and views for many more hours of the year. Since the screen also reduces solar loads, this allowed the architect to select a more transparent glass, bringing more indirect daylight to the interior. The modelling also quantified the benefits to energy use and peak load reduction, allowing the owner to weigh these against the additional cost of the screen.

Preserving View and Controlling Glare

By virtue of its location and programmatic requirement for visual connectivity (security and openness to public space), a transit center project included a large wall of west-facing glass. It was clear that the high level of direct sun penetration would create a real problem with glare and heat gain, as well as jeopardizing desired LEED credits for daylight. The building performance analysis developed and performed a parameterized façade analysis to study ways to mitigate the glare and heat gain while preserving views and transparency. The parameters included exterior shading devices, the visible light transmittance (VLT) of the glass, and switching some glazed areas to light diffusing translucent glass.

Transit Center Parametric Analysis, courtesy of WSP

The automation of the analysis allowed the rapid simulation of 70 combinations of these variables, which identified a few options that worked best to bring direct sun penetration down within the limits set by LEED, and allowed the architect and owner to visualize the results. The analysis considered tradeoffs between the VLT of the glass and the required depth of shading devices, as well as identifying the best locations to strategically insert translucent bands of glass, helping to hone in on the optimal approach to reduce glare and preserve views in and out.

The common thread in these examples is using a combination of computation design tools and scripting to quickly and automatically generate and analyze design options with multiple parameters. Rather than responding to a design after it is set and trying to mitigate problems, the generative design analysis process can efficiently and effectively inform the conceptual design process in real time, helping architects realize their visions and owners achieve their goals.

Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 30 years of experience in sustainable building design. He is a Senior Associate with WSP in Portland, Ore. Elliot Glassman, AIA, NCARB, LEED BD+C, CPHD, is an architect and specializes in computational design and analysis for daylight and energy in passive buildings. He is an Associate with WSP in New York, NY. To learn more, visit and follow Alan on Twitter @alanscott_faia.