How The New VTannual Rating Affects Daylighting

If you’re involved with daylighting commercial buildings, you need to know about optically complex fenestration systems and the new VTannual rating.
   Optically complex fenestration systems are technologically advanced products that use specially engineered light-bending or light-reflecting elements to harvest the wavelengths of light that we want to use to illuminate building interiors. One key example of these new types of optically complex fenestration systems is the tubular daylighting device (TDD), which collects and admits natural light into interiors more effectively than conventional daylighting options.
   Featuring progressive technologies, these optically complex systems use stringent refractive, reflective, and filtering elements to selectively harvest natural light over the course of a year. Compared with traditional skylights, windows, and less-complex TDDs, state-of-the-art TDDs use advanced optics and materials to deliver higher quality visible light with more consistent illuminance, regardless of sky condition or climate. They also significantly reduce the potential for shifting light patterns, glare, and heat transfer issues.

Current rating issues
So how do building designers know which optically complex system offers the best performance for their particular projects? Currently, visible light transmittance (VT) is a factor commonly used by architects, engineers, and contractors to predict a daylighting system’s light output. It’s also a performance rating that is measured using testing and rating protocols established by the National Fenestration Rating Council (NFRC), Greenbelt, MD.
   The issue with the VT rating is that it doesn’t sufficiently account for the light-collection control that can be designed into optically complex fenestration products. These systems are engineered to filter out undesirable wavelengths—such as fabric-fading ultraviolet, heat-carrying infrared, and overpowering midday sunlight—so the collection and transmission of light varies, by design, throughout the day and year. This variance makes product comparisons difficult and the simple VT measurement a poor performance indicator.

Devising a new rating
Measuring simple VT involves direct-normal testing where a single beam of light is aimed into the optically complex system from directly overhead. There are two problems with the test. First, natural light transmits through a surface at a variety of angles throughout the day (depending on the sun’s position in the sky), not just in a perpendicular fashion. Second, this method doesn’t allow the benefits of technology to come into play, such as dome optics or optical tubing reflectance. Every daylighting system performs relatively the same when using this testing protocol, so it does not offer an accurate depiction of a product’s real-life performance. As a result, it doesn’t provide a valuable resource to the consumer when trying to select the best product for a particular application.
   To select the best daylighting system for a given project, commercial building designers must be able to compare product performance with respect to daylighting configuration and geographic location as well as climatic and seasonal variations. Until now, the lack of standard performance metrics that adequately address this new breed of daylighting systems has made the simple comparison and selection of optically complex systems virtually impossible.
   Enter the NFRC Tubular Daylighting Device Task Group. Consisting of members from the NFRC, including technical representatives from the Lawrence Berkeley National Laboratory (Berkeley, CA), testing laboratories, and several major TDD manufacturers, this collaboration has worked for more than four years to develop a new performance testing protocol for collecting and rating visible transmittance data for optically complex systems.
   The outcome of the group’s efforts was a new annualized visual transmittance rating protocol (VTannual), which was implemented by the NFRC in late 2013. The new VTannual protocol offers a more meaningful performance rating that provides an extremely accurate view of how an optically complex system will perform in real-life situations. It will allow building designers to make a true “apples to apples” comparison between daylighting products so they can choose the best system to meet their project goals.

This illustration is a graphical representation of solar angles defined and utilized within the NFRC VTannual rating protocol. Illustration courtesy of NFRC.

This illustration is a graphical representation of solar angles defined and utilized within the NFRC VTannual rating protocol. Illustration courtesy of NFRC.

Calculating VTannual
To calculate the VTannual rating, a specially designed apparatus measures a daylighting product’s:

  • Annual visible transmittance: the annualized amount of daylight transferred through a surface into an interior space.
  • Zonal time (ZT) weighting factors, which are a function that determines the percentage of time the sun spends within a specific patch of sky.

   The apparatus does this by collecting clear-sky, visible-light-transmittance data for a series of vertical planes of data in 10-deg. increments. The measurements span vertical angles for solar altitudes (angles of the sun above the horizon) ranging from 20 to 70 deg. at three specific solar azimuth angles (the compass direction from which the sunlight is coming, i.e., east or west relative to due south) of 0, 30, and 60 deg.

Figure 3 (Figure 2 is not shown) is a depiction of solar altitude angles as measured with respect to the opening of the moveable test apparatus. Illustration courtesy of NFRC.

Figure 3 (Figure 2 is not shown) is a depiction of solar altitude angles as measured with respect to the opening of the moveable test apparatus. Illustration courtesy of NFRC.

   Ultimately, 18 distinct points of paired data are collected, then factored in with the historical position of the sun for a preselected site location which, for the NFRC rating, will be a standard Middle America location at 40 deg. north latitude, i.e., Boulder, CO. These can then be used to generate functional, annualized, visible-light-transmittance ratings for any site location in the world, accounting for how an optically complex product is designed to selectively increase or reduce light collection for specific times of the day and year.
   It’s important to note that the VTannual rating is based on clear-sky conditions only. Thus, the new rating will be less useful for people who live in predominantly overcast or cloudy climates.

Obtaining a rating
To obtain a VTannual rating, a manufacturer works with a third party testing organization to conduct the test. The results are then sent to an independent inspection agency to review and verify the test data and rating results. If the data are deemed to be accurate and conform with the testing standard, an NFRC label with the rating is issued to the manufacturer for use on its packaging. The data are also uploaded to the NFRC Certified Product Database.
   The VTannual rating is designated as a single number that represents the annual average clear-sky visible transmittance of a daylighting product for a standard Middle America location. This accounts for the actual time-weighted path the sun travels during the course of the year, and is expressed as a number between 0 and 1. This differs from the static direct-normal VT rating, also expressed as a number between 0 and 1, which, for a skylight, represents the ideal maximum light transmittance of a product when the sun is directly overhead, a condition that never happens for all but a few hours each year for sites within the tropics near the equator.

Taking a new approach
Optically complex systems are forcing a paradigm shift in commercial-building design. With their ability to collect, filter, and redirect daylight, they have made it easier for natural light to become the primary daytime illumination source, with electric lighting taking a supplementary role. These systems are not your average TDDs, but fully vetted lighting equipment that has been proven to perform.
   The adoption of the VTannual rating protocol is a crucial part of this new approach to commercial lighting. It is a significant advancement in how fenestration products are evaluated because it allows those involved with building design to make educated decisions based on a product’s real-life performance, and eventually the data collected in the NFRC VTannual rating process may even allow annual performance values to be calculated relative to the building’s actual geographic location.
   Architects can now make direct comparisons, which allows them to specify and select the best product for the application. They can even calculate how much useful light is available, making it possible to estimate how much electric light is needed to make up for any deficiencies during any hour of the year. Look for the new performance rating on NFRC labels starting in the Fall of 2014.

Author
Neall Digert, Ph.D., MIES, is vice president of product enterprise, Solatube International Inc., Vista, CA.

Five Myths of Tubular Daylighting Devices

Are these myths preventing you from specifying/purchasing tubular daylighting devices for your commercial facility?

Michael Sather, commercial marketing manager at Solatube International Inc., Vista, CA

Michael Sather, commercial marketing manager at Solatube International Inc., Vista, CA

Many people are familiar with the concept of tubular daylighting devices (TDDs), often generically referred to by more informal names such as solar tubes, sun tunnels, light pipes, or tube lights. The general concept is simple: A dome, attached to a roof with a self-mounted flashing or mounted on a curb, captures sunlight, transfers it into the building through a highly reflective tube, and delivers it into the interior space through a diffuser lens mounted at the ceiling level or at the end of the tube in an open ceiling.
   In the past 13 years, TDDs have revolutionized the way buildings are illuminated. When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on electric lights only as a backup during extremely overcast days or at night.
   That said, how do you know if TDDs are the right choice for daylighting your project? What key aspects should you consider when selecting the best TDD for a specific application? To help answer these questions and give you a better understanding of this product category, let’s explore five myths of TDDs.

When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on the electric lights only as a backup during extremely overcast days or at night.

When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on the electric lights only as a backup during extremely overcast days or at night.

Myth 1: Tubular daylighting devices are only for residential applications or small spaces.
The original TDDs that appeared in the U.S. market in the early 1990s were strictly designed for residential spaces. In the past two decades, the TDD category grew to rival and eventually surpass traditional skylights for residential applications.
   Building on that residential-market success, the world’s first commercial-grade TDD appeared on the scene in the year 2000. This new technology boasted a 21-in.-dia. tube and a transition box for a grid ceiling system, which allowed a round tube to accommodate a square diffuser, simply by replacing a 2 x 2-ft. ceiling tile. Open-ceiling models also debuted at this time and featured a diffuser lens attached directly to the tube bottom. As a result, the approach to daylighting commercial buildings was greatly simplified and the daylight fixture concept was born.

Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior.

Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior.

Myth 2: Tubular daylighting devices are only for the top floor.
Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior. It is often confused with total reflectance, which refers to scattered light that is reflected in every direction. Total reflection is not an indicator of throughput since this would include light reflecting back up the tube.
   When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, only about 5% of the light is lost. This makes possible tube runs of great distances, spanning multiple floors, running down chases in the walls, and using multiple 90-deg. turns to be able to deliver daylight deep into the interior of multistory buildings.

When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, approximately only 5% of the light is lost.

When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, approximately only 5% of the light is lost.

Myth 3: Tubular daylighting devices are only effective at certain times of the day or year.
Factors affecting seasonal consistency are a combination of specular reflectance, dome optics, spectral selectivity, color temperature maintenance (CTM), and solar heat gain. Lower end TDDs will have a greater difference in daily and seasonal variation due to a lack of the above mentioned properties.
   Advanced TDDs offer daily and seasonal consistency by incorporating dome technologies with passive internal reflectors or Fresnel-lens optics to help efficiently collect low-angle sunlight. This can greatly increase performance in the early morning or late day. During the winter months, when the sun is low in the sky, this is an especially important consideration in Northern latitudes.

Myth 4: Tubular daylighting devices are unpredictable.
While dome optics and tubing material will play a major role in the predictability and consistency of a TDD, you must also take into account the overall design. Even the most advanced TDDs can be designed incorrectly into a space. If you use too many units, the results can be overwhelming; if you use too few, the results can be disappointing. Most TDD manufacturers offer daylight dimming devices that provide total control over the amount of daylight entering the space.

Myth 5: All tubular daylighting devices are the same.
This statement is equivalent to saying all cars are the same. To ensure you select the right TDD for your particular project needs, there are three main considerations: the manufacturer, the product, and the partner:

  • The manufacturer. Significant differences exist in the product offerings and core focus of companies manufacturing TDDs. Some manufacturers specialize in TDDs as their sole business, whereas other companies may only offer TDDs as a small part of their overall product line.
  • The product. Be sure to specify a product that meets the needs of the space. Most TDD manufacturers will offer a wide range of models and component options to create the right configuration for the specific application and climate.
  • The partner. Once a manufacturer is selected, it is probably best to make sure there is a factory-trained distributor or representative to assist with the project. Most TDD manufacturers will have a partner who works with you at a local level from project conception through completion to help you meet your daylighting goals and stay within your budget. These companies typically offer installation services as well as installation training for subcontractors to ensure your project is a success.

Michael Sather is the commercial marketing manager at Solatube International Inc., Vista, CA.

Ask Questions, Then Design Lighting

Lighting design should be part of the initial facility design phase to ensure effective illumination and energy savings.

Cheryl Ford, marketing manager for OSRAM Sylvania, Danvers, MA.

Cheryl Ford, marketing manager for OSRAM Sylvania, Danvers, MA.

The intended use for a building and the owner’s design goals not only affect the layout, finishes, and furnishings, but have a significant impact on lighting needs and energy costs. Unfortunately, lighting often is not discussed in the early design stages for new and major renovation projects. If lighting is a part of the early discussions, it is much more likely that the best possible luminaires will be chosen to fit the style of the building and its intended use.
   Discussing lighting early will also help ensure the building’s design can accommodate the desired luminaires and controls to achieve the lowest energy and maintenance cost without sacrificing lighting quality. Before specifying lighting, answer the following questions.
   Who is the end user?
   Is the building owned by a company for its own use or is the space being leased to multiple tenants? For businesses, branding by way of unique building design and layout plays a part in establishing that brand. In addition, exterior and interior lighting are equally important for the safety and well being of workers, customers, and clients. If a building is to be occupied by a single company, it is easier to minimize the number of luminaire types. For leased spaces, tenants often want the space constructed to meet their requirements, and this includes lighting. Lease agreements vary, but tenants often are required to pay utilities on the leased space, so work with them to install the most energy-efficient lighting possible.
   What is the desired style or look?
   Aesthetically pleasing lighting can be modern, contemporary or traditional, and there is a variety of luminaires from which to choose. For an unobtrusive modern look, recessed flat-panel, recessed indirect, or architectural recessed 1×4, 2×2, or 2×4 luminaires can provide a very clean look and uniformly lit spaces. For a more contemporary look, single pendant-mount luminaires can be geometrical, adding an artistic look to the space. There are also more traditional long linear runs of indirect/direct pendant-mount luminaires with an up-light and down-light component providing extremely low-glare lighting. In addition, these luminaires light the ceiling, brightening the look of the space.
   You do not need to sacrifice on the aesthetics of a luminaire just to save energy. State-of-the-art high-efficiency, long-life fluorescent lamp and ballast systems are available in many styles, providing energy savings as high as 40%, compared with standard T8 fluorescent units. Luminaires using LED systems that offer energy savings as high as 50% when compared to conventional fluorescent systems are available.
   How will spaces be used?
   How a space is to be used determines required lighting levels. In the past, however, many interiors have been over lit. Fortunately, the Illuminating Engineering Society of North America (IESNA), New York, has established recommended lighting levels for specific tasks, and following these guidelines will reduce over-illumination and wasted energy.
   The type of space will also dictate the need for additional lighting controls, and this may influence your luminaire choice. Many LED luminaires come with integrated controls for installation ease. Also, layers of light, especially for hospitality and classroom lighting, provide the flexible lighting typically desired. For office environments, the use of task lighting allows overhead lighting levels to be scaled back, reducing energy usage.
   What are the latest energy code requirements?
   ASHRAE 90.1 and California Title 24 have maximum power-density requirements (W/sq. ft.) and mandatory control provisions for interior and exterior applications. The latest versions of each have additional mandatory control requirements. Alterations affecting more than 50% of the lighting load must conform to the codes.
   ASHRAE 90.1-2010 requires space control for enclosed areas with at least one control step between 30% and 70% of full power. Exceptions include corridors, public lobbies, restrooms, stairwells, storage rooms, and electrical/mechanical areas. Various auto-off requirements also are established, particularly for parking garages.
   California Title 24 2013 has added more multi-level control requirements, specified by space type for areas greater than 100 sq. ft. Auto-off requirements are also established for interior and exterior spaces and parking garages. There also are specific requirements for daylighted zones and use of occupancy sensing or auto scheduling. Demand response is now required for all non-residential buildings of more than 10,000 sq. ft.
   When does daylighting make sense?
   There is trend in commercial buildings to use more natural light and provide occupants with outdoor views for health and well-being benefits, as well as to save energy. However, to make daylighting effective, the building design and window selection are extremely important. North/south-facing windows and windows with the proper glazing to minimize glare need to be incorporated into the design. In new-building construction, light shelves and skylights improve daylight use. A window-shading system can effectively control the amount of sun that enters a space. Light sensors and 0- to-10-V dimming is the best way to reduce the luminaire light level in response to available daylight.
   Which lighting technology?
   The cost to install LED lighting instead of conventional fluorescent and high-intensity-discharge technology has decreased immensely in the past several years. LED luminaire performance, controllability, and color quality is equivalent to many fluorescent systems, so for new construction LEDs may be the best choice. For retrofit projects, high-efficiency, long-life fluorescents may be the least expensive option, but do not rule out LED retrofit solutions that use the existing luminaire housing. Utility rebates are available for DLC-qualified (DesignLights Consortium, Lexington, MA) LED luminaires and for high-efficiency and supersaver fluorescent systems, reducing the cost to install the most efficient lighting.
   Lighting can help shape a business and its outcomes in very subtle ways. When done correctly, it can dazzle people, provide comfort, and improve productivity. Quality lighting does not need to break the budget, and it can be very energy efficient. In evaluating lighting options, look at the total cost of ownership. Hire a lighting designer to make sure the best lighting system is designed for the facility.

Cheryl Ford is a marketing manager for OSRAM Sylvania, Danvers, MA. She has
more than 30 years of lighting experience; has held various positions in engineering, marketing, and sales; and is a NCQLP lighting certified professional. Watch for regular lighting columns from Cheryl at cbpmagazine.com/blog.

Daintree, LG reduce wireless LED lighting control overhead

p-LED-LG2Daintree Networks and LG Electronics USA recently announced that they have created a fully integrated LED lighting solution with wireless control for commercial settings. The jointly-developed system embeds wireless communication capability directly into LED drivers used in LG LED lighting fixtures, enabling seamless interaction with Daintree’s ControlScope™ networked wireless control solution. Initial LG products with wireless drivers include LED troffer fixtures and retrofit kits. The resulting joint solution is expected to yield significant savings for users, both in up-front costs and in energy efficiency following installation, benefiting also from the market-leading efficacy of LG LED troffers.

Using wireless LED drivers eliminates both the expense and installation challenges associated with using a separate wireless adapter, which was required for granular wireless control of overhead troffers in commercial and industrial buildings. Daintree estimates that, with the LG-Daintree solution, companies can expect to save up to 85 percent per fixture in equipment and labor for installing wireless communication and improve energy efficiency by up to 90 percent.

Solatube International donates daylighting to educational facilities

solatubeResearch has shown that students benefit tremendously in daylit environments. For example, a study by Heschong Mahone Group for Pacific Gas & Electric Co. tested 21,000 in three states and found those in classrooms with the most daylighting progressed 20 percent faster on math tests and 26 percent faster on reading tests in one year than those with the least. A California Energy Commission study found a 21 percent improvement in learning between those with least daylighting to those with the most.

To support increased daylight in education, Solatube International, is continuing its highly successful program to donate Solatube Daylighting Systems to qualifying schools and colleges in 2014. The program is for PreK-12 school districts and higher education institutions interested in adding daylight to their facilities, up to 10 units per organization. Nineteen of these projects were completed in 2013.

One campus that is already benefiting from Solatube’s 2014 “Operation Textbook” program is Kirkwood Community College. Students and faculty working on the SHEP (Sustainable Housing for Education Project) located at the Iowa Sustainable Village on the Kirkwood Community College campus are demonstrating the latest in sustainable design and construction. The design for the SHEP has been developed by students within the Architecture, Interior Design and Construction Management departments. These same students along with many others at the Cedar Rapids, Iowa, campus have spent the fall and spring semesters building the SHEP with a completion date of May 2014.

Designers or facility managers interested in Solatube International’s “Operation Textbook” program for donated Solatube units can email commsales@solatube.com for more information.