HIGH-PERFORMANCE DAYLIGHTING daylight aperture optimization for the Southface Eco Office by Jim Nicolow, AIA LEED accredited professional Download full article in pdf format

Throughout the majority of human history, natural forces have directly shaped our structures. A keen awareness of natural light, and the purposeful introduction of natural light into our buildings, had a significant impact on building form. With the relatively recent development and proliferation of technologies such as inexpensive artificial lighting and central heating and air conditioning systems, we went through a period where many of our buildings ceased to be informed by natural systems. Thankfully, the pendulum is beginning to swing in the other direction.

Southface Energy Institute, a 25-year-old, nonprofit environmental organization located in Atlanta was conceived with a focus on energy-efficient, environmentally responsible residential construction. The Institute’s innovative EarthCraft House Program, one of the country’s most successful residential green building programs, recently certified its 1,000th home. Over time, the Southface mission has expanded to include the promotion of sustainable homes, workplaces and communities through education, research, advocacy and technical assistance. With the growth in mission, the organization has also expanded, to the point that it has outgrown its existing residential demonstration building.

ECO OFFICE AT SOUTHFACE ENERGY INSTITUTE SIZE: 10,000 SQUARE FEET LOCATION: ATLANTA, GA. DESIGN TEAM OWNER: SOUTHFACE ENERGY INSTITUTE ARCHITECT: LORD, AECK & SARGENT STRUCTURAL: KSI/STRUCTURAL ENGINEERS MEP/FP: KEEN ENGINEERING CIVIL: EBERLY & ASSOCIATES LANDSCAPE: ECOS ENVIRONMENTAL DESIGN DAYLIGHTING: ENSAR GROUP CONSTRUCTION MANAGER: HARDIN CONSTRUCTION GROUP RESOURCES THE DAYLIGHTING COLLABORATIVE HTTP://WWW.DAYLIGHTING.ORG/ TIPS FOR DAYLIGHTING WITH WINDOWS HTTP://EETD.LBL.GOV/BTP/PUB/DESIGNGUIDE/ SUSTAINABLE PRODUCTS SPECIFIED MICROTURBINE BY CAPSTONE; BP PHOTOVOLTAIC PANELS BY BP GASOLINE RETAIL OPERATIONS IN ATLANTA; GREEN ROOF BY SOPREMA; CONTROLS, FIRE ALARM AND SECURITY SYSTEM BY JOHNSON CONTROLS; ADDITIONAL SUPPORT PROVIDED BY THE NATIONAL RENEWABLE ENERGY LAB, THE GEORGIA ENVIRONMENTAL FACILITIES AUTHORITY AND ROOFCHEK INC.

In order to meet the needs of an expanding program, while providing a dynamic, high-performance commercial demonstration building, Southface Energy Institute commissioned Lord, Aeck & Sargent Architecture to design the new Eco Office adjacent to its existing residential facility. The Eco Office will showcase commercial green building techniques including energy efficiency and solar design, efficient water use/reuse, smart selection of materials/resources, environmentally friendly construction practices, extensive daylighting, and appropriate waste management. As the residential demonstration building helped launch the EarthCraft House program to penetrate the green residential market, Southface expects the new office to transform the market for commercial green building.

“The 10,000-square-foot Eco Office will demonstrate the added value to the property owner and improved occupant productivity,” said Jules Paulk, director of Southface Green Building Services. “A green building demonstration of this size is particularly relevant to the marketplace, as 70 percent of U.S. commercial buildings are less than 20,000 square-feet."

SUSTAINABLE DESIGN PHILOSOPHY

Aside from their thorough knowledge of high-performance building strategies, Southface brought the “state of the shelf” concept to the project. While the Eco Office will include cutting-edge technologies, such as combined heat and power generation via a Capstone Microturbine and a desiccant dehumidification system, the overriding goal was the creation of a facility that demonstrates the benefits of optimized, integrated design. The Eco Office will illustrate the significant energy efficiency benefits achievable through the thoughtful design, selection and assembly of a conventional kit of building parts (i.e., windows, walls, lighting, etc.), rather than focusing on expensive, add-on technologies. “I want developers and building owners to tour the new facility and say, ‘I can do this,’” said Dennis Creech, Southface Energy Institute’s executive director.

THE CASE FOR DAYLIGHTING

Daylighting—the use of sunlight to illuminate building interiors—is consistent with one of the key tenets of sustainable design: make optimal use of the resources already present before resorting to creating them through artificial means. Daylight harvesting involves using naturally available sunlight to offset artificial lighting use and its associated energy consumption and cooling loads. Properly designed daylighting provides benefits in three broad categories: energy, productivity and the environment.

ENERGY

For commercial buildings, artificial lighting, and its associated cooling energy, represent 30 percent to 40 percent of total energy usei. The availability of daylight corresponds nicely with hours of operation of a typical commercial office building, and the potentials for peak shaving due to reduced lighting and cooling loads are significant. The association of daylighting with reduced cooling loads may seem counter-intuitive at first, given the common use of direct sunlight for passive solar heating. However, filtered sunlight is a cooler lighting source than artificial lighting, having over twice the luminous efficacy of fluorescent lighting. To avoid a cooling penalty for the use of daylight, it is critical to tune the building’s facade to avoid direct solar gains when the building is in cooling mode.

PRODUCTIVITY

Assuming a 20-year lifecycle, the cost of owning and operating an office building breaks down roughly into three categories: 3 percent for financing and construction, 3 percent for maintenance and energy, and 94 percent for payroll for the building’s occupantsii. As these data suggest, the savings from even a modest improvement in employee productivity will eclipse the commercial office building’s energy energy costs over its lifecycle. Studies have shown a range of productivity and performance benefits associated with daylighting and the provision of views, including increased speed, improved mental function and memory recalliii; improved learningiv, reduced absenteeismv, and increased salesvi. Increasing knowledge of daylighting’s benefits to productivity and satisfaction should also lead to higher lease rates for daylit facilities and improved tenant retention.

ENVIRONMENT

Daylighting, and the resulting reduction in energy required for artificial lighting and cooling, reduces the adverse environmental impacts associated with power generation. In Georgia, where well over half of the electricity is generated in coal-fired power plants, reduced demand for electricity translates directly to cleaner air and reduced greenhouse gas emissions. With cooling of thermoelectric power plants accounting for over half of the water use in Georgia, reduced demand for electricity also translates directly to reduced water use.vii

DAYLIGHTING DESIGN PROCESS

In their seminal work “Daylighting,” Hopkinson, Petherbridge and Longmore identify two critical aspects of daylighting: “The first is to provide sufficient illumination for work to be done efficiently, quickly and without error. The second is to provide a pleasant visual environment.” In essence, it is critical to provide enough light at a relatively uniform illumination. In the context of sustainable design, there is a third critical aspect of daylighting: the control of solar gains. Aside from the risk of glare, direct solar gains can cause significant cooling loads if introduced when the building is in the cooling mode.

The following sections describe the process by which the building was configured, and specifically how the south facade was designed and optimized.

SPATIAL CONFIGURATION

For access to daylighting from windows, occupied spaces that can benefit from daylight should be located toward the exterior of the building. Sunlight is easiest to control on the north and south facades, and more difficult to control on the east and west. The majority of solar gain in the summer falls on the east and west facades and on the roof, while the majority of solar gain in the winter falls on the south façade. The Eco Office was configured to maximize daylighting from the north and south, with only limited view windows on the east and west. The routinely occupied spaces were located to the north and south to maximize access to daylighting, with open office area to the south and the private office and conference room to the north. The intermittently occupied restrooms and workroom were located toward the core of the building, where daylight access is more limited.

PASSIVE SOLAR, OR DAYLIGHTING

In evaluating the potential benefits for daylighting, and balancing the potential opportunities or penalties for passive solar heating, the first step is to determine when the building will require supplemental heating and when it will be in a neutral mode or cooling mode. For small, envelope-dominated buildings, this can be determined simply by analyzing the typical outdoor temperatures. Large, internal-load dominated buildings may never require supplemental heating, particularly when the perimeter zones are enclosed by a high-performance thermal envelope. Many commercial projects, however, will fall somewhere in between. In most cases, it is beneficial to perform preliminary thermal modeling to determine the part of the season, if any, when the building will be in the heating mode and can benefit from controlled solar gain. This information can then be used to ‘tune’ the facade elements to allow solar gain only when beneficial. For the Eco Office, solar gain was desirable from roughly the end of September through March.

SOLAR GEOMETRY

After identifying the periods during which solar gain would be desirable, the design team next investigated the path of sunlight into the building. For a given locale, the precise location of the sun at any given time can be calculated. The University of Oregon has a useful online program that will quickly generate Sunpath Diagrams for a given zip code (http://solardat.uoregon.edu/SunChartProgram. html). In Atlanta, using the end of September as the cutoff for the cooling season as outlined above, the Sunpath Diagram illustrates that at solar noon on September 21, the solar elevation will be approximately 56 degrees above horizontal (solar gain angle). Another useful angle is the elevation of the sun on its lowest arc, December 21. At the low, winter angles, the sun is more likely to pose direct glare problems for south-facing windows. In Atlanta, this is approximately 32 degrees at solar noon (winter glare angle).

DAYLIGHTING SECTION

For a side-lit space with south facing windows, a general rule-of-thumb for daylight penetration is about one-and-a-half-times the head height for standard windows up to over two-times the head height when a light shelf is employed. And, in general, the higher the window is placed, the deeper the resulting daylight penetration.

To maximize the penetration of daylight, the ceiling was sloped upward toward the windows, allowing maximum window height. A light shelf—a horizontal element above eye level designed to improve luminance distribution —was also used to further increase daylight penetration, provide more uniform illumination, control glare, and shade the glazing below. The majority of the daylighting will come from the glazing above the light shelf, the daylight glazing. This glazing is relatively transparent (Tvis, or visible transmittance, is typically in the range of 50 percent or higher). The overhang above is sized to prevent solar gain through the daylight glazing during the cooling season, and the interior light shelf is sized to prevent direct glare in the winter.

The glazing below the light shelf, the vision glazing, provides some daylighting, but its primary mission is providing views and connection to the exterior for the occupants of the space (Tvis often as low as 20 percent to 40 percent). The exterior light shelf above controls solar gain, and winter glare is controlled via a “bottom up” operable shade.

To test the performance of the façade design over time, based upon the ‘static’ solar geometry analysis assumptions, a three dimensional model of the building was created and analyzed dynamically with MicroStation V-8 by Bentley Systems. Renderings were run for different times of the year, dawn to dusk, to evaluate the changing solar penetration over time. As illustrated in the diagrams, the direct solar gain is effectively blocked through the end of September from morning through afternoon. By contrast, in December when solar gain is desirable, there is significant solar gain. The interior light shelf effectively blocks glare from the upper daylight glazing and shades can control glare from the lower vision glazing.

LIGHT LEVELS

When designing a daylit space, is often desirable to exceed recommended light levels for artificial illumination by several times in order to maximize the time that light levels provided by daylight are above the lowest thresholds. The key is providing uniform illumination to prevent glare, as the eye can readily adapt to higher lighting levels if they are uniform. The brightness of interior finishes will significantly impact the light levels in a space, with more reflective surfaces helping to bounce more light, providing higher light levels and more uniform illumination. Recommended reflectance levels for daylit spaces are a minimum of 80 percent for ceilings, 50 percent to 70 percent for walls, and 20 percent to 40 percent for floors.viii

The design team also analyzed expected lighting levels with LumenMicro V2000, by Lighting Technologies, Inc. The program can generate renderings for various times of day and season, and foot-candle contour maps identifying the actual light levels predicted.

For the proposed design, maximum daylight levels are expected to fall in the 300- 400 foot-candle range. As shown in the diagram, the levels are fairly uniform throughout the space.

LumenMicro can also be used in combination with thermal modeling to optimize the balance between the amount of glazing necessary for effective daylighting against the potential thermal penalty of glazing versus opaque walls.

SUMMARY

Given the array of energy, productivity and environmental benefits provided by daylighting, it is a sustainable design strategy particularly well suited to commercial projects. Daylighting must be considered early in design, as its successful integration may significantly impact the building’s form. Successful daylighting must provide sufficient light and uniform illumination while preventing unwanted solar gains. The first step in effective daylighting is the design and optimization of the building section and façade.

Software tools can facilitate a quantitative, accurate approach to daylighting design. Subsequent steps include the integration of artificial lighting and lighting controls to facilitate daylight harvesting, and the selection of appropriate furnishings and finishes. Although this process involves a full range of modern tools and technologies, it allows nature to once again inform and shape our structures. Whether evolution or revolution, it’s a welcome change.

Jim Nicolow, AIA, is a LEED Accredited Professional and sustainable design specialist for Lord, Aeck & Sargent Architecture (www.lordaecksargent. com), Atlanta, and can be reached at jnicolow@ lasarchitect.com. Lord, Aeck & Sargent is a full-service architectural firm specializing in science, historic preservation and education. The firm works to promote buildings that are environmentally responsible, profitable, and healthy places to live and work.

FOOTNOTES

i O’Connor, J. et al, Tips for Daylighting with Windows, the Integrated Approach, Ernest Orlando Lawrence Berkeley National Labs, LBNL-39945

ii Temoey, S.E., et al, The Design of Energy Responsive Commercial Buildings, John Wiley & Sons, 1985

iii Heschong Mahone Group, Windows and Offices: A Study of Office Worker Performance and Indoor Environment, California Energy Commission, 2003

iv Heschong Mahone Group, Daylighting in Schools. An investigation into the relationship between daylight and human performance, California Board for Energy Efficiency, 1999

v Romm, J and Browning, W, Greening the Building and the Bottom Line, Increasing Productivity Through Energy- Efficient Design, Rocky Mountain Institute, 1994

vi Romm, J and Browning, W, et al vii Fanning, J, Water Use in Georgia, 2000; and Trends 1950-2000, Proceedings of the 2003 Georgia Water Resources Conference, 2003

viiiO’Connor, J, et al

ix O’Connor, J. et al, Tips for Daylighting with Windows, the Integrated Approach, Ernest Orlando Lawrence Berkeley National Labs, LBNL-39945

x Temoey, S.E., et al, The Design of Energy Responsive Commercial Buildings, John Wiley & Sons, 1985

xi Heschong Mahone Group, Windows and Offices: A Study of Office Worker Performance and Indoor Environment, California Energy Commission, 2003

xii Heschong Mahone Group, Daylighting in Schools. An investigation into the relationship between daylight and human performance, California Board for Energy Efficiency, 1999

xiiiRomm, J and Browning, W, Greening the Building and the Bottom Line, Increasing Productivity Through Energy- Efficient Design, Rocky Mountain Institute, 1994 xivRomm, J and Browning, W, et al

xv Fanning, J, Water Use in Georgia, 2000; and Trends 1950-2000, Proceedings of the 2003 Georgia Water Resources Conference, 2003

xviO’Connor, J, et al