Architectural Record BE - Building Enclosure

A New Methodology for Successful Daylighting Design

Selecting fabrics for performance shading
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Sponsored by Lutron Electronics Co., Inc.
Jeanette Fitzgerald Pitts

Shortcomings of the Typical Spec

Here is a very general description of how shade fabric is selected on a great majority of projects. As a fabric, it is often addressed during the furnishings and finishes stage of the job. A large fabric binder is placed in front of the design team, and the fabric for the space is selected based on the color that best complements the interior d├ęcor. Sometimes a specifier will select an openness factor based on a general rule of thumb, or the successes and failures learned from previous projects.

Unfortunately, the color and style of a shade does not dictate its ability to mitigate glare, preserve view, or promote daylight autonomy. This aesthetics-based selection process opens up the interior space to greater potential problems with glare and increases the likelihood that outdoor views will be unnecessarily compromised and energy savings limited. When color is the key consideration in selecting a fabric shade, specifiers are likely to get a product that looks good on the wall but may not manage daylight in an appropriate or satisfactory way. Performance and the fabric properties that drive performance, such as openness factor, visible transmittance, and solar reflectance, must be included in the specification process for optimum results.

Performance-based Specification Process

A more rigorous specification process will enable specifiers to better match the performance of the shade with the needs of the space and select a shade fabric that is aesthetically pleasing as well. The steps in this process are: prioritize performance goals, simulate fabric performance, identify and select an optimal fabric, and write a performance-based specification that communicates design intent.

Prioritize Performance Goals

In order to better match shade performance with the needs of the space, it makes sense to start by identifying the needs of the space. This is especially important when selecting shades because some of the performance goals are at odds with one another. Clearly identifying the priorities of each space enable a specifier to tailor the shade selection to deliver glare protection in spaces where vision-critical tasks are taking place and to allow a crisper view, and slightly less glare control, in social areas.

Typically, work areas place the highest importance on glare control and equal weight on daylight autonomy and view preservation. Transitional areas regularly prioritize daylight autonomy over view, identifying energy savings and a higher level of daylight exposure as the most important goal. Social areas often rank view over daylight autonomy, encouraging specifiers to find shades that preserve color and clarity in these more casual areas. However, goals are project-specific, and that is why it is important to evaluate the unique qualities and needs of each space before selecting a shade fabric.

Simulate Fabric Performance

Across the industry, shade performance simulations can be attempted in a number of ways, but most of them require that the fabric be selected, or at least significantly narrowed down, before the simulations occur. Some projects allow for mock-ups in the budget, which would include an opportunity to test the selected fabric on the mocked-up window. However, mock-ups often fail to capture the actual variability of daylight conditions that exist and may misrepresent the true performance of the shade over the year.

There are several daylight simulation programs that can be used to create virtual models of the building and gauge how daylight will behave in the space given certain material properties and weather data. These simulations are designed to model the daylight in the building one shade material at a time and often do not take into consideration the shade control, albeit automated or manual. Simulating multiple fabrics is a time-intensive process.

Ideally, before spending the time to input several types of fabric into a simulation or reaching the final stage of the mock-up, specifiers would have a tool to identify suitable fabric options for a specific project based on performance criteria.

New Shade Selection Wizard Now Available

A new, free simulation tool is now available to the design and specification community that can provide this performance-based, project-specific analysis in a quick and user-friendly way. This Web-based tool works as a shade selection wizard, where designers key in certain project-specific information, such as the location and facade orientations, window size, glass type, and even a few specifics on the interior layout and function of the space. The wizard then populates a selection of fabrics that will provide the necessary degree of glare reduction, daylight autonomy, and view preservation demanded by the space type.

A new, free simulation tool is now available to the design and specification community that can provide this performance-based, project-specific analysis in a quick and user-friendly way. This Web-based tool works as a shade selection wizard, where designers key in certain project-specific information, such as the location and facade orientations, window size, glass type, and even a few specifics on the interior layout and function of the space. The wizard then populates a selection of fabrics that will provide the necessary degree of glare reduction, daylight autonomy, and view preservation demanded by the space type.

Select an Optimal Fabric

This more rigorous specification process offers specifiers a way to balance aesthetic preference with performance. Once the fabrics that will perform as needed have been identified by the Web-based wizard, a designer can select the fabric color and style that will provide the best aesthetic complement to the space.

Write a Performance- Based Specification

As previously mentioned, a typical shade fabric specification identifies the color and, sometimes, the openness of the fabric. This relatively scant description can leave the specification open to an unsuitable product substitution that could jeopardize the success of the space. This happens for two reasons. First, an openness factor is not a universal metric, and specifiers can get hung up relying on the general approximation, often listed on the fabric cards, instead of the mean openness factor, which is a much more accurate measurement of shade openness. Second, two fabrics with similar perceived colors and similar listed openness factors can, and often do, have very different Tv values and, subsequently, perform very differently in the space. Specifiers should be wary of accepting a fabric as equivalent if its fabric properties have not been tested and if the fabric has not been proven to perform in a manner that is equivalent to the fabric that was originally specified.

Performance-based specifications include the mean openness factor, the Tv value, the Rs value, and the color. This would also be the place to include any certifications that may be required by code or to satisfy green building initiatives, such as PVC-free certification, GREENGUARD certification, or RoHS certification. The selection wizard not only helps in identifying appropriate shade fabrics, but it provides all of the information necessary to write a performance-based specification.

 

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Originally published in Architectural Record.

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