Summary of Application Research of Active Tube Natural Light Introduction System Based on Light Guide Transmission Technology

(*This article is a project funded by the Beijing Natural Science Foundation (the solar light importer provides key technologies for architectural optics in Beijing underground space lighting, subject number 8083028) )

[Abstract] Based on the physical core type, cavity prism type and cavity mirror type three kinds of light guide transmission methods, the paper summarizes the system performance and application analysis of the active active tube type natural light introduction system.
[Key words] active natural light introduction system; solid core type; cavity prism type; cavity specular reflection type

Application Research Overview on Active Tubular Daylight Guidance System Based on Light Transmission Technology
YUAN ZONGNAN ZHANGXIN ZHAN QINGXUAN

ABSTRACT: Based on three kinds of light transmission technology, they are solid core systems, hollow prismatic light guides and hollow mirrored guides respectively. Dissertation summarizes system's performances and application analyses of active tubular daylight guidance system that is now a fully-fledged technology.
KEYWORDS: Active Daylight Guidance System; Solid Core Systems; Hollow Prismatic Light Guides; Hollow Mirrored Guides

According to the concentrating method, the tubular natural light introduction system is divided into active type and passive type. At present, in domestic and foreign applications and research, active light collection is the main direction. This paper mainly discusses the application of active light collection types.

A typical tubular natural light introduction system consists of a three-part technology, including an external concentrator, a light guide transmission device, and an internal illuminator. The key technical components are optical transmission devices connected inside and outside, so-called light pipes. According to the existing technical research and practice accumulation, the optical transmission method and technology can be divided into four categories, namely, beam/lens systems, hollow mirrored guides, and hollow prisms. Prismatic light guides), solid core systems [1]. In practical applications, active light collection combined with solid core, cavity prism and cavity mirror transmission forms several mature integrated systems, including the Japanese “Himawari” system transmitted by fiber. HSL (Hybrid Solar Lighting) system in the United States, Solux system in Germany; European Arthelio system with cavity prism transmission; Swiss Heliobus system with mirror mirror transmission, Heliostats system in Berlin and Malaysia.

1 Active system for physical core transmission

1.1 "Himawari" system

The system was developed and developed by Professor Kei Mori in the 1970s, and its first generation appeared in 1979. The light collecting part of the whole system adopts GPS positioning, convex lens group focusing to enhance sunlight illumination, fiber introduction, and automatic sunlight tracking system [2]. The concentrator is composed of a set of hexagonal Fresnel lenses arranged in a honeycomb shape (Fig. 1). The photosensitive device is placed in the center of the concentrator and has an internal clock and a set of microprocessors for tracking the sun. When the weather is good, the solar sensor can accurately determine the position of the sun; when the sun is blocked by the clouds, the concentrator will rely on the calculation of the internal clock and the microprocessor to adjust the direction, so that the cloud movement leaves, no longer When blocking sunlight, the concentrator can accurately locate the sun; when sunset, the system automatically turns to the direction of the sunrise and shuts down the system to the next sunrise based on the clock and processor calculations. [2]

Figure 1 The largest concentrator in the Himawari system. [2]

Each Fresnel lens on the system concentrator is introduced into a 1 mm diameter fiber by focusing sunlight. Several fibers are bundled to form the light guiding transmission portion of the entire system. The smallest composition consists of six Fresnel lenses combined with six fibers, on the basis of which 12, 18 and other combinations are formed. In addition, the incident end of the optical fiber is precisely positioned on the visible light focus between the purple and infrared rays, and the ultraviolet light is largely intercepted by the physical distance difference positioning, and only 1/2160 of the ultraviolet light is tested to enter the room. At the same time, all radioactive rays such as X, Y, Φ, β, γ, and α in the sun are also excluded [2], and finally a small amount of ultraviolet rays, infrared rays, and a large amount of visible light are entered.

The system application data record shows that when the concentrator receives 98000 lx of solar light, each fiber of about 15 meters can output a luminous flux of 1920 lm under the collection of the lens. The ratio of the diameter of the illumination to the sunlight introduced by "Sunflower" is 1.1:1 [2].

The Himawari system has a strong applicability to spaces that emphasize spectral and thermal control, such as aquariums, photosynthetic cell culture chambers. The standard models of the system are “6 mirrors”, “12 mirrors” and “36 mirrors”. The order products are “90 mirrors” and “198 mirrors”. For operation and maintenance, the Himawari system is relatively simple to maintain and has low operating costs. For example, 12 eyes of "sunflower" use about 11 degrees a year, and the transparent dome of the collection unit can be washed with water [2].

1.2 HSL system

The system was developed to complete an energy-saving program in the United States (which is expected to save more than $500 million and 3 billion kWh by 2020). The HSL system thus developed includes active solar collectors, fiber optic transmission, solar cells, and conventional power. The development and application of the entire system is carried out in institutions such as 3M, Sandia National Laboratory and Oak Ridge National Laboratory.

Similar to the Himawari system, the HSL system's solar concentrator is a set of two-axis day-position tracking devices whose main mirror is designed to be a dish-shaped secondary optical system that reflects the convergence of sunlight into the dish-like focal length. (SOE). The secondary optics selects a cold mirror that separates the visible and near-infrared light of the incident light. The cold mirror splits the visible light portion to a series of fibers with a larger core radius, and the fiber group is placed at the center of the concentrator (Fig. 2). The infrared light is transmitted through the cold mirror into the photocell assembly. Since the photocell is most sensitive to the infrared light, this method can provide electricity to the photovoltaic system to a greater extent [3].

Figure 2 The concentrator of the HSL system. Source:

The basic light transmission portion is composed of 8 fibers each having a diameter of 18 mm. As shown in Figure 3, the eight fiber ports form a circular assembly with a diameter of 54 mm located in the center of the concentrator. The number and size of the specific application of the fiber depends on the size of the dish-shaped main mirror used.

The internal illuminator adopts a composite type, that is, an artificial light source and a natural light combination, and the artificial light source and the optical fiber light-emitting end are disposed together in the diffuser. Artificial lighting is activated when the sun is below the horizon or on a cloudy day. The good mixing of the artificial light source with the natural light depends mainly on the light color of the artificial light source and the setting of the diffuser. The HSL system has developed two different light scattering techniques to make the fiber terminal's illumination form similar to that of a conventional cylindrical fluorescent tube: (1) a cylindrical astigmatism strip (2.54 cm in diameter) is placed in a conventional luminaire, and the other end is connected to a fiber optic terminal. The disadvantage is that the efficiency of the astigmatism strip is only 50%; (2) using the acrylic prism astigmatism device, which has a 15 cm diameter diffuser formed by a micro-optical prism structure, the efficiency of which can reach 90% theoretically. . [4] In order to ensure the stability of the lighting level, the system is equipped with an accurate controller. Even when the clouds temporarily block the sunlight, the controller can automatically adjust the intensity of the artificial light source according to the natural light conditions. The controller also The adjustment control can be turned on and off manually.

Combining the efficiency of the various components of the overall system for light collection, light transmission, and astigmatism (mainly primary mirrors, secondary optics, fiber optic inlets, fiber optic transmissions, and illuminators), the overall system efficiency of HSL systems for single-story building applications is approximately 50%, the overall system efficiency for two-story building applications is about 30% to 35% (affected by light distribution, fiber length). When the 2 square meter concentrator receives 100,000 lx of natural light, it can transmit 100,000 lm and 60,000 lm of luminous flux for one-story and two-story buildings respectively. Assuming 90 square meters of room plane can distribute light evenly, the system can provide one for each. Layer building and two-story building 1000lx and 650lx [5].

At present, the system has been effectively applied to the Sacramento office building in California, the Wal-Mart supermarket commercial building in Texas, and the energy-saving effect is obvious. For example, the Wal-Mart supermarket in McKinney, Texas, uses the HSL system, which is mainly installed in the space dedicated to electrical appliances, and uses spot light to solve the problem that the space cannot be added to the skylight to improve energy saving and lighting; fluorescent light is used as an auxiliary for the entire space. The light source is automatically controlled according to the conditions of natural light. Since March 2007, the supermarket has carried out energy consumption monitoring and performance analysis under the operation of HSL system. In September 2007, HSL system brought more than 50% energy saving effect [6].

1.3 Solux system

The system is an active natural light introduction system developed by Germany's Bomin Solar Research (BSR) based on Fresnel lens technology. The transmission part uses a liquid core light pipe. The concentrator also uses a two-axis mode. The 1 meter diameter Fresnel lens can concentrate 10,000 times of the sun's rays. By setting a layer of filter, it can filter out excess heat before entering the wick channel [7]. The solar position tracking device consists of a daylight positioning sensor and a microprocessor that calculates the position of the sun. The light is concentrated and filtered into the liquid-core light pipe transmission section, which is 2 cm in diameter and filled with a clean liquid composed of several special substances. The light passes through the transmission portion and enters the astigmatic tube device for diverging the illumination indoors. Due to the transmission of the liquid core light guide, the light at the light emitting end is slightly greenish. The transmission loss of light increases with length, and 10 to 15% of light transmission loss occurs every ten meters [8].

The system was first installed at the German Technical Museum in Berlin (Fig. 4). The liquid core light pipe is 5 to 7 meters long and has a diameter of about 20 cm. It is fixed to the roof and suspended indoors. Natural light enters from one end of the liquid-core light pipe, while the other end is connected to an artificial light source as a backup for insufficient natural light conditions. Occasionally, the problem of liquid leakage from the liquid core light pipe in the application is caused by the low outdoor temperature which causes the paraffin to solidify.

2 Active system with cavity prism transmission

The most typical active system combined with prism transmission is the Arthelio system, which was developed to solve the effective combination of artificial lighting and natural light. In the current European system application case, most Asrio systems use active concentrators. The concentrator is generally a large outdoor unit with a large scale, and the internal is a two-axis or single-axis tracking day system for reflecting natural light into the Fresnel lens group. The concentrator can also be equipped with a separately movable secondary concentrator to meet the optimal concentrating.

In the application case of the Technical University of Berlin and Semperlux Lighting in Berlin, after active light collection, the light is transmitted into the transmission part of the cavity prism technology developed by 3M. The Asturian system of the Technical University of Berlin uses 4 square meters of heliostats and secondary concentrators. The lighting space is a small space on the top floor of the building, and the heliostats are placed close to the room. Semperlux's system uses a larger 6-square-meter heliostat, which does not contain a secondary concentrator, and the light is introduced through the heliostats horizontally into four 1.4 x 1 meter Fresnel lenses with a focal length of 1.2 m [ 9], four concave mirrors are provided to direct light into the cavity prism light guide. The entire light collecting device is placed in a device called a “hybrid box” for easy cleaning and maintenance (Figure 5). Among them, a 1000 watt adjustable sulfur lamp is set as a backup light source. The device connecting the mixing box is two 12-meter-long, 30 cm diameter cavity prismatic transmission assemblies. The integrated hybrid light guiding system can meet the lighting needs of different time periods and different seasons [10].

The Austrian Aslio system also uses active light collecting components. The light collection component uses a combination of a daylight tracking system and passive specular reflection (Figure 6). Two sets of adjustable 300 mm cavity prism transmission sections with Fresnel prisms are used. Natural light is introduced into a windowless underground space of 7.8 meters long, 4.5 meters wide and 2.4 meters high. The astigmatism device is realized by a prism wall, and the user can adjust the mirror surface of the indoor device to reflect the introduced sunlight to meet the needs of the working space. At the same time, a supplemental fluorescent lamp system was designed. The entire tubular natural light introduction system can provide 100~1200lx light, and the overall efficiency of the system is about 30% compared to outdoor sunlight conditions. A tubular natural light introduction system like this is also used in other parts of Europe. Through continuous energy consumption monitoring, the statistical display of the relevant lighting energy of this type of introduction system can save 40~60 compared with the traditional electric lighting system. % energy consumption. The combined cost is 225 euros per square meter, ten times the traditional electric lighting system that provides the same level of illumination [11].

Milan's Aslio import system application case is a single-storey warehouse building (Figure 7). The light collecting assembly uses only a single axis light capturing head, which is mainly built on the components of a Fresnel lens. In order to improve the concentrating performance, special mechanical components are designed and added to the concentrating system, enabling them to automatically move according to the sun's rays and obtain a high level of natural light. The entire system is capable of providing 200~250lx illumination for the work surface. Statistics show that the system can replace about 67% of fluorescent lighting equipment in the entire building with the aid of induction and adjustable devices [10].

3 Active system for cavity mirror transmission

Developed in Switzerland and known as Heliobus, this active heliostat system uses a spoon-shaped heliostat attached to the roof of the building and connected to the lower light pipe. The whole system is tightly integrated, and the light is rotated by the spoon-shaped heliostat (Fig. 8) according to the position of the sun to receive the natural light. The spoon-like form can simultaneously concentrate the divergent light and introduce it into a larger square space. The space enters the cavity mirrored light pipe by reflection. The middle of the light guide tube is provided with a connection port, and the light can be transferred according to the requirement of illumination, and the transfer method is to set the horizontal astigmatism strip member. The entire system is a fixed device except for the keyed heliostat [13].

Although Heliostats are collectively referred to as heliostat systems, the above-mentioned, for example, the Asliot or the sunflower system employs a flat lens or a dish-shaped mirror for collecting light. In Germany and Malaysia, the tubular Heliostats system is similar to the Heliobus system developed in Switzerland, and is in the form of a tube, so it is more suitable to combine a fixed, larger radius cavity light pipe.

In Berlin's Potsdamer Platz, the outer perimeter of the space connecting the underground stations is a high-rise building, and the design of the space is expected to introduce natural light into the external landscape, so the three tubular heliostat systems combined with the cavity mirror light pipe are introduced. This space (Figure 9). The fixed-day device uses a flat circular lens instead of a spoon-shaped heliostat. These light pipes are actually formed by two layers of tubes, the outer layer is glass and the inner layer is metal, the interlayer between the two layers is a special high-reflection transparent film, and the inside of the metal layer is covered with a film with higher reflectivity [13] In this case, although the natural light introduction system adopts the active light collection method, the overall efficiency is low, and the greater significance is the system landscape benefit.

Malaysia's Masjid Wilayah Mosque uses 12 sets of heliostat systems to provide natural light for an area of ​​3,600 square meters, the main function of which is prayer and sermon [14]. The roof of the mosque consists of a main dome and three adjacent smaller domes (Fig. 10). A heliostat with a diameter of 1 m is mounted on the top of the central dome, reflecting the sun's rays into a pyramid-like glass space that reflects and transmits light into the prayer hall.

4 Comparison of light guide transmission and light collection components

In practical applications, the components of the system are coordinated and composed. The performance of each part is affected by the efficiency of each part and the efficiency of the combined parts. The comparison analysis of each related component type is as follows:

references

[1] Carter, DJ Developments in tubular daylight guidance systems, Building Research & Information. 2004 (3): 220~234.
[2]http:// 2009.2
[3] John Morris. Oak Ridge National Laboratory. USA. 2009 (3). http://
[4] Muhs, Jeff. Hybrid solar lighting doubles the efficiency and affordability of solar energy in commercial buildings. CADDET Energy Efficiency. 2002b.
[5] Muhs, Jeff. Design and analysis of hybrid solar lighting and full-spectrum solar energy systems. SOLAR2000 Conference. Madison, Wisconsin, USA. 2002.
[6] L. Curt Maxey, Melissa V. Lapsa. et al. Hybrid Solar Lighting: Final Technical Report and Results of Field Trial Program. OAK RIDGE NATIONAL LABORATORY, US DEPARTMENT OF ENERGY, Oak Ridge, Tennessee, USA. 2008(9 ): A-11~A-14.
[7] Jakobiak, Roman. Architect. IBUS (Institut für Bau-, Umwelt-, und Solarforschung), Berlin. 2001 (11).
[8] Claus Colsman-Freyberger. BSR Solar Technologies GmbH. Lörrach, Germany. 2002(02).
[9] Kaase H. et al. Arthelio, ein Grossforschungsprojekt der Technischen Universität Berlin, German. 2000(3): 326~331
[10]Mingozzi, A., Bottiglioni, S. and Casalone, R. An innovative system for daylight collecting and transport for long distances and mixing with artificial light coming from hollow light guides, in Proceedings of the 9th Lux Europa Congress, Reykjavik, 2001(1): 12~21.
[11] Pohl, W. and Anselm, C. Report of EC-funded Joule-Craft Research Project: Development of an Economic and Energy saving Heliostat Technology for Room Illumination. Publishable Final Report, Bartenbach LichtLabor GmbH, Aldrans: 2001
[12] Franta, G., Anstead, K. Daylighting Offers Great Opportunities. American Institute of Architects, Washington, DC: 1993.
[13] Heliobus AG. We bring daylight into the darkness. http:// 2002(3).
[14] Erik Andre Jutta Schade. Daylighting by Optical Fiber. Lileal University of Technology: 2002.

Author: YuanZongNa (YUANZONGNAN)
Gender: Male Date of Birth: March 3, 1965 Work Unit: (Taiwan) Yuan Zongnan Lighting Design Office Address: Room 113, South Building, Tsinghua University, Haidian District, Beijing (100084)
Contact number (office) 13710186866 (mobile)
email:

The second author: Zhang Xin (ZHANGXIN)
Gender: Male Date of Birth: April 26, 1978 Work Unit: School of Architecture, Tsinghua University Address: Room 113, South Building, Tsinghua University, Haidian District, Beijing (100084)
Highest degree: Doctoral title: Instructor contact number (office) 13911524326 (mobile)
email:

The third author: Zhan Qingxuan (ZHANQINGXUAN)
Gender: Male Date of Birth: April 4, 1936 Work Unit: School of Architecture, Tsinghua University Address: Room 113, South Building, Tsinghua University, Haidian District, Beijing (100084)
Highest education: Undergraduate title: Professor (PhD)