Basic Research for Performance Evaluation of Light- Shelves according to Reflectivity of Indoor Spaces to Improve Daylighting Performance

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1 , pp Basic Research for Performance Evaluation of Light- Shelves according to Reflectivity of Indoor Spaces to Improve Daylighting Performance Gangmin Jeon 1.1, Heangwoo Lee 1.2, Yongseong Kim Graduate School of Techno Design Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul, Korea wjskm901121@naver.com 1.1, moonup2001@nate.com 1.2, yongkim@kookmin.ac.kr 1.3 Abstract. Studies on building energy savings are continuously carried out, and lighting energy becomes problematic issue, since it accounts for 38% of building energy consumption. In this regard, studies and programs to reduce indoor lighting energy are actively performed. This study undertook an experiment on light-shelf s performance evaluation according to indoor reflectivity to reduce lighting energy consumption and analyzed the depth meeting standard illuminance. The experiment was conducted by adjusting reflectivity of floor, wall and ceiling in the Korean apartment s standard living room area of 54m 2. This study is basic research on the performance evaluation of light-shelf, according to the reflectivity of indoor spaces to improve daylighting performance. The conclusion of the study is as follows: First, average illuminance and uniformity factor showed improvement, when reflectivity drawn by indoor finishing material increased. Second, the depth meeting standard illuminance, 400lx, improved from 2.25m to 3.0m on the summer solstice. Third, 80% reflectivity of ceiling and wall are judged to be appropriate upon fixed type light-shelf installation during the summer solstice. Keywords: Light-Shelf, Interior Finishing Materials Performance Evaluation 1 Introduction According to the research on building energy consumption in the U.S. by IEA in 2011, building energy consumption took up 38% out of total energy consumption, and lighting energy consumption was high at 22% out of the total building energy consumption. Studies to reduce the lighting energy problem are consistently increasing. Especially, various studies on light-shelf are actively conducted thanks to acknowledgment of their efficiency. Existing studies on light-shelf, however, concentrated on performance improvement by such variables as the width, height and angle of a light-shelf, and studies on indoor finishing materials have not been undertaken, which has not brought about efficient energy saving effects. This study carries out the performance evaluation of light-shelf, according to the reflectivity of indoor finishing materials primarily, and then aims to draw the ISSN: ASTL Copyright 2015 SERSC

2 reflectivity of proper indoor finishing materials so as to improve daylighting performance of light shelves. 2 Concept of Light-Shelf and Standard Illuminance 2.1 Concept of Light-Shelf A light-shelf is a natural lighting system introducing natural light deep into indoor spaces through light-shelf s reflection, while interrupting natural light coming into indoor spaces in order to improve a problem of imbalanced illuminance by external direct sunlight. 2.2 Standard Illuminance As shown in Table 1, KS A 3011 presents the illuminance criteria for Korea s residential spaces, and this study set up 400lx, which is living room space s standard illuminance, as the standard illuminance for performance evaluation. Table 1. KS A 3011 Standard Illuminance Criterion [4] Category Location to measure MI (lx) SI (lx) XI (lx) Living room Reading, phone call, makeup 450mm above the floor (MI: Min. illuminance, SI: Standard illuminance, XI: Max. illuminance) 3 Setting Variables for Performance Evaluation and Result 3.1 Setting Spatial Size and Reflectivity for Performance Evaluation As revealed in Figure 1, indoor area set up as 6mx9mx2.5m based on Korea s medium-sized apartment living room to evaluate performance [1], and window area ratio was made 40%[2]. The reflectivity of ceiling and wall were also set, based on existing studies[3], and the reflectivity of wall was set as 80~20% (classified into the unit of 10%) in the case the reflectivity of ceiling was 80%. In the case of 70% and 50% of ceiling reflectivity, this study establish 70~20% of wall reflectivity (classified into the unit of 10%), and 50~20% of wall reflectivity (classified into the unit of 10%). Floor reflectivity was controlled to be 20%, and each reflectivity was adjusted and set as 70.07%, 59.81%, 49.86%, 39.80% and 19.71%, respectively, based on reflectivity of each material provided by RADIANCE. 134 Copyright 2015 SERSC

3 Fig. 2. Setting Space for Performance Evaluation 3.2 Setting Light-Shelf Variables for Performance Evaluation As revealed in table 2, the dimensions of a light-shelf were 300mm in width, 85% in reflectivity and 0 in angle scope, and the light-shelf was located at 1.8m in height in consideration of resident s performance evaluation result and eye-level [5]. Table 2. Setting Light-Shelf Variables for Performance Evaluation Width Height Reflectivity Angle Solar altitude at meridian passage 300mm 1800mm 85% 0 summer solstice: 76.5 winter solstice:: Setting Location to Measure Illuminance As shown in Figure 3, the location to measure illuminance for performance evaluation of a light-shelf for indoor reflectivity, is equally-spaced with 250mm distance from the window, and the number of locations are 175 (5 columns and 35 rows). The height to measure illuminance was 450mm based on the working surface and floor surface, which are illuminance measurement criteria. : Location to Measure Illuminance Fig. 3. Location to Measure Illuminance Copyright 2015 SERSC 135

4 3.4 Performance Evaluation Result of Light-Shelves The analysis on reflectivity of each indoor finishing material and the analysis method in this study are as follows: First, average illuminance according to reflectivity derived by indoor reflectivity is drawn. Second, uniformity factor is found according to indoor reflectivity. Third, spatial depth meeting 400lx, which is the standard illuminance of living room considered above, is derived. The derivation of depth meeting standard illuminance is the quantitative result of a light-shelf, and is also an important factor linked with lighting use [6]. On the summer solstice, the performance evaluation experiment result of lightshelves according to indoor reflectivity is as follows: First, average illuminance rises when reflectivity of ceiling and wall increase during the summer solstice. Average illuminance s change scope by ceiling reflectivity increase is higher than by wall reflectivity increase, therefore, it is advantageous in satisfying indoor illuminance in the case of ceiling reflectivity increase. Second, uniformity factor tends to increase as indoor finishing material s reflectivity becomes higher, and the highest value is revealed, when reflectivity of ceiling and wall are 80%, respectively. However, when ceiling reflectivity is high at 80%, uniformity factor is reduced upon the use of wall finishing material having low reflectivity, which needs to be considered in installing a light-shelf. Third, the spatial depth matching up to standard illuminance moved from 2.25m to 3.0m, according to the increase of reflectivity by each material of wall and ceiling set in this study, which is advantageous to indoor lighting energy reduction in the case of indoor reflectivity increase. Table 3. Illuminance Value, according to Reflectivity on the v and Depth Meeting Standard Illuminance Summer Solstice: (Floor: 20%) R (%) R (%) M.I X.I A.I U.F D(m) F W F W M.I X.I A.I U.F D(m) (R: Reflectivity, F: Ceiling, W: Wall, M.I: Minimum illuminance, X.I: Maximum illuminance, A.I: Average illuminance, U.F: Uniformity factor, D: Depth meeting standard illuminance) 136 Copyright 2015 SERSC

5 4 Conclusion This study is the basic research on the performance evaluation of light-shelf according to indoor space reflectivity, and the conclusion of this study is as follows: First, the improvement of average illuminance and uniformity factor has been shown upon the increase of reflectivity drawn by indoor finishing material. Second, the depth which is fit to standard illuminance, 400lx, improved from 2.25m to 3.0m on the summer solstice, as well as from 4.5m to 5.75m on the winter solstice. Third, 80% of both ceiling and wall reflectivity upon the installation of fixed type light-shelf during the summer solstice, and 80% of both ceiling reflectivity and 60% of wall reflectivity upon the installation of fixed type light-shelf during the winter solstice are judged to be appropriate. This study researched on the basis of indoor finishing material s change ratio; however, study scope needs to be expanded through comparison of user recognition technology and lighting dimming control-applied light-shelf systems in the further study. References 1. Lee, S. Y., Lee, Y. S.: Characteristics of the Interior Space Composition of Apartment in Metropolitan Area, Journal of the Architectural Institute of Korea, (2005) 2. Ministry of Land, Infrastructure and Trensport, 3. Kim, Y. S., Park, B. C., Jeong, K. Y., Choi, A. S.: A Study on the Coefficients of Utilization of Luminaires for an Efficiency Interior Lighting Design, Journal of Korean Institute of Architectural Sustainable Environment and Building Systems, Vol. 2, No. 3, (2008) 4. Korean Industrial Standards, 5. Choi, U. C., Lee, H. W., Seo, J. H., Kim, Y. S.: Performance Evaluation of Energy Reduction of Light-Shelf Applying Punching Plate, Journal of Korea Institute of Ecological Architecture and Environment Vol. 14, No. 6, (2014) 6. Lee, H. W., Kim, D. S., Kim, Y. S.: Simulation Study on the Performance Evaluation of Light-shelf focused on the Depth of Space and the Dimensions and Angles of Light-shelf, Journal of the Architectural Institute of Korea, Vol. 29, No. 3, ( 2013) Copyright 2015 SERSC 137