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Daylight harnessing

Daylight harnessing technologies are applied to bring diffused daylight into the building interior. There are many available methods and technologies available to harness daylight and this section covers three selective technologies, which are commonly found in good practice and yet highly applicable in developing countries. They are light shelves, light pipes and skylights. They can be deployed independently or in combination, depending on the building’s configuration and functions.

Introduction top

Light shelves. Light shelves in their simplest form, are specially-designed sun-shading devices, placed on the upper part of windows/glazing façades above eye level. While the natural lighting conditions under light shelves near the window is saturated and glare is circumvented, diffused daylight is reflected on the top of the light shelves to the ceiling area (near the window) and further reflected into the interior spaces. To be efficient, the top surface of light shelves is often painted with a bright colour, or have reflective materials attached, e.g., reflective stainless steel, or even mirrors.

Skylights. Skylights are often located on the upper horizontal plane of buildings, filtering and bringing natural lighting into the building from the roof or any horizontal plane of buildings with good exposure to daylight.

Light pipes. This feature consists of an external transparent dome, a reflecting metal pipe and a diffuser to be installed on ceiling. The dome collects and magnifies external daylight, which is transmitted through the internal reflective metal pipe to the diffuser, which in turn distributes the diffused daylight to the internal space below.

illustration © climatetechwiki.org

Figure 1: Light shelf, skylight and light pipe

Feasibility of technology and operational necessities top

Daylight harnessing technologies are suitable for application in all climatic regions. Their contributions can be more impactful in temperate regions where daylight hours are short during cold winter. In terms of functional spaces, these technologies are more suitable for areas where some degrees of fluctuation in illumination intensity are less noticeable and acceptable to the occupants, such as public spaces, atria, retailing areas, carparks, etc. (BCA, 2007).For functional spaces that require more constant lighting conditions, such as laboratories and office spaces, daylight harnessing technologies can be deployed in tandem with artificial lighting to reduce lighting energy demand.

In order to enhance the day lighting performance of an internal space, daylight harnessing technologies can be used in conjunction with high reflectance values for room surfaces. As a rule of thumb, reflectance of walls is above 50%, and that of ceilings is 80% or higher (Ander, 2008). As lighting reflective materials and glazing are sensitive to dirt (which can reduce their performance dramatically) regular maintenance and cleaning are required.

illustration © climatetechwiki.org

Figure 2: Reflective interior finishes enhancing day lighting performance in Zuoying Station, Kaohsiung City, Taiwan

Light shelves can take various forms and be installed in various positions in the façade. For example, they can be: integrated with sun shading devices outside and in front of the façade; diffusive reflective blinds in between space of double glazing façade systems; or be inside the room. If installed externally, light shelves’ materials and configurations should be designed to avoid creating glare for neighbouring buildings. It is also important not to maximise the use of light shelves at the expense of other environmental performance. For example, in order not to compromise thermal comfort due to heat gain on hot afternoons, windows and thus light shelves should not be installed on the west-facing façade.

Skylights are most appropriate for temperate regions, where winter daylight hours are short and heat gain in summer is less severe compared to hot climatic regions. The technologies are often considered inappropriate in hot climatic regions, due to the fact that skylights bring both sunlight and heat into a building’s interior spaces. However, if strategically designed, placed in the shaded roof areas, and a double-glazing system is used, skylights can provide intended benefits to energy efficient buildings.

illustration © climatetechwiki.org

Figure 3: Skylights allowing daylight into the interior of Changi Airport Terminal 3, Singapore.

Light pipes are suitable for all climatic conditions due to new technology that overcomes many shortcomings of skylights. Firstly, due to its narrow and compact size, light pipes can economically address the heat gain and potential water leakage issues found in skylights. Secondly, light pipes are also less prone to break. Furthermore, light pipes do not provide a visual connection between the interior and external environment, and thus are preferred for application in high security and private areas.

Because daylight harnessing technologies have been in the market for a long time, the technical aspect of their implementation can be supported by most markets and regions. Their widespread implementation requires institutional support, including appropriate regulations by local authorities regarding planning, building and construction. These regulations should include but are not limited to:

  1. Adequate spacing between buildings in according to building height
  2. Safety aspects related to the installation of daylight harnessing technologies
  3. Preventing over-glaring and direct reflection to the immediate neighbours of the buildings with light shelves.

It is also very helpful if local building codes (standards) are accompanied by guidelines on day lighting design and methodology for day lighting computation, such as the Indian Standards-SP-41 (Bureau of Indian Standards, 1987).

In regions where daylight harnessing technologies are not commonly used, both research and development as well as capacity building for the local building and construction professionals are required prior to large scale deployment of the technologies. Research and development sets the platform for local data collection and local technology development, especially in the areas of local solar illumination and estimating daylight availability. This data will inform practitioners of the most suitable daylight harnessing technologies and system designs for large scale implementation.

Capacity building is also required in the area of design and analysis tools for designers (e.g., hand drawing methods, computer simulation of day lighting design, as well as its impacts on building thermal performance), installation techniques for local construction workers, and maintenance procedures for building owners and facility management personnel.

Status of the technology and its future market potential top

These three daylight harnessing technologies are proven technologies. The advanced development moves from static features to operable, intelligently-controlled and longer light transmitting distances.

Light shelves. Static light shelves are usually fixed sun shading devices. They are proven technologies and have been widely applied. Movable light shelves are mechanically controlled or sensor-controlled to track the sun angles at different time of day and different seasons of the year. This is designed to allow diffused daylight to enter the building’s interior, while safeguarding the areas near windows from undesirable direct and hot summer sunlight and glare issues.

Skylights. Skylights consist of glazing (often insulated) supported by aluminium frames. Skylights can be considered as roofs and are therefore exposed to outdoor weather conditions, such as intensive sunlight and a large volume of rainwater. However, thanks to its long history of use, the technology has overcome the problem of water leakage and hail damage, rain-noise and other thermal-related issues. State of the art development includes the use of electrified glazing and external and an internal lighting sensor to control the quantity and quality of natural lighting entering the building’s interior. Advanced skylights incorporate heliostat panels, which track sunlight to enhance lighting performance. Early and late in the day when the sun is low in the horizon, the heliostat aligns with the position of the sun to capture and reflect light through the skylight. Under excessive sunlight conditions, heliostat panels can be positioned to block the sun’s rays, and reflect diffused light using reflective material at the back of each reflector panel.

Light pipes. The key objective and advantage of light pipes is to collect sunlight/daylight with a small roofoccupied area, and transmit the magnified light into the building interior. State-of-the-art light pipes use fibre optics to reduce light loss in transmission and to transmit these over long distances (e.g., multiple floors).

Light shelves and skylights have been widely used in developed and industrialised countries. They are often referred to as good design practice, and are well-liked by both design professionals and building users, due to the psychosomatic benefits associated with natural light in the building. On the other hand, light pipes have a low market penetration status. This is because they are a relatively new technology, have a mechanical appearance, and are often seen as an add-on feature by building developers. They are often removed in value engineering, or cost-cutting exercises during the later stage of design development, and do not end up being implemented.

All three daylight harnessing technologies have high market potential in developing countries. The technologies have a high level of acceptance, because the principle of bringing natural light into building interiors can be found in most traditional building methods around the world.

From the climatic influence viewpoint, the high potential market for skylights is in temperate climate regions, due to the fact that skylights can bring large amounts of natural daylight to large interior spaces during a long winter with short sunlight hours. Likewise, light shelves have high potential in tropical and sub-tropical regions, where they can deliver daylight deep into a building’s internal spaces while preventing glare for internal areas near windows. Light pipes, from a functional viewpoint, have a potential market in urbanised areas, where light pipes can take up small amount of roof space and transmit light through several floors.

How the technology could contribute to socio-economic development and environmental protection top

Daylight harnessing technologies help reduce energy consumption by reducing artificial lighting requirements and thus the heat generation from artificial lighting. The US Green Building Council estimates that a 50 to 80% reduction in lighting energy load can be achieved from a well-designed daylight-lit building (USGBC, 1996). In the tropical city of Bangkok, daylight potential is high and is suggested that it can suffice for 95% of the occupancy period of a typical office building if it is well designed (Tanachaikhan et al., 2009). Such energy saving will help to reduce the operational cost for the building owner, as well as GHG emissions.

In addition to the above mitigation potential, daylight harnessing technologies offer building occupants a connection to dynamic temporal outdoor illumination. Such improved natural light provision offers positive psychological effects to building occupants, and “has a great influence on the user’s ability to perform at work and feeling of wellbeing, leading to an increase in productivity” (Hausladen et al., 2005).

With the above contributions, daylight harnessing technologies are not only a mitigation source with good economic sense, but also contribute positively to building occupants’ well-being.

Financial requirements and costs top

Products and installation costs vary in accordance to the daylight harnessing technologies, design configurations, types of materials (e.g., anodised aluminium frame, powder coated aluminium frame, timber frame, glass, etc,) and quantity of materials used.

External static light shelves can be considered the most cost competitive technology, due to the simplicity of the technology and that they can also act as sun shading devices. In their simplest form, light shelves only require the selection of appropriate reflective materials to bounce daylight into the building interior. Skylights are more costly due to their complicated construction methods and stringent material selection to address safety and water leakage issues. Light pipes are pre-designed and ready-to-use products, therefore the product prices are more predictable. In Eastern Europe, for example, the prices of a light pipes can range from about US$150/each at the lower end to over US$600/each, plus installation costs.

For all three daylight harnessing technologies, regular cleaning is required. This is particularly so in more dusty environments, where maintenance should be carried out at shorter intervals, so that the technologies can meet their expected performance.

References top

Ander D. G. (2008). Daylighting. In Whole Building Design Guide. USA: Whole Building Design Guide. [Online]: www.wbdg.org/resources/daylighting.php

BCA (2007). Green Building Design Guide – Air-conditioned Buildings. Singapore: Building and Construction Authority

Bureau of Indian Standards (1987). SP: 41 (S&T) -1987 - Handbook on functional requirements of buildings. New Delhi.

Hausladen G., Saldanha M., Liedl P. & Sager C. (2005). Climate Design: Solutions for Buildings That Can Do More with Less Technology. Munich: Birkhauser.

Tanachaikhan L., Kumar S. (2009). Day lighting for Energy conservation in the tropics: a study on the influences of window configurations and shading devices. International Journal of Engineering Systems Modelling and Simulation, Vol. 1,p.144-159.

USGBC (1996). Sustainable Building Technical Manual (SBTM). USA: Public Technologies Inc., US Green Building Council.