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.

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

DOE awards PPG $2.1 million to help automate PV manufacturing

ppgThe U.S. Department of Energy (DOE) has awarded PPG Industries’ industrial coatings business $2.1 million award to help design and pilot a rapid photovoltaic (PV) module assembly process that uses automation to eliminate time and labor from the current assembly process.

PPG will use the funding, delivered through the DOE’s SunShot Initiative, to develop liquid encapsulants that will enable PV modules to be manufactured without the need for capital-intensive laminators. PPG will match each dollar committed by the DOE, resulting in a total public-private investment of approximately $4.3 million in the project.

PPG is partnering with Flextronics International, Inc., a leading global solar module manufacturer, to design and test a pilot line at Flextronics’ Milpitas, Calif., facility that will produce 60- and 72-cell modules. PPG and Flextronics expect to increase module throughput by a factor of four at half the capital expense of the existing process.

The SunShot Initiative, which is funded through the DOE’s Office of Energy Efficiency and Renewable Energy (EERE), seeks to make solar energy fully cost-competitive with traditional energy sources by the end of the decade. The PPG award is part of a $13 million investment in five projects to strengthen domestic solar manufacturing and speed commercialization of efficient, affordable PV and concentrating solar power technologies.

Sika Supports Solar Decathlon Teams

SikaSika Corporation has donated building materials to the U.S. Department of Energy Solar Decathlon 2011 in support of EMPOWERHOUSE and ENJOY House. The U.S. Department of Energy Solar Decathlon challenges 20 collegiate teams from around the world to design, build and operate solar-powered houses that are cost-effective, energy-efficient and attractive. This year’s college teams displayed their homes on the National Mall in Washington, D.C. from September 23 to October 2.

ENJOY House by Team New Jersey members Rutgers, the State University of New Jersey, and New Jersey Institute of Technology incorporates a new way of approaching high-performance, energy-efficient residential design. The house utilizes precast, concrete insulated panels and passive solar strategies to reduce heating and cooling loads. Sika Corp. donated G410 roofing membrane and adhesive, along with accessories and metal to waterproof the precast concrete deck. The Precast Concrete was produced utilizing Sika’s Viscocrete technology, Air Entrainment and a new product – Sika Watertight Concrete Powder. This combination resulted in a High Performance and Waterproof concrete structure. All of the precast panel joints, windows and doors were sealed utilizing various Sika sealants. The team effort included precast concrete produced by Northeast Precast, the applicator/installer Dumar Services, LLC with Martin Dubois leading the team, and the General Contractor Skanska Construction.

EMPOWERHOUSE is a community-based approach to building affordable, net-zero housing that addresses all aspects of domestic life. This superefficient, solar-powered house was designed and built by architecture and engineering students from Parsons The New School for Design, the Stevens Institute of Technology and the Milano School of International Affairs, Management and Urban Policy. In addition to technical support, Sika AG subsidiaries donated G410 roofing membrane and adhesive, sealants for windows and concrete, admixtures that included a high range water reducer and air entrainment, and a new product – Sika Watertight Concrete Powder. The Sika Sarnafil applicator/installer was Delta Contracting Services led by Chris Dubois.

ENJOY House’s design was aimed at creating an affordable, functional, energy-efficient precast concrete house suited to the climate of New Jersey and intended for a couple that retires to the New Jersey shore. In addition to being ADA accessible, the house incorporates evacuated solar thermal tubes that heat domestic hot water and provide pre-heating for the hydronic radiant floor; high-performing, energy-efficient windows; a photovoltaic system with a daily output of 36 kWh, and energy recovery ventilators and dehumidifiers that keep cool air inside the house while providing fresh air from outside.

The EMPOWERHOUSE team is working with community partners, including Habitat for Humanity Washington D.C. and the D.C. Department of Housing and Community Development, to bring EMPOWERHOUSE beyond the National Mall. The team is constructing a second house in the D.C. neighborhood of Deanwood. After the Solar Decathlon, the two houses will be joined together to create a two-family home, and will be a model for affordable, net-zero housing that can be replicated around the globe.

Entrants must create a house that is affordable, attractive, and easy to live in; maintains comfortable and healthy indoor environmental conditions; supplies energy to household appliances for cooking, cleaning, and entertainment; provides adequate hot water; and produces as much or more energy than it consumes

This is the second participation in such an event for Sika Corporation. In 2009, Sika Sarnafil sponsored a team from the University of Florida, one of only two U.S. participants in the biannual global competition.

North American Manufacturers Form Consortium for Solar Lighting

Consortium for Solar LightingFour manufacturers recently founded the Consortium for Solar Lighting (CSL). The CSL’s founding members are Sharp Electronics Corporation, Carmanah Technologies Corporation, Inovus Solar, Inc., and SolarOne Solutions, Inc.

The mission of this group is to accelerate the adoption of reliable solar lighting technology through the development of universal specifications intended to support customers’ fair and comprehensive evaluation of commercial-scale lighting systems. In the process, the group expects that these specifications will foster awareness of solar powered lighting and the applications where it is a viable alternative to conventional grid-connected lighting technology.

The group is focused on assessment of the energy balance of a system design to ensure operation that is aligned with customer’s expectations. Other aspects of the system design, including standards that apply to individual components of the system, lighting characteristics or aspects that relate to safety are already being addressed through national and international bodies such as Commission International D’eclairage (CIE), Illuminating Engineering Society of North America (IESNA), International Electrotechniques Commission (IEC) and Underwriters Laboratories (UL).

The first milestone of the of group is to develop common terminology and key metrics presented in a consistent, user-friendly form that can be readily adopted by municipal, government and commercial customers and specifiers. A white paper on this topic, “Solar Lighting Recommended Practices: System Sizing – Preliminary Version” is scheduled for release on June 15, 2011. An introductory flyer about the Consortium and its mission will be available during the 2011 LightFair in Philadelphia, PA on May 17-19, 2011 at the booths of the respective members as well as through their corporate websites. The founding members invite other North American solar powered lighting manufacturers who are able to commit time and resources to join them in establishing a formal organization to pursue the CSL’s mission.

To inquire about participation in the CSL please contact