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.

Code change will reduce hot water waste, save Americans time and money

iapmoPlumbing inspectors, manufacturers, engineers, contractors, labor representatives and other industry technical experts voted overwhelmingly recently to make a change to plumbing codes that will ensure hot water pipes in new homes and commercial buildings are insulated. Overall, insulation of hot water pipes will shorten the amount of time spent waiting for hot water at showers and faucets, and cut hot water waste by 15 to 30 percent.

The vote took place during the review of proposed changes to the International Association of Plumbing and Mechanical Officials (IAPMO) Uniform Plumbing Code. The proposal was championed by the United Association of Journeymen and Apprentices of the Plumbing and Pipefitting Industry and the Natural Resources Defense Council.

The change stipulates that hot water pipes be insulated for all homes and commercial buildings built after 2015. Since more than a quarter of all hot water draws occur within an hour of each other, insulation can help water sitting in pipes retain its heat long enough for the next use.

A recent modeling study by the National Renewable Energy Laboratory estimated that more than 10 percent of all the hot water drawn for showering in a typical single-family home is not hot enough to use. Americans take more than 200 million showers a day. Using EPA estimates of the amount of water drawn while showering, about 280 million gallons of hot water is being discarded without use every day nationwide – an amount equal to all the water sold on an average day last year by the Las Vegas Valley Water District. This is water that has been heated by a water heater, drawn into a hot water pipe, and then left cooling down in the pipe to a point where it is not hot enough to use the next time hot water is needed. Too often, these hot water pipes are uninsulated, making the cool-down more rapid and more complete.

By incorporating this proposal into the next edition of the International Association of Plumbing and Mechanical Officials’ model plumbing code, officials bring this change to communities in Nevada, California, Idaho, New Mexico, North Dakota and jurisdictions around the country that use IAPMO’s Uniform Plumbing Code as the model for their own local codes.

E-book version of NBIMS-US available for $5

Natl Inst of Building ScienceThe National Institute of Building Sciences buildingSMART alliance has officially released the e-book version of the National BIM Standard-United States® (NBIMS-US™) Version 2 (V2), the first-ever consensus-based standard governing building information modeling (BIM) for use in the United States. It was first released in spring 2012 as a free, online standard. With this new release as an eBook, the Alliance helps the NBIMS-US V2 advance the art and science of the building life cycle by making the standard that much easier to reference anywhere, anytime.

Developed in response to requests for an off-line and portable form of the standard, the eBook contains the fixed content of the NBIMS-US™ V2, as well as internet-accessible links to reference supporting material online. NBIMS-US™ V2 covers the full life cycle of buildings—from planning, design and construction to operations and sustainment. Part of an international effort, the standard is serving as the kick-off point for a number of other countries around the world to adopt as their own BIM standard, as well as the basis of NBIMS-US™  V3, which is currently under development here in the United States.

The standard is arranged into three main categories: reference standards, information exchange standards (which are built upon the reference standards) and best practice guidelines that support users in their implementation of open BIM standards-based deliverables.

The Alliance, which is both a council of the Institute and the North American chapter of buildingSMART® International, is working with several other nations on BIM standard development. The United Kingdom, Ireland, Canada, Korea, Australia and New Zealand are all using the NBIMS-US™ V2 as the basis for their own standards. The NBIMS-US™ V2 eBook is compatible with MAC and PC devices, Android Tablets, Kindle and Nook eReaders, and related formats. The application is available online through the Institute Store for just $4.99. Download the NBIMS-US™ V2 eBook now.

Subscriptions to ASTM building standards now available

ASTM LogoASTM’s Standards for Sustainability in Building, is an online collection of standards that covers almost any green rating system or code that users may come across in the marketplace. It provides instant access to 202 ASTM standards that address sustainability or aspects of sustainability relative to buildings and construction.

This revised collection now includes the LEED system, the most globally common green building system, and ASHRAE 189.1, the alternate to the IgCC. It also features all of the ASTM standards referenced by the latest editions or versions of the Federal Green Construction Guide for Specifiers, the International Green Construction Code (IgCC) and Green Globes®.

ASTM Standards for Sustainability in Building is available as a one-year online subscription for $340 USD (searchable stock # SUSTAINBLDG). Subscriptions include access to redlines, withdrawn and historical standards.

To purchase ASTM publications, search by stock number on the ASTM Web site (, or contact ASTM Customer Relations (phone: 877-909-ASTM;

NIBS report highlights four areas in need of improvement

Natl Inst of Building ScienceA new report by the National Institute of Building Sciences Consultative Council highlights four areas where the industry and the nation need to focus their efforts in order to improve buildings and infrastructure. A summary of the report, “Moving Forward: Findings and Recommendations from the Consultative Council,” appears in the Institute’s 2011 Annual Report to the President of the United States. This year’s priorities include: Defining High-Performance and Common Metrics; Codes and Standards Adoption and Enforcement; Energy and Water Efficiency; and Sustainability.

While the building community faced numerous challenges tied to the economy and employment in 2011, representatives of leading organizations came together to identify a path forward. The resulting report developed by the Consultative Council recommends that:

  • The building community should work to define metrics for achieving high-performance buildings—including both qualitative and quantitative measures.
  • The National Institute of Standards and Technology, the U.S. Department of Energy, the Institute and others should encourage cities and smaller communities to adopt and enforce updated model codes.
  • Regulators and the building industry should support efforts by codes and standards developers and adopting jurisdictions to format criteria in ways that simplifies and enhances the ability to verify compliance.
  • Software developers, regulators and building professionals should support the development of building information modeling (BIM ) for use as an automated code-checking tool that can improve compliance and streamline the approval process.
  • The U.S. Government should develop incentives for state and local governments to require water metering of all buildings and to adopt and enforce comprehensive “green” building or plumbing codes.
  • The U.S. Government should provide a tax incentive for building owners who voluntarily get their buildings audited and that implement the recommendations to reduce energy and water use.
  • Policy makers and members of the building community are encouraged to use a common definition for sustainability.
  • The building community needs mechanisms (e.g., budgets, insurance and tax incentives) to help finance sustainable life-cycle performance for buildings and related infrastructure.

Consultative Council members that contributed to the 2011 report include: ASTM International; American Institute of Architects; American Society of Civil Engineers; ASHRAE; Associated General Contractors of America; Building Owners and Managers Association, International; Construction Specifications Institute; ESCO Group; Extruded Polystyrene Foam Association; Glass Association of North America; Green Mechanical Council; HOK; Illuminating Engineering Society; International Association of Lighting Designers; International Association of Plumbing and Mechanical Officials; International Code Council; Laborers’ International Union of North America; National Insulation Association; NORC at the University of Chicago, and United Association of Journeymen and Apprentices of the Plumbing and Pipefitting Industry.

Download the Institute’s Annual Report to the President of the United States, which includes a summary of the Consultative Council report. Download the full Consultative Council report.

Guide establishes framework for implementing COBie into building projects

Natl Inst of Building ScienceThe National Institute of Building Sciences buildingSMART alliance™ (bSa) is calling for public comment on a draft guide that establishes the framework for implementing the Construction Operations Building information exchange (COBie) standard.

As with any contract deliverable, information deliverables require specifications to set the expectations of quality that need to be met. All bSa information exchange standards are specifically designed to be contractible standards for use with building information models (BIMs). One of the first bSa information exchange standards to be included in the National BIM Standard-United States™ (NBIMS-US™), COBie identifies the minimum requirements for what digital data should be collected during design and construction so that the information is available later to manage assets throughout the life of the building.

Providing owners with a minimum national standard for capturing, updating and exchanging asset information digitally is the first step to ensuring such information is delivered by the project team. The COBie Guide sets the framework for project owners and teams to develop a practical COBie implementation strategy. Once a given owner customizes the document to meet the needs of the project, that owner’s version of the Guide becomes the reference point for the project team’s design and construction specifications. For those owners who have not previously required COBie, the basic COBie standard can be used without customization.

The basic COBie standard requires all scheduled or tagged equipment to be identified by type and location. It requires the project team to capture the make, model and serial numbers, tag, installation date, warranty and scheduled maintenance requirements (which reflects current practice in most construction contracts).

The COBie Guide results from years of developing and pilot testing the standard. Beginning July 2, the Guide will be available for a three-month review by interested buildingSMART alliance members and then updated based on consensus feedback. Once finalized, The COBie Guidewill be submitted as a “best practice” ballot to NBIMS Version 3.

The comment period closes Tuesday, October 2. Download the COBie Guide and provide comments.

About the National Institute of Building Sciences
The National Institute of Building Sciences, authorized by public law 93-383 in 1974, is a nonprofit, nongovernmental organization that brings together representatives of government, the professions, industry, labor and consumer interests to identify and resolve building process and facility performance problems. The Institute serves as an authoritative source of advice for both the private and public sectors with respect to the use of building science and technology.