- Shopping Bag ( 0 items )
Daylighting is the process of incorporating natural lighting into the design of buildings. The new edition of this concise resource makes theory, calculations, and execution crystal clear with straight-to-the-solution examples and uncluttered language. In a practical, applied approach, this book covers daylighting strategies, materials, and methods of construction, including significant advances in lighting and daylighting technology.
In a unique design-manual format that includes ample illustrations and white space for sketches and notes, Ander shows readers how to embrace the light with architectural design. From evaluation to execution, the book is a veritable catalog of daylighting strategies, materials, methods of construction, and significant technological advances.
As a design feature, the use of daylighting within a building creates a more pleasing and productive atmosphere for the people within. Daylight provides a direct link to the outdoor environment and natural light delivers a dynamic evolving distribution of light. The moderation of light levels is often subtle and usually unnoticed, and the result is one of visual richness, creating an environment that is stimulating and more comfortable.
Successful daylighting is more than simply adding large windows or skylights. It involves thoughtful integration of design strategies, which address heat gain, glare, variations in light availability, and direct-beam penetration into a building. Design considerations will often address details such as shading devices, aperture size and spacing, glazing materials, interior finishes, and reflectance. In large measure, the art and science of daylighting is not so much about how to provide enough daylighting as how to do so without its possible undesirable effects.
As an efficiency measure, daylighting is most effective during bright sunny afternoons when it can supplant the need for electric lighting entirely. Because an electric utility must provide enough generating capacity to serve the highest demand predicted for its service territory, daylighting has the potential not only to reduce the building's overall energy consumption but also to lower the peak demand.
Electric lighting directly accounts for approximately 20% to 25% of the total electrical energy used in the United States. In the commercial sector, lighting accounts for 37% (34% interior, 3% exterior) of electrical energy consumption (see Figure 1.1). Lighting also has an indirect impact on the total energy use because the heat generated by electric fixtures alters the loads imposed on the mechanical cooling equipment. As a rule of thumb, each unit of electric lighting contributes to an additional one-half unit of electricity for space conditioning because of the contributions from the heat generated by electric lighting. The energy savings from reduced lighting loads can directly reduce air-conditioning energy usage by an additional 10% to 20%.
There seems to be a strong interest in efficiency issues not only from a technical standpoint but also as they relate to social and behavioral issues. These issues often involve enhanced comfort, satisfaction, and productivity and may even have a relationship to the number of workers' compensation claims filed against an employer. The Center for Building Performance and Diagnostics (CBPD) at Carnegie Mellon has conducted many building surveys and postoccupancy evaluations to better understand the effect of design features on occupants. Appendix G contains a survey form developed to assess the impacts of perceived comfort for a series of postoccupancy evaluations conducted at the College of Environmental Design at California Polytechnic State University at Pomona.
Daylighting may potentially play a key role in supporting "sustainable" development. As clients begin to demand sustainable solutions and the design community embraces these challenges to produce buildings that reduce environmental impacts, daylighting solutions have the opportunity to play a significant role through pollution avoidance. By virtue of improving a building's efficiency, you would expect to see a reduction in annual kilowatt-hours so the amount of pollutants emitted at a utility generating station will reduce the amount of airborne pollutants, including nitrogen oxide (N[O.sub.x]), carbon dioxide (C[O.sub.2]), and sulfur dioxide (S[O.su.2]), all of which contribute to reductions in air quality. The Environmental Protection Agency and most utilities have data on the relationship between kilowatt-hours and pollution avoidance values. Table 1.1 represents the latest conversion values for the United States.
A key concern the design team confronts is visualizing various design solutions and quantifying the impacts of fenestration-related decisions. Some design firms regularly perform this type of service as a "basic service," whereas other firms consider it an additional service and obtain additional compensation to cover any added design and analysis time and sell the client based on anticipated reductions in operating costs. Many utilities offer design assistance or incentives to optimize buildings, and these may include assistance to solve for daylighting-related issues. It is important to remember that the daylighting design process involves the ideas of many disciplines, including architectural, mechanical, electrical, and lighting (see Figure 1.2). These design team members need to be brought into the process early to ensure that the concepts and ideas are carried through the entire design, construction, and operating process (see Figure 1.3). Ample opportunity exists for miscommunication throughout the daylighting system design process. The way a building is designed versus how it is built versus how it is operated is important to integrate. Building commissioning is often a critical function to ensure a building performs as designed. See Appendix B for a commissioning specification and prefunctional test protocols.
Architects and designers who are sensitive to basic daylighting fundamentals can achieve an aesthetically pleasing space without sacrificing cost or creativity. An awareness of certain issues that can occur when daylighting is employed will assist in the success of an effective design.
Veiling reflections obscure the details seen by reducing the contrast. Thus, avoid creating conditions within the building where disabling veiling reflections may occur, particularly in spaces where there are critical tasks.
There are many types of visual tasks with various degrees of criticality (see Figure 1.4). A receptionist may not require the same level of illumination as a graphic designer. Many spaces in a building can be lighted that do not require a high degree of illuminance. The Illuminating Engineering Society of North America publishes illumination guidelines for various types of spaces.
Introduce as much controlled daylight as possible, and as deeply as possible, into the building interior. Generally, the human eye can adjust to high levels of luminance without producing discomfort. In fact, the more light available, the better people can see. Veiling reflections and excessive brightness differences are often problematic and should be addressed.
The aim of an efficient daylighting design is not only to provide illuminance levels sufficient for good visual performance but also to maintain a comfortable and pleasing atmosphere that is appropriate to its purpose. Glare, or excessive brightness contrast within the field of view, is one aspect of lighting that can cause discomfort to the occupants of a space (see Figure 1.5).
Although brightness and brightness contrast are important in providing a stimulating visual environment, excessive contrast between foreground and background may disrupt the eye's ability to distinguish objects from their background and to perceive detail. The human eye can function quite well over a wide range of luminous environments, but it cannot function well if extreme levels of brightness are present in the field of view at the same time.
Some contrast in brightness levels may not be undesirable. Dull uniformity in lighting, although never harmful, can lead to tiredness and lack of attention-neither of which is compatible with a productive environment. However, it is necessary to ensure that glare is kept under control and that extreme levels of brightness are not present in the field of view at the same time.
Glare is not a design issue most of the time; it is critical only when certain viewing conditions occur. In this regard, understanding the conditions that might cause glare is the first step toward finding a design solution to deal with it or to avoid the problem altogether.
Glare is a subjective phenomenon and as such is difficult to quantify. Nonetheless, a generalized form of glare quantification can be derived by studying changes in the contrast ratio. The study quantifies the average response of a large number of people to the same glare situation. This type of analysis is used to determine a glare constant for individual apertures and a glare index for all light sources in the field of view.
However, assessments of the physical factors can be correlated to the magnitude of the described sensation so that glare discomfort can be estimated. Studies of these factors have resulted in the development of glare indices, which can be utilized at the design stage to address glare discomfort and are integral to many computer-based design tools.
Sky conditions vary the nature and quantity of the light entering a building. Three types of sky conditions are utilized to estimate illumination levels within a space.
The overcast sky is the most uniform type of sky condition and generally tends to change more slowly than the other types. It is defined as being a sky in which at least 80% of the sky dome is obscured by clouds. The overcast sky has a general luminance distribution that is about three times brighter at the zenith than at the horizon. The illumination produced by the overcast sky on the earth's surface may vary from several hundred footcandles to several thousand, depending on the density of the clouds (see Figure 1.6).
The clear sky is less bright than the overcast sky and tends to be brighter at the horizon than at the zenith. It tends to be fairly stable in luminance except for the area surrounding the sun, which changes as the sun moves. The clear sky is defined as being a sky in which no more than 30% of the sky dome is obscured by clouds. The total level of illumination produced by a clear sky varies constantly but slowly throughout the day. The illumination levels produced can range from 5,000 to 12,000 footcandles.
The cloudy sky has a cloud cover that may range from quite heavy to very light. The cloudy sky is defined as being a sky in which 30% to 80% of the sky dome is obscured by clouds. It usually includes widely varying luminance from one area of the sky to another and tends to change quite rapidly. The cloudy sky may provide periods when direct sun reaches the building site and some periods when, for all practical purposes, the sky appears overcast.
Appendix C gives weather data for a variety of climate zones, including average clear-cloudy conditions. It is quite valuable to perform a climatic analysis to formulate proper design responses.
External obstructions surrounding a window will affect the amount of daylighting entering a space. Many of these conditions, such as cloud cover and sun position, are purely a function of the climate. External obstructions, on the other hand, such as trees and other buildings, can permanently alter the amount of daylight allowed to enter a window opening (seeFigure1.7). The patterns of obstruction will normally vary for each window. They can have different shapes, different positions relative to the window, and different light-blocking or reflecting characteristics.
Increase Perimeter Daylight Zones
Extending the perimeter form of a building may improve the building's performance by increasing the total daylighting area. The trade-offs between an increased perimeter exposure and a compact building form are shown in Figure 1.8. The thermal impact of electric lights and the increased linear footage of window wall should be given careful attention when these strategies are considered.
Allow Daylight Penetration High in a Space
With the location of an aperture high in a wall, deeper penetration will result. There will be less likelihood of excessive brightness in the field of view by reflecting and scattering light before it gets to task level.
Use the Idea of "Effective Aperture" for Initial Estimates of the Optimum Glazing Area
When the effective aperture, the product of the window-to-wall ratio and the visible transmittance of the glazing, is around 0.18, daylighting saturation will be achieved. Additional glazing area or light will be counterproductive because it will increase the cooling loads more than it will reduce the lighting loads.
Reflect Daylight Within a Space to Increase Room Brightness
Although the source of daylight is the sun, surfaces and objects within a space reflect and scatter daylight. An increase in visibility and comfort can be achieved through increasing room brightness by spreading and evening out brightness patterns. A reduction in intensity occurs from reflecting and partially absorbing light throughout a space. A light shelf, if properly designed, has the potential to increase room brightness and decrease window brightness (see Figure 1.9 and 1.10).
Slope Ceilings to Direct More Light into a Space
Sloping the ceiling away from the fenestration area will help increase the brightness of the ceiling farther into a space (see Figure 1.11).
Avoid Direct-Beam Daylight on Critical Visual Tasks
Poor visibility and discomfort will result if excessive brightness differences occur in the vicinity of critical visual tasks. It is a fallacy to believe that good daylighting design entails merely adding large apertures of glazing to a building design. Fenestration controls should be considered if direct-beam illumination is undesirable (see Figure 1.12).
Use Direct Sun Cautiously in Areas Where Noncritical Tasks Occur
Patterns of light and shadows from the sun tracking across the sky can add an exciting and dynamic feature to a space. A feeling of wellbeing and a sense of time and orientation often impact the occupants of such a space. However, if they are integrated poorly, the occupants may have difficulty in seeing, and, in addition, unwanted heat gain may result (see Figures 1.13 and 1.14).
When harshness of direct light is a potential problem, filtering can be accomplished by vegetation, curtains, or louvers. This will help soften and distribute light more uniformly (see Figures 1.15 and 1.16 and 1.17).
Consider Other Environmental Control Systems
Fenestration systems can potentially allow light, heat, air, and sounds into a space. Ventilation; acoustics; views; electric lighting systems; and heating, ventilating, and air-conditioning (HVAC) systems all need to be considered during the design process (see Figure 1.18).
Several design considerations impacting light affect a building in terms of form and shape.
Excerpted from Daylighting Performance And Design by Gregg D. Ander Copyright © 2003 by John Wiley & Sons, Inc.. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Foreword to the Second Edition.
1. FUNDAMENTALS OF DAYLIGHTING.
2. OCCUPANT PRODUCTIVITY AND PERFORMANCE.
Mechanics of Sight.
Colors and Other Vision Factors.
Adequate Lighting and Health.
Light, Workplace Productivity, and Cost Effectiveness.
Heschong Mahone Study.
3. GLAZING PROPERTIES.
Specifying Windows and Glazing.
Gas Fills and Vacuums.
Directionally Selective Materials.
Human Comfort Considerations.
4. INTEGRATION WITH ELECTRIC LIGHTING.
Integration with the EMS.
Integrating the EMS and Lighting Controls.
5. DAYLIGHTING DESIGN TOOLS.
5.1 Hand Calculation Methods.
Worksheet 1: Trial Design Worksheet.
Worksheet 2: Skylight Area Worksheet.
Worksheet 3: Trial Layout Worksheets.
Worksheet 4: Lighting Savings Worksheet.
Worksheet 5: Coooling Calculation Worksheet.
5.2 Computer Programs.
5.3 Daylighting Design Tool Survey.
5.4 Physical Modeling.
6. CASE STUDIES.
Appendix A. Daylighting Feasibility Worksheets and Data.
Appendix B. Standard Commissioning Procedure for Daylighting Controls.
Appendix C. Weather Data.
Appendix D. Glazing Material Properties.
Appendix E. Alternative to Light Savings Graphs.
Appendix F. Daylight Parametrics.
Appendix G. Postoccupancy Visual Comfort Evaluation Form.
Appendix H. Daylighting Design Web Resources.