Guide to Mechanical / electrical equipment for buildings: PART III: ILLUMINATION: Daylighting Design

DESIGNING WITH DAYLIGHT IS BOTH AN art and A science. The designer, in concert with the appropriate combination of building geometries, materials, and light produced by site conditions, can produce health and well-being, visual delight (FIG. 1), and intended ambience-and reduce dependency on electrical energy use. Studies have demonstrated that daylighting improves indoor environmental quality for occupants. Daylighting design is often mistakenly understood to mean that an abundance of light should fill a space; successful design, however, involves a careful balance and control of heat gain and loss. A variety of strategies are avail able to control and enhance daylight through shading devices, lightshelves, glazing, atria, courtyards, and material finishes (both interior and exterior). Daylighting is an easily achievable LEED strategy if a building can provide a minimum daylight factor of roughly 2% in 75% of all occupied spaces.

FIG. 1 Visually appealing daylighting elements at (a) Chiswick Park Office Complex, London, UK. (b) Hong Kong International Airport, Hong Kong, China.

1. THE DAYLIGHTING OPPORTUNITY

(a) Importance of Daylighting Design

Historically, the architectural form of buildings, placement of windows, and location of rooms were guided by the availability of daylight as the primary source of illumination. Daylight was the only source of abundant light for buildings, pro vided through deep windows and thick walls and perhaps replaced (although inadequately) in the evening by the flicker of a candle flame or an oil lamp. Building form changed dramatically with the development of fluorescent lighting technologies, allowing interiors to be uniformly lit by electric lighting systems and to function at cooler temperatures (as opposed to the higher temperatures produced by heat-intensive incandescent lamps). Designing with daylight can improve energy efficiency by minimizing the use of electricity for lighting as well as reducing associated heating and cooling loads. Daylighting is a critical design factor to those concerned about global warming, carbon emissions, and sustainable design-in addition to visual comfort.

Research has found daylight to be an important factor influencing human behavior, health, and productivity. Windows admitting daylight provide occupants with a view and a temporal connection with the outdoors. Daylight renders the environment in a vivid range of experiences and delight. It is important for basic visual requirements to view tasks and to perceive space. How daylight is delivered is in the hands of the designer at the beginning stages of design. The option of ignoring daylight in our high-energy-cost and rapidly-diminishing-natural-resources world is no longer available. This Section describes daylight strategies to increase occupant satisfaction, control glare, provide appropriate vertical and horizontal illumination, and address the potential for energy savings to enable the designer to create a proper visual environment.

(b) Planning for Daylight throughout Design

Designing buildings for daylighting is a complex systems integration process. Daylighting design begins with situating a building on its site and continues through each phase of design; making the best use of daylight continues throughout a building's occupancy. While overall design goals remain generally fixed throughout each design phase, there are key concerns associated with each of the phases.

For example, in the conceptual design phase, building form, orientation, layout, and major apertures might be primary elements. Further into design development, there would be specification of materials and interior finishes, and zoning for integration with electric lighting and other services; control systems would be coordinated with occupancy schedules, and commissioning test procedures set in place.

During occupancy, fine-tuning and maintenance of the system would occur, and a post-occupancy evaluation performed to determine satisfaction, visual comfort, and lighting system performance.

(c) Energy Savings with Daylighting

To obtain lighting energy savings in a building, six "essential" ingredients for daylighting design are recommended by the Illuminating Engineering Society of North America (IESNA) in RP-5-99, Recommended Practice of Daylighting:

1. Plan interior space for access to daylight.

2. Minimize sunlight in the vicinity of critical visual tasks.

3. Design spaces to minimize glare.

4. Zone electric lighting for daylight-responsive control.

5. Provide for daylight-responsive control of electric lighting.

6. Provide for commissioning and maintenance of any automatic controls.

Energy savings from reduced electric lighting will be compromised if any of these factors are overlooked.

If any one of the first three is missing, daylight will make little contribution to the illumination of the space. Each of these factors is discussed in this Section.

(d) Goals of Daylighting

Improved aesthetics, provision of human biological needs (circadian rhythms and visual relief), and reduction of electric lighting energy usage are the most important advantages of daylighting a building. Key goals in daylighting design are to provide sufficient illuminance, minimize the perception of glare, and provide for overall visual comfort.

2. HUMAN FACTORS IN DAYLIGHTING DESIGN

The following human-related factors (as opposed to the physical aspects of light) are described briefly to illustrate the importance of considering daylighting, and especially these factors, in the design of spaces.

(a) Windows and View There is a common belief that if a window is placed in a wall, there will be sufficient view and daylight.

The view function of a window, however, is very different from the daylighting function. The most preferred views from a window include the sky, the horizon, and the ground. In offices, people enjoy having windows in their work space because of the views. The functional advantage is that people can look into the distance to reduce eye fatigue after doing close desk tasks. Depending upon the type of facility, the designer should be aware of special circumstances--for example, ensuring that bedridden occupants of care facilities can have a view from their vantage point, providing lower sills in facilities for children (depending upon safety), or accommodating people in wheelchairs by providing low-sill windows in bedrooms and other areas.

(b) Productivity and Satisfaction

Productivity is a complex issue that is difficult to isolate or attribute to a single parameter such as day lighting. The connection to the temporal qualities of daylight improves our psychological well-being and productivity. In studies of classrooms, windows, daylight, and performance, researchers found that students with more daylighting in their classrooms progressed faster on math and reading tests than students with less daylighting. Also, sources of glare negatively impact student learning, and the issues of control of windows, blinds, sun penetration, and acoustic conditions are important for teachers. In another study, retail stores were found to have a "daylight effect on increased monthly sales".

(c) Controlling Daylight in Interior Spaces

Daylight, whether diffuse light or direct sunlight, provides significant benefits associated with psychological well-being. On the other hand, there are potential problems-such as glare or substantial cooling loads-caused by uncontrolled quantities and qualities of light. Direct sunlight is not, how ever, always a liability. In non-task areas, a momentary sunny patch, a streak of sunlight against a wall, or a series of multiple shapes provides visual interest and dynamism to a space. Sunlight in task areas can be controlled in a number of ways:

• Provide exterior fixed shades that exclude sun light for all sun positions.

• Use systems that diffuse the incident sunlight sufficiently to eliminate glare potential.

• Provide occupant-controlled adjustable shades.

(d) Minimize Glare

Glare is a difficult problem to overcome when balancing daylight and view. Any window (including north exposures) can produce problematic glare if the window is within the field of view. High contrast ratios between a window and adjacent surfaces can occur unless the window is designed to reduce luminance ratios through the use of sunshading devices, lightshelves, high-reflectance interior surfaces, light-colored window surrounds and mullions, and low-transmittance glazing (though such glazing will reduce light flux through the window). Furniture should be oriented to work with side lighting (as opposed to having an occupant face a window).

3. SITE STRATEGIES FOR DAYLIGHTING BUILDINGS

Optimal daylighting opportunities depend upon a building's position on a site relative to available daylight, horizon obstructions, orientation, and building form. The quality of daylight, its effects on illumination, and solar position for passive heating and control of cooling loads are of particular importance to the designer. Site obstructions such as neighboring buildings, trees, and landforms will determine the maximum available daylight on a site and the maximum project envelope that will preserve daylight access to adjacent properties (FIG. 2).

Orientation. In many locations, an ideal orientation for buildings is an elongated, narrow plan allowing the north and south façades of the building maximum exposure to more easily controllable daylight. From a daylighting standpoint, this is desirable because direct solar radiation received by the south façade is easier to control to prevent excess solar gain, is relatively uniform, and is necessary for passive solar heating strategies. The nearly constant diffuse skylight availability on the north façade is advantageous for uniform and soft day lighting. Figure 14.3 shows how orientation affects cooling, lighting, and heating energy for a building.

Form. Establishing an appropriate building form in the early stages of design is critical to day lighting performance. The width of the long, narrow plan previously described will determine how much of the floor area will have access to usable daylight. Generally, a 15-ft (4.5-m) perimeter zone can be completely daylit, a 15- to 30-ft (4.5- to 9.0-m) area can be partially daylit, and an electrically lit area beyond 30 ft (9 m) can be used to determine the width of a building.

FIG. 2 Protecting a site from obstructions to daylight.

FIG. 3 Effect of building orientation on energy consumption.

FIG. 4 (a) Plan diagrams of unilateral and bilateral daylighting. (b) Windows on two sides (a bilateral approach) at the Crystal Cathedral campus, Anaheim, California.

FIG. 5 (a) With higher windows, daylight extends farther into a space. (b) High windows in a classroom at the University of Oregon.

FIG. 6 (a) Windows adjacent to a wall provide an additional reflecting surface. (b) Reading carrel adjacent to a window at the Graduate Theological Union Library, Berkeley, California.

4. APERTURE STRATEGIES: SIDELIGHTING

Sidelighting systems admit light from apertures in window walls, and light sweeps across the space from one or more sides. The distance to which usable daylight penetrates a space and falls onto a work plane is the variable that designers work with to pro vide for sufficient illuminance. Generally, sidelighting is best for desk tasks because there are no veiling reflections, provided there is proper orientation of the worker. A number of generalized sidelighting strategies provide greater illuminance farther into a space and improve visual comfort. The variety of approaches and components available to the designer is extensive. A complete discussion is provided in Daylight in Buildings, A Source Book on Daylighting Systems and Components (International Energy Agency, 2000). Schematic examples of a few typical design strategies are described below and in Figs. 4 to 11.

• Design for bilateral lighting. Daylight within a space is generally most evenly distributed when a space is lit from two walls (bilateral lighting), as shown in FIG. 4. Bilateral lighting from "opposite" walls produces the most evenly distributed lighting condition. Unilateral lighting (windows on one wall) can increase the potential for glare.

• Place windows high on a wall. In general, for a given window area, daylight will penetrate farther into a space and have more uniform distribution when windows are placed high on a window wall (FIG. 5). If possible, raise the ceiling height to accommodate a higher window position. Use the ceiling as a reflecting surface by placing window heads as close as possible to the ceiling.

• Use adjacent walls as reflectors. Interior walls become reflectors when windows are placed adjacent to them, thus reducing the contrasting edge around the window (FIG. 6). This arrangement can also bring visual delight if the reflecting wall is a light color, which will reveal patterns and colors from sunlight and reflect dif fuse light farther into the space.

• Splay the walls of an aperture. This strategy is similar to the reflector strategy described previously, where light washes across a longer or rounded surface area around the window. When the edges of window openings are splayed (FIG. 7) or rounded, these illuminated surfaces surrounding the window reduce contrast and are more visually comfortable, and therefore reduce the potential for glare.

• Provide daylight filters. Daylight may be modified (either blocked or diffused) by a number of elements, which include trees, vines, and trellises (FIG. 8) on the exterior of a building; filters for the interior of a building may include blinds, drapes, or translucent glazing.

• Provide summer shading. Depending upon passive solar heating and cooling design strategies, in many instances direct sunlight should be blocked before it enters a space at certain times of the year.

Figures 9 to 11 show examples of exterior louvers (horizontal or vertical), overhangs, trellises, trees, and lightshelves that can block direct sunlight, reflect diffused sunlight into a space, and provide solar control. Light-colored materials or finishes on these components will reduce contrast between the element and the view or sky beyond. Lightshelves that also serve as a shading device can be designed as a horizontal (integrated or attached) component positioned inside and/or outside a window. Typically above eye level, they divide a window into a lower view portion and an upper area exclusively for daylight.

FIG. 7 (a) Splayed window provides additional reflecting surfaces. (b) Deeply set window within a thick wall of a room in a medieval village in Il Borro, Italy.

FIG. 9 (a) Horizontal overhangs block light but also act as a reflector for light from the ground plane. (b) Horizontal shading devices at Ash Creek Intermediate School, Monmouth, Oregon.

FIG. 8 Filters. (a) Trellis at Westcave Environmental Center, Round Mountain, Texas. (b) Several layers (trees, shading, curtains) of a window can filter light and shade a window.

FIG. 10 (a) Lightshelf reduces the daylight factor near a window and increases it at greater depths. Shelf material (opaque, translucent) and angle of installation (horizontal, sloped up) markedly affect performance. (b) Opaque white surface at the top of a lightshelf in the Emerald People's Utility District office building, Eugene, Oregon.

5. APERTURE STRATEGIES: TOPLIGHTING

FIG. 11 Fixed horizontal louvers on the south façade at the Phoenix Public Library, Phoenix, Arizona.

Skylights, roof monitors, and clerestories are suit able aperture strategies for the top floor of a building, particularly for interior locations of large floors that are far from perimeter windows. To prevent veiling reflections or direct glare situations, top lighting components should be placed away from the offending zone (areas with a direct view from an occupant), or a baffle or interior reflector should be used to diffuse and control daylight. Most of the strategies for sidelighting also apply to top-lighting, several of which are discussed here.

• Splay the "walls" of an aperture. Splaying the sides of a skylight makes the skylight appear larger because light washes along a larger surface area and reflects diffuse light into the space (FIG. 12). This strategy reduces the potential for glare similarly to the way splayed windows function.

• Place top-lights high in the space. Higher ceilings with skylights allow more surface area for light to diffuse upon, virtually becoming a larger source (FIG. 13). This strategy works well in spaces where the skylight is well above the field of view.

• Use interior devices to block, baffle, or diffuse light.

Direct sunlight can be redirected by a reflector below a skylight, clerestory, or roof monitor that, depending upon the surface material, diffuses the light onto another surface within the space (Figs. 14 and 15).

FIG. 12 (a) Splayed surfaces of a skylight provide areas for diffusely reflected light. (b) Gallery skylight at the J. Paul Getty Museum, Los Angeles, California.

FIG. 13 (a) A skylight near a north wall provides reflecting surfaces for uniform light distribution and reduces the potential for glare. (b) One of the "bottles" of light (skylight) at St. Ignatius Chapel at Seattle University in Seattle, Washington.

FIG. 14 (a) Skylight with baffles that block direct solar radiation. (b) Baffled skylight daylighting design at Mt. Airy Public Library, Mt. Airy, North Carolina.

FIG. 15 Clerestory skylights with louvers at the U.S. Holocaust Memorial Museum in Washington, DC (Pei, Cobb, Freed & Partners, 1993).

6. SPECIALIZED DAYLIGHTING STRATEGIES

A number of innovative daylighting systems can be categorized as experimental, yet they have tremendous potential. Some of these strategies include laser-cut or prismatic panels, fiber optics, solar tubes, and heliostats. More advanced systems use reflectors and lenses to introduce concentrated luminous energy into some type of light-conducting device. These may be fiber-optic bundles, prismatic light pipes, or some type of mirrored channel. The problem of heat rejection becomes more severe as the degree of solar energy concentration increases.

Thus, light pipes are much less critical in this regard than are optical-fiber systems. The efficiency and economic feasibility of these systems are interdependent because of the materials used; the farther the light is transmitted, the lower the system's over all efficiency and the higher the cost to make the system technically feasible.

Light pipes. This term refers to several strategies: daylight pipes, electric light pipes, and fiber-optic pipes (FIG. 16). The light pipe operates by collecting light through a heliostat; channeling daylight (or electric light) through a reflective tube made of prismatic glass, plastic film, and mirrors; and diffusing light at the end of the pipe.

It is an exciting strategy because of the length it can transport light-65 ft (20 m)-from a single-point light source.

Tubular skylights. These light shafts have highly reflective surfaces and are capped by a clear sky light (FIG. 17). The amount of light transmit ted and delivered varies with the diameter of the shaft. They are convenient and economical for supplemental illumination in hallways, closets, and areas without a need for a lot of control.

The light quality is comparable to that of a ceiling-mounted fluorescent fixture (often indistinguishable).

FIG. 16 (a) Heliostat on the rooftop of a building tracks the sun and directs light into an 8-ft. (2.4-m)-wide atrium and down 14 floors. (b) Solar Light Pipe is a 120-ft. (37-m)-long, 6-ft. (1.8-m)-diameter, 12-sided steel-and-aluminum frame-enclosing laminated glass panels and surrounded by fabric-within the atrium at the Morgan Lewis building in Washington, DC.

FIG. 17 (a) Tubular skylight installation through a roof structure. (b) Top of Solatube skylights on the roof at Ash Creek Intermediate School in Monmouth, Oregon.

7. DAYLIGHT FACTOR

Daylight factor (DF) is defined as the ratio of interior illuminance (Ei ) to available outdoor illuminance DF indoor illuminance, at a given point:

(eqn. 1)

where EH is the unobstructed horizontal exterior illuminance. The daylight factor concept is applicable only where the sky luminance distribution is known or can reasonably be estimated. The Com mission Internationale de l'Eclairage (CIE) defines an overcast sky and a clear sky whose luminance distributions are fixed for the purpose of calculations. Daylight factor cannot be used with skies with constantly changing luminance (partly cloudy and direct sun) because under such conditions the daylight factor at a given point also varies continuously, making the concept useless as a calculation tool for absolute daylight values.

Daylight factor as a means of expressing interior daylight illuminance is both absolute and relative. With a given sky luminance distribution, variations in daylight illuminance inside correspond exactly to variations outside (i.e., the daylight factor remains the same). This assumes a minimal effect from obstructions and ground reflections. Thus, the daylight factor allows determination of interior daylight distribution for varying fenestration, spatial arrangement, and building orientation.

Daylight factor is constant for a given space and window configuration. Interior illuminance can easily be calculated by knowing the daylight factors for locations in a given space and the exterior illuminance derived from sky luminance data.

Daylight design analysis can use a combination of minimum exterior illuminance and corresponding minimum daylight factor requirements to predict daylight sufficiency under almost all exterior conditions.

8. COMPONENTS OF DAYLIGHT

FIG. 18 Total daylight factor (DF) is composed of the SC, ERC, and IRC. The IRC, in turn, is subdivided into reflected sky light and reflected ground light components. Note that surfaces deep in the room are illuminated with re-reflected light.

The general characteristics of daylight as a source of light (versus electric lamps) were discussed in Section 11. Understanding the components of day light is important to the design of apertures and the selection of materials. Daylight in a building consists of three components (see FIG. 18):

1. Sky component (SC)

2. Externally reflected component (ERC)

3. Internally reflected components (IRC1 + IRC2)

DF is the sum of these three components, each calculated individually for each location being considered. DF is a ratio, but the value of a given DF is based upon contributions from these components: DF = SC + ERC + IRC.

The sky component (SC) is that portion of total daylight illuminance at a point received directly from the area of the sky visible through an aperture.

As the SC represents received light, it takes into account reductions due to window obstructions (mullions, etc.) and losses in transmission; that is, SC = incident skylight - window losses The externally reflected component (ERC) represents light reflected from exterior obstructions onto the point under consideration. This does not include ground-reflected light. ERC is of significance only in built-up areas (where there are structures opposite an aperture) and can be estimated as the portion of the SC for that area of obstructed sky, reduced by the percentage of the sky obstructed (RD) and the reflectance factor (RF) of the obstruction; that is,

ERC = SC × RD × RF

Thus, if 25% of the sky is obstructed by a building with a 20% RF, we have

ERC = SC × 0.25 × 0.20

For this particular example, then ERC = 5% of SC to be added to the remaining 75% of SC (25% of the sky was obstructed).

The internally reflected component (IRC) represents the light received at the point under consideration that has been reflected from interior surfaces.

IRC is subdivided into reflected skylight (IRC1) and reflected ground light (IRC2). IRC2 is generally small, and IRC ? IRC1. IRC is, therefore, primarily dependent upon interior surface reflectances and upon the amount of window glazing, and becomes a large portion of DF deep within an interior space (see TABLE 1 for wall reflectance factors and FIG. 19 illustrating IRC as a function of the amount of glazing). IRC is normally calculated using published inter-reflectance tables, as direct calculation is extremely complex.

Typical curves for both horizontal and vertical daylight factors for a room with single (unilateral) sidelighting (windows on one side) are shown in FIG. 20. These curves are produced by a long hand daylight-protractor-aided technique (Building Research Station, London). Any change in parameters, such as window dimensions or height above the working plane, ceiling height, surface reflectance, ground reflection, and obstructions, alters these curves and requires recalculation and re-plotting. Exact calculation of even a few vari ants for a space is a tedious and time-consuming procedure.

FIG. 19 Plot of the IRC of the daylight factor as a function of amount of glazing, expressed as per DF (i.e., as a percent age of exterior illuminance). As expected, the effect of a lighter wall finish becomes more pronounced as the fenestration area increases.

TABLE 1 Effect of Wall Reflectance Factor on the Proportion of IRC in the DF FIG. 20 Typical daylight factor curves for horizontal (DFH) and vertical (DFV) illuminance for a room with large windows on one side only. Note that the SC represents almost the entire DF near the window, but its proportion reduces at greater depths. There, inter-reflected light constitutes 50% of the available daylight.

The following manual methods describe alternative approaches available to save time and increase accuracy:

1. Use of simplifications, such as standard curves, tabular data, or the CIE method.

2. Use of a library of graphic light distribution plots with varying parameters.

3. Use of a less-laborious manual calculation procedure. One such technique is known commonly as the lumen method or the IES method.

4. Use of computer simulation software.

Designers may use daylight factor criteria as a starting point for daylight design, translating the DF values (such as those given in TABLE 2) into actual illuminances in footcandles (lux) and com paring the results to recommended illuminance values. As an example, consider two cities in the United States that have overcast skies for appreciable portions of the year-Columbus, Ohio (40º N latitude), and Seattle, Washington (48º N latitude). TABLE 3 compares illuminance values calculated by the DF method with those recommended by IESNA and the Chartered Institution of Building Services Engineers (CIBSE). For most of the year (with the exception of winter), day light provides all the light necessary for the tasks in TABLE 2. In this case, where the available exterior daylight is as low as 5000 to 7000 lux (465 to 650 fc), supplemental electric lighting would be required for all interior areas beyond H feet (that is, one window height from the window-see FIG. 20).

In addition to the recommendations in TABLE 2, the ratio between the minimum and average daylight factor in a space, which relates to contrast ratios, should be no less than 30%:

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The minimum daylight factor in any portion of a space should not drop below 0.5%, which is sufficient for circulation.

TABLE 2 Recommended Daylight Factors

9. GUIDELINES FOR PRELIMINARY DAYLIGHTING DESIGN

Guidelines provide the designer with a variety of broadly based rules useful during the conceptual and schematic stages of design. Based upon design experience and lighting research, these guidelines assume overcast sky conditions. During design development, they may be used as a starting point for performance analyses that include other parameters such as sky conditions, orientation, and wall color, using computer simulation software, physical models, and calculations.

(a) The 2.5H Guideline

This longstanding guideline in the lighting design field (FIG. 21) assumes that there will be sufficient work plane illuminance from a window up to a distance of 2.5 times the head height of the window above the work plane-assuming clear glazing, overcast skies, no major obstructions, and a total window width that is approximately half that of the exterior perimeter wall.

FIG. 21 Section shows the 2.5H guideline, which assumes that sufficient daylight for the desk plane will be delivered at a depth 2.5 times the height of the window above the desk plane.

FIG. 22 Plan shows the 15/30 guideline, which assumes that sufficient daylight will be delivered to the desk plane at a 15-ft (4.6-m) distance from the window wall. The 15- to 30-ft (4.6- to 9.1-m) daylight zone will need supplementary electric lighting, and the zone beyond 30 ft (9.1 m) will receive virtually no daylight.

TABLE 3 Horizontal Illuminances (EH) from Overcast Sky, at Selected Times, in Columbus, Ohio, and Seattle, Washington, Corresponding to the Recommended DF

(b) The 15/30 Guideline

This preliminary design guideline assumes that a 15-ft-wide (4.6-m) zone from a window wall (FIG. 22) can be daylit sufficiently for office tasks. The next 15-ft (4.6-m) zone can be partially daylit and supplemented with electric lighting.

Zones farther than 30 ft (9.1 m) from the window would receive very little daylight. In schematic design, these areas might ideally be allocated to circulation.

(c) The Sidelighting and Toplighting Daylight Factor Guideline

The size of windows, clerestories, or skylights may be estimated by using the simple formulas in TABLE 4, Parts A and B, which provide target daylight factor values. These design guidelines consider two factors: the height of the window in the wall and the window or skylight area compared to the floor area for each daylit space.

For an example of such a calculation, see the example previously discussed in Section 8: the two-story office building in Oregon (shown in FIG. 23c) of the Emerald People's Utility District.

Briefly, after selecting a target value of DFav = 4.0% from TABLE 2, the windows and clerestories (as skylights) were sized, using the DF guidelines for sidelighting and for the vertical monitor skylight from TABLE 4:

DF window or skylight area floor area av = 02 .

()

Applied to the entire typical bay, DFav = (0.2) (97 ft north 97 ft south 132 ft 22 2 ++ c clerestory) 1440 ft^2 = 0.45, or 4.5% slightly above the target DFav of 4.0%.

Note that in this example, DFmin from the side lighting occurs near the center of the building, at about the point (on the second floor) where the most light is available from the skylight. There fore, a relatively even daylighting distribution is expected on the upper floor. This is helped by the use of lightshelves and the T-shaped windows shown in FIG. 23. The seasonal window size question (more needed in winter, less in summer) was answered in this example by the use of deciduous vines outside the south windows. In winter and cool spring, the vines are bare of leaves. Warm weather brings leafy shade lasting well into the warm fall.

TABLE 4, Part C, shows design guidelines for buildings with an atrium that provides daylighting to surrounding offices. Because the lowest day light factor will occur in offices on the lowest floor (deepest within the atrium), the designer might find the required atrium aspect ratio first for the lowest floor and then size the atrium on that basis. This design approach would provide a higher daylight factor in all the offices higher in the atrium. The atrium aspect ratio = [(length × width)/height 2].

For a detailed discussion of the relationship of atrium size, rentable office floor area, and latitude, see DeKay (1992).

TABLE 4 Daylight Factor Design Estimates for Overcast Sky Conditions

FIG. 23 (a) Diagrammatic daylighting section of the office building for the Emerald People's Utility District near Eugene, Oregon.

Lightshelves (b) reduce the contrast between a lot of daylight near windows and too little daylight farther in. The resulting windows (on north façade) are T-shaped (c), with more glass area above the lightshelves and less glass below.

10. DESIGN ANALYSIS METHODS

Because of the variability of daylight, the designer may provide a balance of illumination to save electric energy and reduce utility costs while addressing issues of glare, direct sunlight, and heat gain. The art and science of daylighting is largely about understanding how to control the admission of daylight into buildings.

In the following sections, several interior day lighting analysis methods are described. The manual methods range from hand calculations that address only minimum, maximum, and average conditions to physical scale models where surfaces and apertures are easily changed. The manual and graphic calculation methods are inexpensive but limited to simple spatial geometries. Computer simulation programs can produce detailed and realistic presentations in three-dimensional graphical form. Software is widely available, but its use is dependent upon cost and training, and the user must understand daylighting concepts and principles in order to interpret the results and to overcome the limitations of simulation. Physical models still offer the designer an economical, realistic, and accurate alternative. Additionally, the intuitive understanding provided by scale models may increase the client's understanding of lighting phenomena.

FIG. 24 Maximum room depth that will maintain a minimum desired daylight factor is proportional to window size. Thus, for a room less than 25 ft (7.6 m) long with a 5-ft (1.5-m)-high window for 60% of the room's length, the depth cannot exceed 12 ft (3.7 m) if 2% DF is to be maintained at a point 2 ft (61 cm) from the rear wall.

(a) CIE Method

This method resulted from a search for a simple, rapid, straightforward, and reasonably accurate daylighting calculation method that would yield reliable results without the time-consuming constructions and calculations necessitated by other manual methods. After a study of considerable length and intensity, the CIE adopted and adapted a system developed in Australia by Dresler (Daylight Design Diagrams, 1963). The current CIE method was published in Daylight, 1970.

This system is based upon the daylight factor described previously as applied to the standard overcast CIE sky. Dresler developed a set of more than 100 curves covering rooms of varying proportions and fenestration. A typical curve is shown in FIG. 24. The curves relate minimum daylight factor (at a point 2 ft [0.6 m] from the wall opposite a window) to the maximum permissible room depth, for given reflectances and a standard window design, thus establishing the room's proportions.

Depth, or width, is the dimension at right angles to the window wall.

The curves imply that the number of design variables is so large and daylight itself is so variable that a simple routine method can be based only on minimal conditions for a given (selected) daylight duration. Therefore, the diagrams give the lowest level of daylight that can reliably be expected for a given percentage (percentile) of normal working hours in side lighted rooms and the average level in to plighted spaces.

Advantages of the system are:

1. Consideration of obstructions, exterior reflections, and interior reflections.

2. Applicability to a very wide range of side and top fenestration designs.

3. Establishment of required room proportions is architecturally more useful than solving for specific dimensions.

Limitations of the system are:

1. Inapplicable to clear sky and direct sun conditions.

2. Inapplicable to other than rectangular rooms.

3. Unusable with sunshading devices or high reflectance ground.

4. Results give points of minimum, twice mini mum, and four times minimum daylight only.

Other points must be interpolated or extrapolated.

5. Window proportions and position in a wall are fixed.

Overall, the system accomplishes what it intended.

The limitations listed are inherent in any quick, simplified daylight calculation technique.

The CIE system is usable in two modes:

1. Given complete architectural dimensional data, find interior illuminance.

2. Given incomplete architectural dimensional data and required interior illuminance, find maximum room depth and/or other room proportions that satisfy the illuminance requirement.

Mode 1 is simpler because it leads directly to an answer. For this reason, the designer should set the room length (window wall dimension) and percentage of fenestration of the window wall, leaving the room depth (perpendicular to window wall) as a variable. Alternatively, room length and depth may be set, with percentage of fenestration as the variable. Ceiling height is usually fixed. See FIG. 25 for sketches showing room parameters.

FIG. 25 Sketches indicating the parameters of the CIE calculation system. (a) A vertical section through a room with dimensional data relevant to this system. Note that the sill height has been selected to coincide with a working plane at 900 mm (3 ft). The height of the working plane usually varies between 760 and 910 mm (30 and 36 in.), the former being more common in North America, the latter in Europe. A lower sill contributes only ground-reflected light at the working plane. Where the window sill is significantly above the working plane (i.e., short windows high on a wall), this analysis system is inapplicable. (b) Calculation size (length) of windows with respect to overall room length.

FIG. 26 Plan and window wall elevation of the Seattle classroom calculation example using the CIE method. The three daylight contours are estimated based upon the calculated center point. They represent the levels maintained for 85% of daylight hours. Levels twice as high are maintained for 60% of the daylight hours.

FIG. 27 Minimum maintained external illuminance as a function of latitude for a given percentage of the normal working day.

FIG. 28 Basic design diagram that relates minimum daylight factor to room depth. Inasmuch as room depth is expressed in terms of window height, the curves effectively relate minimum daylight factor (2 ft [610 mm] from the back wall) to room proportion.

TABLE 5 Correction Factors to Be Used in CIE Daylight Calculations

FIG. 30 (a) Distance from the window at which the daylight factor is twice the minimum daylight factor. (b) Distance from the window at which the daylight factor is four times the minimum daylight factor.

FIG. 29 (a) Angle of obstruction a of an external object. (b) Correlation factors to account for the influence of external obstructions on the minimum daylight factor.

FIG. 31 (a) Daylight contours for each window of FIG. 26 are plotted on the floor plan of the room being studied. Numbers in parentheses are combined SC values. (b) The isolux contours of (a) are combined to form new isolux contours that represent the total SC of daylight within the room. (c) The final isolux contours are calculated, including correction factors. The numbers represent day light factors. Note the variance between these contours and the points calculated by the CIE method. The five design points calculated by the IESNA method are also shown. A comparison of the results of the three methods described indicates that on the room center line (a location where comparison of all methods is possible), agreement is within engineering accuracy (see text discussion).

In summary, the CIE method is relatively simple but provides only limited data on predicted performance. In this example, its exterior illuminance data (7250 lux from FIG. 27) seem to agree well with a measured average value of 7200 lux for Seattle. From the rough contours shown in FIG. 26, an integrated daylight and electric lighting strategy should be designed for areas farther from the window wall.

(Note: The term design illuminance as used with the CIE method differs from common lighting system design usage, where design illuminance is used to identify the criteria (benchmark) illuminance established for a space or position; initial illuminance identifies the illuminance actually provided at system startup, and maintained illuminance is the illuminance provided after some defined time period.)

(b) Graphic Daylighting Design Method (GDDM)

This method, which applies to overcast sky conditions and shows results as daylight factor (isolux) contours within a room (rather than individual daylight factors at specific points), was developed by Millet and Bedrick (1980). Its primary advantage over the CIE method is that its results are a family of daylight factor contours that are more useful to a lighting designer than is numerical output. The disadvantages of this method are that it is not readily applicable to clear-sky conditions, and it requires that a designer acquire a "library" of 200 or so patterns that cover most design situations. An outline of the method is presented here.

A computer simulation program (UWLIGHT) developed the daylight distribution patterns resulting from either sidelights or skylights. To generalize the system, windows are identified by height to width proportion (H/W), and the position of the isolux contours on the plan is determined by the ratio of the height of the sill above the work plane to the window height. The GDDM method can account for high windows, clerestories, and other designs intended to introduce daylight deep into a space-something that the CIE method cannot do because it is restricted to a sill height at the work plane.

FIG. 32 Typical isolux contour map for a window with a height-to-width ratio of 0.8 and a sill at the working plane elevation. Numbers represent the SC of daylight factors for an overcast sky condition. The bold rectangle on the left hand drawing represents the window outline projected onto the working plane. See insert.

(c) IESNA Lumen Method

IESNA developed the lumen method for calculating daylight availability (published as RP-23-89, Recommended Practice for the Lumen Method of Day light Calculations). Although inexpensive, like many manual methods it is limited in application-in this case, to rectilinear spaces with flat ceilings. A trade off between usability, learning curve, and cost, however, is often made when selecting a design method.

The calculation procedure for sidelighting is discussed in this section, as this is a more frequently encountered strategy than top lighting. The method, as fully described in RP-23-89, consists of four detailed steps. In the discussion that follows, the same notation and terms found in RP-23-89 are used except for bearing angle, which is referred to in the IESNA procedure as solar window azimuth.

The term bearing angle is commonly used in international sources.

Characteristics of the Method. The IESNA method is probably the most flexible manual technique available. It has the following major characteristics for sidelighting:

1. It takes into account reflected light from the ground and adjacent structures, as well as the reduction in sky light due to such structures.

2. It cannot accommodate direct sunlight, but conversely, it readily accommodates the shading devices normally used to block direct insolation.

3. Provision is made for various types of glazing, as well as common window controls such as horizontal and vertical blinds.

4. The principles of the zonal cavity calculation approach for interior lighting (see Section 15) are applied. The window height determines the cavities (i.e., the floor cavity extends to the windowsill height, and the ceiling cavity from the top of the window to the ceiling). The room cavity is therefore the window height.

5. The work plane is always at the sill height of the window. Where this is decidedly not the case (a difference of up to 1 ft is usually negligible), such as when a clerestory or a floor-to-ceiling window is used, work plane illuminance can be calculated by superposition. For instance, with a clerestory, subtract a work-plane-to-clere story sill height window from a work-plane-to top-of-clerestory window to obtain the desired result. A degree of inaccuracy is unavoidable in the calculation when the work plane is above the sill.

6. Cavity reflectances are fixed (FIG. 33) at 70%-50%-30% for ceiling, room, and floor cavities, respectively.

7. The system calculates only five points in a room on the window centerline. As noted with reference to the three points calculated by the CIE method, this is not normally sufficient to give a picture of the interior daylight distribution.

8. The method is usable in only one mode; that is, given location and full dimensional data, day lighting can be calculated. It cannot readily be used to determine desirable room proportions, given the other data, as can the CIE method.

FIG. 33 Standard conditions in a room for daylighting calculations: sidelighting. (IESNA, Recommended Practice for the Lumen Method of Daylight Calculations, RP-23-89.)

TABLE 6 Vertical and Horizontal Illuminance Values for Spring and Winter, Seattle, Washington

TABLE 7 Transmittance Data of Glass and Plastic Materials

TABLE 8 Typical Light Loss Factors for Daylighting Design

TABLE 9 Reflectances of Building Materials and Outside Surfaces

TABLE 10 Coefficients of Utilization for Sky and Ground Components for Five Interior Locations

TABLE 11 Illuminance Values for Winter and Spring in Seattle, Washington, at Five Reference Locations

TABLE 12 Illuminance Values for Clear Sky Conditions on June 21 at Five Reference Locations

11. DAYLIGHTING SIMULATION PROGRAMS

Until recently, daylighting simulation tools were too expensive and complex to use for day-to-day designs, and they were primarily used by lighting consultants or researchers. Computer rendering tools have been developed so that many simulation programs now provide realistic visual daylighting output with varying degrees of accuracy. Computational approaches can simulate the distribution of light from both daylight and electric sources, for any selected season, time of day, and building location (orientation and latitude). Many of these programs use radiosity techniques. Radiosity-based renderings are produced by dividing all the surfaces in a scene into a mesh of small polygons. Each polygon takes on a different value of light absorption/reflection, depending upon its relationship to a light source and its surface parameters. These values simulate the light distribution throughout the scene. The following are some commonly used programs; selected characteristics and features are compared in TABLE 13.

TABLE 13 Comparison of Processing Features for Daylighting Simulation Programs

FIG. 34 (a) Rendering of shading provided by the blinds at the New York Times building. (b) Rendering study of veiling reflections on a computer monitor.

FIG. 35 (a) Schematic output showing exploratory rays passing through a window and hitting an external obstruction. (b) Daylight factor distribution analysis applies a ray-tracing technique using the Building Research Establishment (BRE) Daylight Factor method.

FIG. 36 (a) Radiosity rendering of polygons for a gallery space. (b) Rendering of the same gallery space.

FIG. 37 (a, b) Rendering of daylight in a residence.

FIG. 38 (a) Lumen Micro rendering of daylighting in a church. (b) Lumen Designer rendering of electric lighting in an office.

• Desktop Radiance: This program is a Windows version of Radiance that integrates a realistic rendering package (Fig. 34) with a computer-aided design (CAD) input environment. Libraries of materials, glazings, luminaires, and furnishings facilitate data entry.

Lawrence Berkeley National Laboratory, Pacific Gas and Electric, and the California Institute for Energy and Environment developed this program.

• Autodesk Ecotect: is a building analysis software program offering a range of modeling and analysis features such as visualization, shading, shadows, solar analysis, lighting, thermal performance, ventilation, and acoustics. It can export to Radiance for higher-level ray-tracing techniques. Daylighting capabilities can model shadows and reflections on the surfaces of other buildings at a single point in time, show an entire year's shadow patterns for a single surface, model surface solar radiation relative to the effects on thermal mass, and calculate daylight factor (FIG. 35).

• form•Z RenderZone PLUS (form•Z RenderZone PLUS is a modeling and drafting program with photorealistic rendering. It offers the following 3 rendering levels: simple, z-buffer, and ray-trace. Designs can begin with a 3-D model and gradually add features to render with more complexity. form•Z RenderZone PLUS includes "global illumination" techniques, and produces accurate distribution of light in the environment. form•Z RadioZity is the version of form •Z RenderZone that includes radiosity-based rendering. With form•Z RadioZity, lighting conditions can be accurately simulated and incorporated into the rendering. Although familiar to many as an architectural rendering program, it has the ability to accurately show shadows and radiosity rendering (FIG. 36).

• Autodesk 3ds Max Design : Autodesk 3ds Max Design includes 3-D modeling, rendering, and animation. Autodesk VIZ (FIG. 37) has migrated to Autodesk 3ds Max Design, which continues to offer a specialized visualization and rendering program that includes lighting effects from indirect illumination and shadows under varying conditions of daylight and electric light, as well as expanded imagery and cinematographic effects.

• Lumen Micro 2000 and Lumen Designer: Lumen Micro 2000 (FIG. 38) operates in a Windows environment and can provide detailed daylighting analysis. There is an extensive product library with luminaire data from over 70 manufacturers.

Lumen Designer is the most recent generation of software (although Lumen Micro 2000 is still available). It can create any geometry, produce realistic renderings, interface with product data bases from industry, and calculate daylighting.

After 2008, Lumen Micro and Lumen Designer licensing will be supported by LTI Optics, and users will be encouraged to migrate to LAI's AGi32 lighting software.

• AGI32: Lighting Analysts, Inc. offers this software program for lighting calculations and renderings of electric lighting and daylighting systems. It is widely used in the lighting industry and includes a Web-based interface that allows users to access manufacturers' photometric data and provides for easier updating.

12. PHYSICAL MODELING

Physical models are a useful and indispensable tool for the investigation of complex daylighting phenomena. Simple physical models can give both the designer and the client a visual understanding of a day-lighted space. Physical models can duplicate the lighting phenomena that would occur in a full-scale space and, when placed under identical sky conditions, will yield accurate results relative to brightness, shadows, and daylight factor. By changing window design or orientation, adding lightshelves, reflectors, or shading devices, and/ or modifying surface materials, a designer can quickly produce a three-dimensional visual image that displays qualitative and quantitative performance results for a proposed daylighting design.

The advantages of physical models include:

• The opportunity for accurate daylight measurements and for qualitative evaluation

• Easy construction (for most designers)

• Crude models that can yield critical information

• Easy comparisons of various schemes (e.g., interchangeable wall or ceiling elements)

• Realistic visualization for clients

The principal disadvantage of using physical models is the need to expose them to the desired sky conditions. For example, waiting for suitable sky conditions in order to view a particular space under both overcast and clear sky conditions, or at different seasons of the year, or during different times of day, is not always practical.

Constructing scale models is relatively simple, using corrugated cardboard, mat board, and colored paper-mounted on a base for ease of manipulation (FIG. 39). The model should be made modularly so that alternative design proposals can be inter changed. For example, to compare various skylight configurations, several replaceable roof configurations can be constructed. Model size depends upon the size of photometers used to measure interior illuminance, the size of the space, and the need to accommodate a camera viewport. Considering ease of construction and visualization opportunities, bigger is usually better-although larger models are often preceded by smaller/cruder study models.

Cardboard is an ideal material for daylighting models because it is opaque, unlike foam core board, which is translucent and transmits some light. Unintentional light leaks must be prevented, typically by sealing the joints of a model with black electrician's (or duct) tape or by using strips of black cardboard to close gaps. "Portholes" in one or both of the long sides of a model (approximately 2 in. [50 mm] in diameter) will accommodate visual inspection and insertion of a camera lens to photo graph the distribution of light. Model surface reflectances (both interior surfaces and exterior surfaces that contribute to daylight distribution) should be the same as those proposed for the actual building (see Table C.27 for reflectances and mat board colors). Special care should be taken to accurately replicate details around daylight openings-the size and depth of mullions, the depth and reflectivity of the sill, louvers, shading devices, and surfaces just outside daylight openings. Any major furnishings that might have a significant impact upon light distribution should also be included.

FIG. 39 These photographs illustrate the effectiveness of even a crude model in daylighting studies. (a) A real faculty office at the University of California-Berkeley served as an exercise for a daylighting study. (b) The scale model for this office was constructed of cardboard. Significant reflecting surfaces such as desk surfaces and windowsills were carefully modeled. (c) A quick modification to the model introduced light washing along the wall from a skylight above (upper left of photo) so that the rear of the office would receive more light. All photos were taken on site at midday on an overcast day.

FIG. 40 ShadowTracker heliodon at the Baker Lighting Lab at the University of Oregon. Automated adjustments for latitude, elevation, and tilt permit exposure of the model to desired clear sky conditions.

Daylight model testing may be conducted under a real or an artificial sky and may also involve heliodon studies.

1. Use of a real sky with daylighting models is logical but often difficult to coordinate (as described above).

2. Artificial sky or mirror box. Carefully designed and controlled artificial sky domes or a mirror box can duplicate overcast sky conditions with a high degree of accuracy and are ideal for testing physical models. A number of such units exist in major universities and lighting laboratories around the world. Sky domes are usually illuminated by interior perimeter lamps with the model located in the center.

A mirror box is essentially a room with a luminous ceiling (using fluorescent lamps) and mirrored walls to create a sky with an "infinite" horizon. For construction details, see Moore (1985).

3. Heliodon. The heliodon, as shown in FIG. 40, is a sophisticated device that allows the study of shading and solar access for a specific latitude, time of day, and time of year using architectural scale models. It operates by rotating and tilting a building model with respect to the real sky or an "artificial sun" (a narrow beam electric light source) until the desired solar altitude and azimuth are reached. Over the years, heliodons (sun machines, sun tables, helioluxes, sun emulators) have been built using a variety of configurations to simulate the sun's position relative to an architectural scale model. In all cases, the device establishes a geometric relationship for three variables: site location (latitude), solar declination (time of year), and the Earth's rotation (time of day). By adjusting any one of these variables, a heliodon can simulate sunlight penetration and shading for any combination of site location and time. Other types of heliodons keep the position of the model fixed and use a band of lamps that move along three axes to simulate the sun's position for different times and seasons.

FIG. 41 (a) Shaded walkway at the Horseshoe Lodge, Beulah, Colorado. (b) Sidelighting in dormitory room of this summer camp.

13. RECAPPING DAYLIGHTING

This Section began by describing the control of daylight in buildings as both an art and a science. Daylighting is a cornerstone of green design and a major contributor to good building energy performance, as well as occupant com fort, productivity, and health. Addressing day lighting early in schematic design is a critical step for successfully zoning activities and massing the building to optimize the use of daylight and minimize the use of electric lighting. Skill fully employing strategies such as top-lighting, sidelighting, lightshelves, and shading devices involves numerous qualitative judgments and quantitative calculations to achieve design intents and criteria. While it is important to con duct necessary calculations, it is also important to recognize the beauty in the simplicity of the straightforward design of the past-as shown at the historic Horseshoe Lodge, built in 1939 (FIG. 41).

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FIG. 42 (a) Audubon House, headquarters for the National Audubon Society, located in New York City, is a reused and renovated building. (b) Lobby space uses daylight from high windows and skylight.

FIG. 43 (a) Office space along the south-facing façade of Audubon House. (b) Daylighting section showing illuminance measurements.

FIG. 44 (a) Illuminance contours in Audubon House during an overcast day. (b) Illuminance contours during a clear day.

FIG. 45 Recycling bins in the Audubon House basement receive materials sorted by categories of waste (paper, glass, and newspaper).

======

14. CASE STUDY-DAYLIGHTING DESIGN

Audubon House

PROJECT BASICS

• Location: New York City, New York, USA

• Latitude: 40.5º N; longitude: 74º W; elevation 87 ft (26.5 m)

• Heating degree days: 4805 base 65ºF (2672 base 18.3ºC); cooling degree days: 3634 base 50ºF (2019 base 10ºC); annual precipitation: 47 in. (1200 mm)

• Building type: Adaptive reuse

• 98,000 ft 2 (9104 m^2); eight occupied stories

• Completed December 1992

• Client: National Audubon Society

• Design team: Croxton Collaborative, Architects (and consultants)

Background and Context. Audubon House is a restored and remodeled century-old Romanesque building in New York City. The National Audubon Society wanted a headquarters to reflect their environmental mission to restore ecosystems and ensure a healthy environment for people, wildlife, and natural resources. The design team and the client worked together to create a place that served as a model for energy efficiency and environmental responsibility, and to enforce the model. The Croxton Collaborative brought in many design lessons about energy efficiency and environmental performance learned from the redesign and renovation of the Natural Resources Defense Council (NRDC, another New York-based environmental group) building in 1988, just prior to the beginning of the Audubon project. Placing environmental criteria as a priority for the design in terms of resources, energy efficiency, air quality, and occupant well-being set the stage for the development of many new green office buildings. A case study of Audubon House won first place in the 1998 Vital Signs Case Study Competition. The following information is extracted from Audubon House (National Audubon Society, 1994) and information sheets.

Design Intent. The design of Audubon House took the approach of developing a "living model" in four environmental dimensions: energy conservation and efficiency, creating a healthy indoor environment, resource conservation and recycling, and reducing negative environmental impacts-an antidote to the plague of standard-issue, grossly inefficient office buildings that dot urban and suburban landscapes. The motto was "Green design is affordable." Compared to code-com pliant buildings in New York City at that time, Audubon House was designed to use 62% less energy overall and deliver 30% more outdoor air to its occupants.

Design Criteria and Validation. Benchmarks were set for building systems, materials, and strategies based upon previous experience. The criteria included a target of 0.97 W of electric lighting per square foot (conventional buildings at that time used as much as 2.4 W/ft^2); an in-house recycling system that would capture 80% of the office refuse (mostly paper); 26 cfm (12.3 L/s) of outdoor air per person, which would exceed the existing standards and guidelines (then 10-20 cfm); pendant ceiling fixtures reflecting 88% of the light from the fix ture up to the ceiling; and occupancy sensors that would turn off lights in unoccupied zones.

Post-Occupancy Validation Methods. Even with recent developments in environmental technology, Audubon House continues to serve as a model.

Several New York City projects have applied the principles used in this project. Five years after the renovation was completed, an occupant survey found a high degree of satisfaction with daylight quality and availability in the work spaces. The farther a workstation was located from a window, the more often occupants used their task lights.

Several nonfunctioning occupancy and daylight sensors reduced the potential of the daylight integrated lighting system; the lighting power density, however, was calculated to be 0.82 W/ft^2, which exceeded the design goal of 0.97 W/ft^2 and the ASHRAE Standard 90.1 recommendations. In 1996 a separate detailed study on indoor air quality was conducted as part of a larger study of air quality in green buildings.

KEY DESIGN STRATEGIES

• A gas-fired absorption chiller-heater uses no CFCs, emits no sulfur dioxide, and emits 60% less nitrogen oxides than conventional units. Additionally, no CFCs are used in the insulation.

• To promote a healthy environment, natural and recycled materials were used for the furnishings and renovation materials, such as Air-Krete wall insulation, wool rugs without adhesive backing, wood and fabric furniture, and recycled-content countertops and tiles.

• A daylight integrated lighting system producing lowered electricity use during daylight hours through the use of light-colored furnishings and interior surfaces, a layout of interior work areas to ensure that daylight is not blocked by walls and corridors, pendant up-light ceiling fixtures with fluorescent lamps, daylight dimming sensors, and occupancy sensors in all work spaces (producing what is affectionately known as the "Audubon flap").

• There were low VOC emissions from building materials and furnishings, high-efficiency filters to remove particles, and air intakes on the roof rather than at street level.

• Recycling the entire building by adaptive reuse reduced embodied energy costs, as did the use of recycled materials (Homasote sub floor from 50% recycled newsprint, tiles from lightbulbs, bathroom countertops from plastic containers, etc.) and the provision of an in house recycling system.

FOR FURTHER INFORMATION

National Audubon Society. 1994. The Audubon House: Building the Environmentally Responsible, Energy-Efficient Office. John Wiley & Sons. New York.

Vital Signs Case Study:

Update: The National Audubon society purchased and renovated the case study building at 700 Broadway in New York City in the late 1980s. It was considered one of the first green buildings in New York City. They have recently relocated to a new, 27,500 square foot (2555 m^2) office headquarters at 225 Varick Street in New York City. The new headquarters achieved a LEED® Platinum Certification for Commercial Interiors in 2009.

References / Resources

Brown, G. Z. and M. DeKay. 2000. Sun, Wind & Light: Architectural Design Strategies, 2nd ed. John Wiley & Sons. New York.

Bryan, H. and S. M. Autif. 2002. "Lighting/Daylighting Analysis: A Comparison," in Proceedings of the National Solar Energy Conference. American Solar Energy Society. Boulder, CO.

CIE. 1970. Daylight, International Recommendations for the Calculation of Natural Daylight (Publication No. 16 E-3.2). Commission Internationale de l'Eclairage. Paris.

DeKay, M. 1992. "Volumetric Implications and a Rule-of-Thumb for Thickness of Atria Buildings," in Proceedings of the 17th National Passive Solar Conference. American Solar Energy Society. Boulder, CO.

Dresler, A. 1963. Daylight Design Diagram. Service Division, Commonwealth of Labor and National Service. Melbourne, Australia.

Heschong Mahone Group. 1999-2003. Executive summaries and reports available from:

PIER.htm Hopkinson, R. G., R. Pethebridge, and J. Longmore. 1966. Daylighting. Heinemann. London.

IESNA. 1994. Recommended Practice for the Calculation of Daylight Availability (RP-21-84; reaffirmed 1994). Illuminating Engineering Society of North America. New York.

IESNA. 1999. Daylighting (RP-5-99). Illuminating Engineering Society of North America. New York.

IESNA. 1989. Recommended Practice for the Lumen Method of Daylight Calculations (RP-23-89). Illuminating Engineering Society of North America. New York.

International Energy Agency. 2000. Daylight in Buildings: A Source Book on Daylighting Systems and Components. International Energy Agency, Solar Heating and Cooling Program, Energy Conservation in Buildings and Community Systems.

Lam, W. 1986. Sun-lighting as Form giver for Architecture. Van Nostrand Reinhold. New York.

Millet, M. S., and J. R. Bedrick. 1980. Graphic Daylighting Design Method. Lawrence Berkeley Laboratory/ U.S. Department of Energy. Washington, DC.

Moore, F. 1985. Concepts and Practice of Architectural Daylighting. Van Nostrand Reinhold. New York.

National Audubon Society and the Croxton Collaborative. 1994. Audubon House: Building the Environmentally Responsible, Energy-Efficient Office. John Wiley & Sons. New York.

Stein, B. and J. Reynolds. 1992. Mechanical and Elec trical Equipment for Buildings, 8th ed. John Wiley & Sons. New York.

Windows and Daylighting (Lawrence Berkeley National Laboratory): Whole Building Design Guide (daylighting)

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