Windows
Main article: Window
Windows are the most common way to admit daylight into a space. Their vertical orientation means that they selectively admit sunlight and diffuse daylight at different times of the day and year. Therefore windows on multiple orientations must usually be combined to produce the right mix of light for the building, depending on the climate and latitude. There are three ways to improve the amount of light available from a window:
Place window close to a light colored wall.
Slant the sides of window openings so the inner opening is larger than the outer opening.
Use a large light colored window sill to project light into the room.
Adjustable light reflector
Different types and grades of glass and different window treatments can also affect the amount of light transmission through the windows.
Light reflectors
Once used extensively in office buildings, the adjustable light reflector is seldom in use today having been supplanted by a combination of other methods in concert with artificial illumination. The reflector had found favor where the choices of artificial light provided poor illumination compared to modern electric lighting.
Light shelves
Main article: Architectural light shelf
Light shelves are an effective way to enhance the lighting from windows on the equator-facing side of a structure, this effect being obtained by placing a white or reflective metal light shelf outside the window. Usually the window will be protected from direct summer season sun by a projecting eave. The light shelf projects beyond the shadow created by the eave and reflects sunlight upward to illuminate the ceiling. This reflected light can contain little heat content and the reflective illumination from the ceiling will typically reduce deep shadows, reducing the need for general illumination.
In the cold winter, a natural light shelf is created when there is snow on the ground. As the outside temperature drops below freezing, moisture in the atmosphere precipitates out, often in the form of snow (or freezing rain). This makes the ground highly reflective. Low winter sun (see Sun path) reflects off the snow and increases solar gain through equator-facing glass by one-to-two thirds which brightly lights the ceiling of these rooms. Glare control (drapes) may be required.
Skylights
A skylight and the optimal placement thereof
Skylights are horizontal windows or domes placed at the roof of buildings, often used for daylighting. White translucent acrylic is a 'Lambertian Diffuser' meaning transmitted light is perfectly diffused and distributed evenly over affected areas. This means, among other advantages, that light source quality standards are measured relative to white acrylic transmission. White acrylic domes provide even light distribution throughout the day. Skylights admit more light per unit area than windows, and distribute it more evenly over a space.
Construction of a DIY skylight
The optimum number of skylights (usually quantified as "effective aperture") varies according to climate, latitude, and the characteristics of the skylight, but is usually 4-8% of floor area. The thermal performance of skylights is affected by stratification, i.e. the tendency of warm air to collect in the skylight wells, which in cool climates increases the rate of heat loss.[citation needed] During warm seasons, skylights with transparent glazings will cause internal heat problems, which is best treated by placing white translucent acrylic over or under the transparent skylight glazing.
Skylights can also double for natural ventilation systems
The amount of light inefficient transparent glazing skylights deliver peaks around midday, when the additional light and heat it provides is least needed. Some skylight designs use domed or pyramidal shapes along with prismatic or other light-redirecting glazings to attempt to validate 'daylighting expert' value. Like automated controls, attempts to achieve more value through expensive additional systems rarely, if ever, validate 'daylighting expert' worth.[citation needed]
Poorly constructed or installed skylights may have leaking problems and single-paned skylights may weep with condensation. Using skylights with at least two panes and a heat reflecting coating will increase their energy efficiency.
Light tubes
Main article: Light tube
This section is written like an advertisement. Please help rewrite this section from a neutral point of view. (February 2010)
Light tube illustrated
Another type of device used is the light tube, also called a solar tube, which is placed into a roof and admits light to a focused area of the interior. These somewhat resemble recessed ceiling light fixtures. They do not allow as much heat transfer as skylights because they have less surface area.
The newest and most exciting technology in this category is the Tubular Daylighting Device (TDD). A modern technology, the TDD behaves in a matter far different from that of its unit skylight cousin. While TDDs and unit skylights both provide daylight from a building roof, there are more differences between the products than similarities. The standard Tubular Daylighting Device model is a passive system consisting of a transparent, roof-mounted dome with self-flashing curb, reflective tubing and a ceiling-level diffuser assembly that transmits the daylight into interior spaces. With the latest in product advancements, today designers find that they are no longer bound by traditional daylighting methods and can bring the benefits of daylight to every occupant in the buildings design easily and effectively with TDDs.
Clerestory windows
Main article: Clerestory
Another important element in creating daylighting is the use of clerestory windows. These are high, vertically-placed windows. They can be used to increase direct solar gain when oriented towards the equator. When facing toward the sun, clerestories and other windows may admit unacceptable glare. In the case of a passive solar house, clerestories may provide a direct light path to polar-side (north in the northern hemisphere; south in the southern hemisphere) rooms that otherwise would not be illuminated. Alternatively, clerestories can be used to admit diffuse daylight (from the north in the northern hemisphere) that evenly illuminates a space such as a classroom or office.
Often, clerestory windows also shine onto interior wall surfaces painted white or another light color. These walls are placed so as to reflect indirect light to interior areas where it is needed. This method has the advantage of reducing the directionality of light to make it softer and more diffuse, reducing shadows.
Sawtooth Roof
Another roof-angled glass alternative is a "sawtooth roof" (found on older factories). Sawtooth roofs have vertical roof glass facing away from the equator side of the building to capture diffused light (not harsh direct equator-side solar gain). The angled portion of the glass-support structure is opaque and well insulated with a cool roof and radiant barrier. The sawtooth roof's lighting concept partially reduces the summer "solar furnace" skylight problem, but still allows warm interior air to rise and touch the exterior roof glass in the cold winter, with significant undesirable heat transfer.
Solarium
Main articles: Sunroom and Greenhouse
In a well-designed isolated solar gain building with a solarium, sunroom, greenhouse, etc., there is usually significant glass on the equator side. A large area of glass can also be added between the sun room and your interior living quarters. Low-cost high-volume-produced patio door safety glass is an inexpensive way to accomplish this goal.
The doors used to enter a room, should be opposite the sun room interior glass, so that a user can see outside immediately when entering most rooms. Halls should be minimized with open spaces used instead. If a hall is necessary for privacy or room isolation, inexpensive patio door safety glass can be placed on both sides of the hall. Drapes over the interior glass can be used to control lighting. Drapes can optionally be automated with sensor-based electric motor controls that are aware of room occupancy, daylight, interior temperature, and time of day. Passive solar buildings with no central air conditioning system need control mechanisms for hourly, daily, and seasonal, temperature-and-daylight variations. If the temperature is correct, and a room is unoccupied, the drapes can automatically close to reduce heat transfer in either direction.
To help distribute sun room daylight to the sides of rooms that are farthest from the equator, inexpensive ceiling-to-floor mirrors can be used.
Building codes require a second means of egress, in case of fire. Most designers use a door on one side of bedrooms, and an outside window, but west-side windows provide very-poor summer thermal performance. Instead of a west-facing window, designers use an R-13 foam-filled solid energy-efficient exterior door. It may have a glass storm door outside with the inner door allowing light to pass through when opened. East/west glass doors and windows should be fully shaded top-to-bottom or a spectrally-selective coating can be used to reduce solar gain.
Fiber-optic concrete wall
Another way to make a secure structural concrete wall translucent is to embed optical fiber cables in it. (See Concrete casts new light in dull rooms.) Daylight (and shadow images) can then pass directly through a thick solid-concrete wall. The only drawback is an inability to put insulation on either side of such a fiber-optic concrete wall. One possibility is to insulate it with aerogel after concrete wall construction, for natural daylight with the highest-possible structural security and no glass windows.
Hybrid solar lighting
Oak Ridge National Laboratory (ORNL) has developed a new alternative to skylights called Hybrid Solar Lighting. This design uses a roof-mounted light collector, large-diameter optical fiber, and modified efficient fluorescent lighting fixtures that have transparent rods connected to the optical fiber cables. Essentially no electricity is needed for daytime natural interior lighting.
Field tests conducted in 2006 and 2007 of the new HSL technology were promising, but the low-volume equipment production is still expensive. HSL should become more cost effective in the near future. A version that can withstand windstorms could begin to replace conventional commercial fluorescent lighting systems with improved implementations in 2008 and beyond. The U.S. 2007 Energy Bill provides funding for HSL R&D, and multiple large commercial buildings are ready to fund further HSL application development and deployment.
At night, ORNL HSL uses variable-intensity fluorescent lighting electronic control ballasts. As the sunlight gradually decreases at sunset, the fluorescent fixture is gradually turned up to give a near-constant level of interior lighting from daylight until after it becomes dark outside.
HSL may soon become an option for commercial interior lighting. It can transmit about half of the direct sunlight it receives.
See also
Active daylighting
Passive daylighting
Passive solar building design
Daylight harvesting
Daylight
Sun path
Transom (architectural)
Roof lantern
References
^ Sun/Earth Buffering and Superinsulation page 68 ISBN 0960442243
^ Muhs, Jeff. "Design and Analysis of Hybrid Solar Lighting and Full-Spectrum Solar Energy Systems". Oak Ridge National Laboratory. http://www.ornl.gov/sci/solar/pdfs/Muhs_ASME_Paper.pdf. Retrieved 2007-12-23.
External links
U.S. Department of energy page on passive daylighting
Daylighting, Chapter 2 of the SynthLight Handbook, Low Energy Architecture Research Unit, London Metropolitan University, April 2004
Sun Light Redirecting Devices - examples of geometrical set-up of light shelves etc.
Solar control faades and Daylighting faades, University of California, Berkeley
MIT, Building Technology Program, Daylighting Lab
Categories: Lighting Solar lighting Solar architecture WindowsHidden categories: Articles needing additional references from December 2007 All articles needing additional references All articles with unsourced statements Articles with unsourced statements from June 2009 Articles with unsourced statements from February 2010 Articles with a promotional tone from February 2010 All articles with a promotional tone I am an expert from China Manufacturers, usually analyzes all kind of industries situation, such as rustic chandelier , antique brass chandelier.
Related Articles -
rustic chandelier, antique brass chandelier,
|
