While all of the above have been useful, the newest generation of daylighting software combines all of the above and provides the designers with the most flexibility in setting up simulations. It also provides the best information back for making design decisions and adjustments. It is based on input from drawings or models (electronic or physical) and can help identify ways to create optimal daylighting conditions that benefit the users or occupants of the buildings. It can also provide information related to the thermal performance of the daylighting systems and how they impact the total building energy performance. The latest software allows for a variety of simulations including, annual illuminance, point-in-time, and glare distribution simulations such as UDI, sDA, ASE, and DGP. The results can be used for analysis and documentation to qualify for points under LEED and other green building standards. By including simulations for EML, the needed documentation for WELL points can be achieved based on spectral sky calculations for virtually any location.

The progress made in the software and techniques to simulate daylighting in buildings mean that some excellent tools are available to design professionals to accurately predict daylighting performance in all of its forms. However, there remains a critical point that must not be missed. All simulations are based on the data and values that are input. Weather and climate data generally come from reliable outside sources through the U.S. Department of Energy; the correct location just needs to be entered into the simulation.

The information related to the specifics of the daylighting systems, however, need to come from the design team. This means the data must be properly selected from the intended materials to be used. Often, this requires getting the data from manufacturers. In these cases, it is critical that the glazing materials in particular have been tested and independently validated for the quality of light that comes through those materials. In addition to simply the percentage of VLT, the spectral distribution (coloration) and the diffusion characteristics need to be known and accurately put into the simulation. Keep in mind that any given manufacturer usually has a range of different products or options that have different daylighting characteristics, which is good to allow customization and fine-tuning of the design. However, it also means that if different products are being used in different parts of a building that the correct values are put into the simulation. Further, when using a combination of products from different manufacturers, recognize that not all manufacturers test and validate their products the same way. Each one needs to be assessed for the correct values to place into a simulation.

As an aid, some manufacturers will offer a service to architects to perform the daylighting simulation using their products and compare it to other commonly known products. This helps assure accuracy of the simulation and saves the architects from needing to maintain a separate daylighting software program. Discussions and review of manufacturer’s capabilities in this regard should be undertaken before using such a service, of course.

Conclusion

Daylighting in buildings has gained increasing significance in recent decades. Human benefits of health and wellness have been documented, and systems have been advanced that help optimize energy performance. At the same time, advancements in the ability to simulate the performance of daylighting designs in buildings now allows architects, owners, and building users to all benefit from sophisticated, balanced, and appealing daylighting design. This all means that designers can put science behind the art of daylighting to show results in advance.

DAYLIGHTING CASE STUDY

Images (clockwise from top left): courtesy of Kalwall® Corporation; © John Sinclair; courtesy of Kalwall® Corporation

Project: Watt Heritage Centre, McLean Museum
Location: Greenock, Scotland

The Project: The Watt Heritage Center is named after Scottish inventor and engineer James Watt, who is attributed to improving the steam engine and bolstering the industrial revolution in Europe and the United States in the 18th and 19th centuries. The building is part of the McLean Museum and Art Gallery, founded in 1876, which hosts works of art, history, culture, and invention, with the Watt Center serving as a primary focal point. This nationally listed historic building boasts a central two-story gallery with balcony-style display area around the perimeter of first floor that overlooks the display area on the ground floor below.

The Challenge: Reflecting the technology and innovation of the 19th century, the building was originally constructed with a vaulted roof and a large glass and steel-framed skylight that ran the length of the main gallery. It was soon determined, however, that the abundance of sunlight was causing harm and deterioration to many of the museum objects on display. Therefore, during the 20th century, the glass was covered over, making the large, open display space notably darker and much less inviting.

The Solution: The museum underwent a refurbishment that took three years and cost 2 million British pounds to complete. The Glasgow, Scotland-based firm of Collective Architecture was charged with overseeing the work and decided to investigate the options and possibilities of restoring the original skylight. Because of the historic listing, additional reinforcing could not be added, so a lightweight glazing solution was needed. Accordingly, the design team preferred lightweight FRP sandwich panels. Through the significant help of computer simulations, it was able to model the space in three dimensions and establish the solar orientation and available daylight based on historical weather data. Then, it selected specific glazing materials to insert into the computer model to determine the difference in light quantity and quality between different glazing options.

Using glass in the computer-simulated roof produced an average ground floor light level of 566 lux with a range from about 500–1300 lux throughout the area. The upper level was a notably brighter a range of about 1200–4900 lux. Recognizing that much lower light levels would be preferred (on the order of 300–400 lux) to provide a reasonable degree of light without threatening the collections, the architects modeled other materials. Fiberglass-reinforced polymer (FRP) panels offered some appeal since the amount of visible light transmission could be adjusted and controlled. When FRP panels with only 5 percent light transmittance were modeled, the results were the most favorable: an average ground-floor value of 141 lux and first-floor value of 397 lux. Further, the range of variation in the space was minimized, measured at 62–409 on the ground floor and 157–600 on the first floor. This meant the computer model was allowing for the diffusion of light as caused by the FRP panels. The simulations also showed that virtually all of the areas on the first floor and most of the open area on the ground floor were able to rely on only daylight (i.e., daylight autonomy) for more than 60–70 percent of the time.

Images courtesy of Kalwall® Corporation

Daylighting simulation outputs

Based on these detailed, product-specific computer simulations plus the weight restrictions, the design team went ahead and specified FRP panels with 5 percent light transmittance to replace the existing materials in the skylight. Their installation was carried out during the refurbishment of the museum building.

The Results: Justin McNeil of Collective Architecture comments, “I am very happy with the end result, as is the client. Light levels are ideal, and the transformation of the space is substantial.” Clearly, the computer simulation was used to accurately predict the outcome and create these very desirable results.

End Notes

¹Turan, I., Chegut, A., Fink, D., and Reinhart, C. “The value of daylight in office spaces.” Building and Environment. 15 January 2020. Web. 24 March 2020.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect, consultant, presenter, and author of more than 200 continuing education courses focused on creating better buildings.