Whole Building Approach to Interior Roller Shade Fabric Selections

Many factors impact building performance, energy efficiency, and aesthetics
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Sponsored by Draper Inc.
By Barbara Horwitz-Bennett

Building Orientation

Playing a significant factor in shading specifications is the facade orientation. To address variances in the sun’s exposure, solar heat gain levels, and the potential of glare, architects will often vary the openness factor based upon the building exposure.

As a general rule of thumb, a higher openness factor shade fabric will typically be selected for the north facade, which receives minimal direct sun. The south and west facades, however, are the most exposed to direct sunlight during working hours, so a lower openness factor is needed.

“A north-facing orientation is almost glare free, so the focus should be on selecting shade properties to maximize outside view, while a west orientation could suffer from low sun angles in the evenings,” Tzempelikos explains. “Therefore, the shade openness factor and visible transmittance should be lowered to protect from direct sun glare.”

As a general example, Adams says that his team might choose a shade fabric with 1 percent openness on the east and west sides of a building, 1–3 percent openness on the south side, and 3 percent openness or potentially no shades at all on the north side. At the same time, spaces like conference and training rooms might require complete light-blocking shades, and other spaces such as medical exam rooms might need privacy, which would necessitate a shade material with 1 percent openness.

For facade orientations that never or rarely experience direct sun, Andow says that a higher openness factor of 8–12 percent can be used unless there is significant glare expected from what he describes as diffuse sky brightness in high solar climates with a turbid atmosphere. “These are all generic rules of thumb, but unique instances require climate-based daylighting models to more accurately predict the probability of discomfort glare,” he explains.

Andow offers an example of a recent office retrofit where a higher openness factor was selected. Manual roller shades in a northwest corner office had created a situation where staff within two desks of the windows were uncomfortably overheated all summer and struggled with glare issues throughout the year. EYP specified an automated 2 percent shade fabric on the west and 8 percent on the north with an aluminized coating on the exterior face of the fabric to reduce solar heat gain. “The staff was noticeably cooler during the summer months, and work disruptions from glare were eliminated throughout the year,” he says.

Photo: Brett Drury, Architectural Photography

Fabric color and automation are important tools in presenting a uniform exterior aesthetic in keeping with an architect’s original vision without creating visual distraction.

Lighting

Because raised shades and higher openness factors impact natural light levels, and when the shades are down, they act as a wall material and contribute to the overall light reflectance of the space, lighting plays into the mix of roller fabric selections.

“We typically have selected the shade material before finalizing the lighting to factor in the amount of natural light entering the space,” explains Adams. “The color value of the chosen shade material, along with other materials in the space, are given to our lighting consultants who take them into consideration when determining the number and placement of light fixtures.”

Architects and lighting consultants also consider daylight-harvesting sensors to optimize interior lighting and daylight balance, capture energy savings, and maintain views. One common pitfall from capitalizing on the benefits of daylighting harvesting is when the shades are always pulled down. To address this, Angarano recommends user training. In addition, motorization and automation may be considered as a way to maximize daylighting benefits.

As noted, glare is a significant issue to address in daylighting designs. The WELL Building Standard defines glare as excessive brightness from a light source, excessive brightness/contrast, and excessive quantity of light. Versant Health, a health-care provider specializing in vision and health, describes glare as the loss of visual performance or discomfort produced by an intensity of light in the visual field greater than the intensity of light to which the eyes are adapted.

Though dated, a well-known 2003 California Energy Commission study is still cited to demonstrate the negative impact of glare on worker performance. Heschong Mahone Group documented the performance levels of office workers at the Sacramento Municipal Utility District. They found an inverse relationship between the glare potential from primary view windows and office worker performance in these settings. In fact, productivity dropped 15–21 percent in the presence of glare.

Of course, glare negatively impacts occupant comfort as well. For example, it can be very difficult for mechanical systems to effectively manage the effects of sunlight directly falling on an individual person sitting in front of the window. With proper shading in place, this enhances personal comfort by mitigating the effect of direct sunlight on occupants.

Modeling Tools

In addition to issues and variables like glare, geographic location, building orientation, glazing, and view, daylighting metrics including useful daylight illuminance and annual solar exposure can guide roller shade specifications. Consequently, daylight and energy modeling programs can be useful tools for designers.

“Today, we have reliable daylight modeling tools that are able to reasonably predict the impact of fenestration on interior lighting conditions and visual comfort,” states Tzempeliko. “In addition, we now have widely acceptable daylight and glare performance metrics, calculated on an annual basis.”

For example, Amenta Emma Architects uses Revit and Cove Tool to help visualize how the building interacts with the sun. “We use this information to strike that balance between preserving views and providing shading devices that assist with controlling glare,” relates Adams.

Other popular tools include DIVA, Climate Studio, Ladybug/Honeybee, and IESVE, which are all based on the validated lighting simulation engine RADIANCE with additional functionality from DAYSIM and EVALGLARE.

While Coulter agrees that daylight modeling tools can help to analyze glare potential, he notes that they do not provide feedback related to visual perception and glare. But the application of more complex glare studies, such as daylight glare probability, are used to predict visual comfort for a specific view point in a space.

He explains that shades can be modeled for these different analyses, but accurately modeling the specific properties such as weave, openness factor, and materiality can be quite challenging. “A simplified material property can be assigned with color, total transmittance value, and openness factor. However, these basic descriptions do not account for thickness of the woven fabric, which affects angular transmission of a shade, or any “glow” from the woven strands,” says Coulter.

Andow explains that calculating the total VLT through a window with a shade fabric minimally requires an integrating sphere measurement, but for more accurate modeling, a gonio-photometer is utilized to determine the bidirectional scattering distribution function (BSDF), which identifies how the light is redirected when light reflects and transmits through it.

“For accurate calculation of the total visible transmittance and total solar heat gain coefficient through a glazing system and shade fabric, designers need to use measured scattering data of the fabric with emissivity and conductivity properties of the material,” he says. “Shade fabric manufacturers commonly have this data, and the researchers at Lawrence Berkeley Laboratory have standardized the processing of these complex optical properties in the free software LBL WINDOW, which designers can use to build and calculate the performance properties of glazing systems with fabric shades.”

While this level of accuracy in modeling is possible, it is not always necessary, as not all projects require such intense analysis. In these cases, Coulter says a combination of simplified simulations, mockups of possible shade fabrics, and personal experience is usually sufficient in determining what best suits the project.

Ashley McGraw Architects typically uses Sefaira for daylight modeling, which helps adjust variables such as light transmittance and glare. At the same time, the firm will typically mock up the shades so that the entire room set up, including technology and interior artificial lighting, can be reviewed together with the true daylight conditions, explains Angarano.

“There is nothing more effective than mocking up a range of colors with the correct openness percentages that provide the level of outside visibility and physically experiencing the ability of the shades to mitigate glare for a number of different people,” agrees Lee. “It is difficult to impossible to transpose a modeling program over the feedback from humans.”

Pisklak recommends that the mockup assembly analyzes the shade through the exterior glazing with both internal and external building materials and finishes. “Furthermore, reviewing the mockup outside under daylighting as well as inside helps to inform the best aesthetic solution for both conditions,” she adds.

 

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Originally published in Architectural Record
Originally published in March 2021

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