A study of horizontal light pipe system for interior daylighting in a dense urban environment

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A study of horizontal light pipe system for interior daylighting in a dense urban environment


Author: Kwok, Chun-man
Title: A study of horizontal light pipe system for interior daylighting in a dense urban environment
Degree: Ph.D.
Year: 2011
Subject: Daylighting.
Interior lighting.
Light in architecture.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xxiii, 167 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2462498
URI: http://theses.lib.polyu.edu.hk/handle/200/6268
Abstract: Daylight is a natural resource for illumination and it is welcomed by all building occupants for its quality, psychological relief and the potential to save energy. Utilization of daylight also helps to alleviate the worsening situation regarding energy shortage, global warming and pollution problems. Hong Kong is one of the high-density cities in the world. Buildings in urban area are densely packed. Windows on vertical facades are the only way to introduce daylight into multi-storey buildings. However, daylight can only penetrate to a limited depth from the window wall. In dense urban areas with heavy obstruction, the daylight penetration depth is further limited. Horizontal light pipes have a great potential to be used for channeling daylight deeper into a room without decreasing the daylight near windows. Daylight availability on building facades were simulated using Radiance for each of the 15 CIE standard sky conditions. Simulations were undertaken for several typical obstructing conditions commonly found in urban environments. A real building was selected for the study of year round daylight availability on its vertical facades. Simulation study using Radiance with Cumulative Illumination Technique (CIT) was also applied to determine the annual daylight availability on building facades in highly obstructed locations. Under CIT, fraction of time with sun positions are suitably divided into altitude and azimuth ranges so that annual prediction of daylight availability can be done in a single simulation. It is found that daylight availability on obstructed building facade is more sensitive to sky patches at higher altitude. Light transport through pipes with rectangular aperture was simulated. The following parameters were investigated with respect to the transmission efficiency of light pipes: width-to-height ratio of the pipe; length-to-width ratio of the pipe, length-to-height ratio of the pipe, reflectivity of the pipe surface, incidence angle of light rays, and shapes of light pipe sections. Reflectivity of the pipe surface is the most influential parameter affecting the transmission efficiency.
To study the internal daylight illuminance, computer modelling analyses were carried out for selected examples of interior spaces installed with light pipe. The predicted illuminance of the room with light pipes was compared with the results of the same room without light pipes under an unobstructed environment. Different facade orientations and sky conditions were accounted for in the simulations. To quantify the daylighting performance of the light pipe, an indicator called relative illluminance (RI) is introduced. RI is defined as the illuminance with light pipe installed to the case without light pipe while the room configuration, surface reflectances and the external environment including the sky conditions, sun location and the obstruction remain unchanged. Results show that when the pipe is extracting light from South under clear sky condition with the sun at high altitude, the leverage in illuminance is highest. Dynamic simulations of indoor daylight availability are carried out using a selected local building under a dense urban environment as an example. The annual daylight availability was predicted with dynamic simulations based on hourly irradiance or illuminance data. Annual illuminance frequency analysis and energy saving prediction were carried out using the results of dynamic daylight simulation. In general, the daylighting performance is higher for those light pipes with more exposure to the sky. Room with window and light pipe aperture facing south performs better than other orientations. A refined physical scaled down model (1:30) of an office space (2.5m high x 5m wide x 9m long) installed with light pipes was constructed using aluminium frames and card boards. Indoor measurements were carried out in a dark room in which the model room was mounted on the rotary arm of a goniophotometer so that it can be rotated freely and accurately under computer control along the vertical and horizontal axes. By rotating the arm along different axes, various values of solar altitude and azimuth were simulated with a 100W tungsten lamp fixed in location. Data obtained from experiment were compared with simulation results.

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