The installation and planning involved for Tubular Daylighting Devices (TDDs) to deliver natural light to building spaces may seem simple: cut a hole in the roof, pop it in, attach its reflective tubing and, voila! The technology provides supplemental light for one-story, high-bay, or second-story building spaces.
However, while this may have been the case in the past, recent advances, particularly in optics, have led TDDs to evolve and transform from an alternative opportunity for top lighting, into an illumination infrastructure system—one as mechanically complex as any plumbing or HVAC system. TDDs are no longer restricted to traditional zones associated with top lighting. Now, TDD systems can penetrate deep into building spaces as never seen before. More notably, particularly for roofing contractors, they provide an opportunity for future work in that same building, whether it be in addressing churned or reconfigured spaces, retrofits or even buildings being adaptively reused.
How? The technology’s familiar optical “light tube” delivery mechanisms are not limited to moderate tube lengths for daylighting interior spaces directly below the roof, nor must original ducting remain in the same place or have the same configuration over the building’s life. In other words, when a space changes and building managers desire their installed top lighting to migrate or adapt with the people it serves, the infrastructure of a TDD’s optical tubing layout and configuration is reconfigurable without having to move or alter any of the TDD solution’s rooftop assemblies.
This is a huge development in the functional architectural daylighting process. In addition, TDDs can provide full-spectrum daylight for designers and builders to create transformational opportunities for top lighting solutions. Unlike electric illumination, skylights and TDDs deliver all colors of the visible lighting spectrum—an important biological health factor for humans often staying indoors without access to the outside world’s light. To date, the one major advantage electric light had over daylighting solutions was precise control of light placement within the occupied space. This is no longer the case. By applying advanced optical Fresnel lens technology to TDDs, manufacturers have created a daylight lighting “fixture,” although “diffuser” is the correct technical term. This diffuser can deliver precisely controlled placement of light to create consistent visual effects for the occupants.
TDD Guidance from FGIA Documents
Combine these new benefits with the energy savings and sustainability goals daylighting can help provide, and it is no surprise the introduction of such an option has created a positive buzz within the architectural engineering consultant community. To gain insights into the technical detail of TDDs, the Fenestration and Glazing Industry Alliance (FGIA) offers a free downloadable resource: AAMA SKY-3-20, Skylight Selection and Daylighting Design Guide including Unit Skylights, Tubular Daylight Devices (TDD) and Sloped Glazing. It is a comprehensive technical document full of information relating to daylighting and the use of skylights, including TDDs.
Additionally, FGIA’s AAMA 1607-14 document, Voluntary Installation Guidelines for Unit Skylights, offers good water management and installation practices for roof deck-mounted, top lighting. It is available for purchase in the FGIA Online Store.
Lighting Lab Comes to Life
The recent advances in TDD technology can be seen as a rare silver lining of the COVID-19 pandemic. At COVID’s start, TDD manufacturer Solatube International, Inc., a Kingspan Light + Air company, pioneered precision daylight control with advanced optical diffuser technology. The company already had experience with optical daylighting.
Arizona-based DPR Construction applied these advanced optical TDDs as a core energy-efficient, sustainable design component of its net-zero energy office in Phoenix. A key element of the TDD daylighting solution applied to the DPR offices was a combination of advanced optical diffusers, each having unique light distribution and visual appearance characteristics. Designers can now mix and match an array of optical diffusers to deliver narrow, wide or super-wide distribution patterns of daylight.
As a modern fenestration solution, optically enhanced TDDs can address several problematic daylighting challenges, such as glare and shifting patterns of light. Advanced rooftop optics coupled with optical daylight fixture diffusers enable the system to provide desired interior light levels under varying external environmental conditions.
The daylight research and numerous studies of Lisa Heschong and the Heschong Mahone Group have shown daylight drives humans, not only psychologically, but also physiologically. For many people, reduced exposure to sunlight during the shorter winter days results in Seasonal Effective Disorder (SAD). SAD is a form of depression caused by a disruption of the body’s natural rhythms and potentially leads to chemical changes in the brain. It also is the norm, now that human health and sustainability remain at the forefront of architects’ minds.
Technical Matters that Matter
The evolving ways TDDs can now be employed is exciting. That said, technical issues can arise. For example, when dropping TDD tubing deep into spaces, the system can lose efficiency over long tubing distances. Therefore, roofing and installing contractors should keep these three elements in mind to ensure good installation:
Capture Zone. There are many ways to harvest daylight from rooftop apertures. Selective optics can be employed to not only increase the daylight harvested, but also can provide a means of capturing and focusing light, even from low in the horizontal plane. Doing so can extend the hours of useful interior daylight being delivered.
Transfer Zone. This refers to light traveling down the internally reflective tubing from the roof deck to the ceiling plane. This process plays an important role in how captured sunlight transfers to the diffuser. It also involves wavelengths. Within the tubing itself, the most important factor to calculate is the number of bounces a ray of light makes as it moves through the optical tubing system. With each reflection, some light is lost, so carefully considering and appropriately choosing products with high specular reflectivity for visible light is a critical component for daylighting solution success.
Delivery Zone. Lighting designers can often struggle with balancing electric and natural light. However, with the optical control that advanced TDDs provide, many options are now available and can be used to create different layers of light for carefully curated visual environments. More importantly, when advanced optical diffusers are used, the light distribution pattern does not change.
A Transformational Technology
There are numerous additional benefits to TDDs. They can lead to significantly reducing HVAC use with a higher performing building envelope. TDDs can deliver a 50 to 75 percent reduction in rooftop space required for the daylighting solution — a major consideration in establishing a harmonized photovoltaic solution. Efficient use of TDDs can also result in 40 percent less photovoltaic devices being necessary the first place, due to the reduced electric lighting load required during daylight hours. Additionally, LED-integrated TDDs are available, which allow the TDD daylight fixture to provide effective electric lighting when exterior daylight levels start to wane.
TDDs are truly a transformational technology. They are changing top lighting from being a process where a few strategic points of fenestration are placed in the ceiling to an advanced building science that allows for precision control without sacrificing the spectral biological benefits of the sun. TDD technology is an advancing field offering roofing and installing contractors more options and flexibility to offer their clients.
ABOUT THE AUTHOR: Glenn Ferris is the Fenestration and Glazing Industry Alliance’s (FGIA) Fenestration Standards Specialist. Ferris is a liaison for many councils, committees and study/work/task groups guiding them in the completion of the scope of each group. He can be contacted directly at [email protected].
Resources
- AAMA SKY-3-20, Skylight Selection and Daylighting Design Guide including Unit Skylights, Tubular Daylight Devices (TDD) and Sloped Glazing, is available from the Fenestration and Glazing Alliance (FGIA) and may downloaded for at no cost from the FGIA Online Store, www.fgiaonline.org/store.
- AAMA 1607-14, Voluntary Installation Guidelines for Unit Skylights, also is available from FGIA and can be purchased at the FGIA Online Store.
- For specific TDD installation tips, visit YouTube and search for Solatube installation videos.
- Solatube Installation Video Tutorials – Solatube Daylighting Systems
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