Sustainable lighting design in school buildings

Transcription

1 Sustainable lighting design in school buildings Ass. Professor Barbara Matusiak, Norwegian University of Science and Technology Department of Architecture and Fine Art Alfred Getz vei 3, 7034 Trondheim, Norway, Dr. Piotr Pracki, Warsaw University of Technology, Faculty of Electrical Engineering Lighting Division Koszykowa 75, Warsaw, Poland, 1. Introduction Worldwide efforts have been undertaken to protect our natural environment. The idea of sustainable development is one of the results of these attempts. Sustainable development indicates a new order developed by countries of the world at the end of the 0th century. Broad ideas usually have many definitions and the like is with sustainable development. The most well-known classic definition was given by Brundtland Commission in 1987: development that meets the needs of the present without compromising the ability of future generations to meet their own needs. In the most general meaning sustainable development means such world s socio-economic development that integrates the political, economic and social activities and natural environment and processes to guarantee possibility of satisfying the basic needs of present and future societies. In order to ensure sustainable development the socio-economic transformations should include: - maintenance of chances of renewable resources reproduction; - effective usage of not renewable resources and replacing them with renewable substitutes; - gradual elimination of danger and toxic materials and substances; - maintenance of ecological safety for people, recognised as creation of friendly conditions for physical, psychological and social health. Buildings and built environment play a major role in the human impact on the natural environment and on the quality of life. Therefore the sustainable development concept should be included in the design, construction and operation of buildings to conserve both the economic well-being and environmental health around the world. The research connected to sustainable lighting in school buildings presented in this paper is one of results of the SURE-BUILD project (Sustainable Redevelopment of Buildings in Poland) a project where scientists from the Norwegian University of Science and Technology and the Warsaw University of Technology cooperate to find the best solutions for sustainable redevelopment of buildings in Poland.. Principles of sustainable lighting design Recently, a sustainable approach to lighting design has been considered. This approach appreciates two well-known lighting concepts: energy efficiency and lighting quality. The principles of sustainable lighting design should be used in designing, construction and operation of lighting systems in buildings. The basic rules of sustainable lighting design are: - maximising the use of daylighting in interiors; - minimising the use of electric energy for lighting; - maintaining high quality of lighting, - using environmental friendly lighting equipment, that does not contain harmful substances or materials; - protecting wasted lamps (recycling). 1

2 3. Sustainable lighting solution in a primary school in Zgierz The primary school no. 1 in Zgierz near Lodz in Poland was chosen as a case for the SURE- BUILD project. The whole building envelope will be thermo-modernised and all technical systems i.e. heating, ventilation and lighting systems will be upgraded. It is agreed in the project group that cooling systems should not be an option for school buildings. Covering of the space between buildings A and C, figure 1, with a glazed roof is under consideration. 3.1 Description of the primary school in Zgierz The school consists of five two-floor buildings oriented east-west and connected by one-floor pavilions, figure 1. The main teaching areas, classrooms and laboratories, are situated in buildings A, D and C. Because of the limited size of this paper, the way sustainable lighting principles are to be implemented in the Zgierz school will be shown on the example of a typical classroom on the first floor in the building A. The same lighting principles will be used in nearly all interiors in the Zgierz school. Figure 1. The plan of the primary school no. 1 in Zgierz. 3. Daylighting in a typical classroom Sustainable approach exposes the usage of daylight as a primary light source of interiors. Daylight in classrooms is provided by windows that give the variety and variability of lighting and a view out. The daylight in a classroom has to give enough light level in periods of overcast sky and comfortable lighting conditions in periods of clear sky with sun conditions. Figure. The outside view of building A. Overcast sky As a part of the thermo-modernization of the building envelope all windows will be removed. This gives a possibility of reconsidering the size of the windows and their position in the window wall. The size of a glazing area in the classroom was calculated using the Leso Dial

3 program to meet the recommendations for minimum daylight factor (DF) that were formulated on the basis of the experience from daylighting studies in many schools in Norway [6][7]: The mean daylight factor in the classroom: DF mean > 4% The minimum daylight factor in the classroom: DF min > % For the daylighting calculations the area between the bearing walls articulated on facades as slightly sloped two-floor pillars, figure, was defined as a classroom. The classroom has today two large windows divided into smaller areas vertically and horizontally. The classroom has the dimensions: height 3.1 m, depth 5, m, width 6.8 m. The reflectances in the renovated classroom will be: floor 0,, wall 0,5, ceiling 0,7. The outdoor obstructions make 0º elevation angle; the outside obstructions and the ground have both reflectances of 0%. Two following glazing types were considered: 1. Two glass layers of energy saving and sun protecting glazing: Suncool HP Brilliant 66, Pilkington, U-value: 1,0 W/m K (if argon is used in the gap), total solar transmittance, TST: 34%, light transmittance T v = 66%. Two glass layers of energy saving glazing: Optitherm SN, Pilkington, U-value: 1,1 W/m K (argon), TST: 58%, light transmittance, T v =79% To meet the daylighting recommendations formulated above, the glazing type 1 should have an area of minimum 1,65 m, which is more than the existing glazing area and is about 36% of the floor area. If the transmittance of the glazing increases to 79%, type, the minimum glass area becomes 10,5 m, which is about 9% of the floor area. To avoid too large glazing area the project group decided to choose the glazing alternative no., but this decision will be revised after the energy and thermal comfort calculations for the whole school building will be finished. Clear sky with sun During the clear sky periods the sunlight should be actively used to illuminate the classroom. Since the illuminance due to the sun radiation is typically more than one magnitude higher than the illuminance from the overcast sky, the whole window glazing (if not shaded) will transmit much more sun radiation in sunny days than it is necessary for lighting purposes. The overheating can occur due to the infrared part of solar radiation, especially during spring and summer. Also solar glare can occur, especially for low solar angles. To avoid such problems a sun shading device is necessary. Placing the shading device on the outside of the glazing is the most effective way for preventing overheating. But if the sunshading system covers the whole glazing, the users typically close the whole sunlight outside, the mean illuminance level inside becomes too low and the electric light is switched on. The result is exactly opposite to the principles of sustainable design. To avoid this, a part of the glazing should transmit the sun radiation inside the room and distribute it in the interior in a way that ensures comfortable visual conditions. What is the minimum always transmitting glazing area that ensures the minimum illumination in the room during the clear sky conditions? To answer this question the calculations with the following assumptions were made: 1. The classroom is oriented south. The operation hours of the school building are 8 am - 3 pm. 3. The mean outside obstruction angle is 0º. 4. The minimum illuminance on the working plane is 300 lx. 5. The light transmittance of the glazing for the normal incidence angle is 79%, for incidence angles higher than 50 : 7% for 55 and 68% for All surfaces in the room are perfect diffusers. In figure 3 the area of the sun diagram corresponding to the operation hours of the school is coloured. The grey coloured area corresponds to the time period when the classroom windows are shaded by neighbouring buildings, the yellow coloured area represents the sun hours when sunlight might penetrate into the classroom. Let us consider a room with one large window. The lower part of the window is totally shaded by a shading system, the sunlight penetrates only through the upper part of the window. The total flux entering the room can be easily calculated if the glass area A gl of the uncovered part of the window and the solar illumination perpendicular to sunrays E p are known. Let us start with the calculation of incident angle v of a sun ray on the glass in terms of the altitude angle α and the azimuth angle β, figure 4: 3

4 arctg ( tg ) ( tg ) (1) Figure 3. Solar diagram for Zgierz. Figure 4. The sun ray s incidence angle on the window glass. Because the solar illumination depends on the incident angle: Egl E p cos and: E gl ()(3) A The light flux falling on the glass having the light transmission T v is: A T E cos( arctg ( tg ) ( tg ) ) (5) gl p Let us assume, that the light flux penetrating through the glazing falls on a perfectly diffuse surface and is evenly distributed in the room. The formula for calculation of the internally reflected component, Hopkinson, 3.5. [5], can be used to calculate the mean illuminance on the surfaces in the room, R Emean (6) Atot ( 1 R) where R is the mean diffuse reflectance of the room surfaces and A tot is the total area of room surfaces. The formulas 5 and 6 were used to calculate the minimum glazing area needed to ensure minimum 300 lx on the room surfaces. The results are presented in table. If the azimuth angle is limited to 50º, the minimum glazing area that ensures minimum 300lx on the room surfaces is 1,78 m. The 10,5 m window glass area could be divided in the following way: 8,7 m in the lower part, 1,78 m in the upper part. Table. The minimum glazing area that ensures minimum 300lx on the room surfaces in sunny days. Solar Altitude in degrees (º) Solar Azimuth (º) ,16 m 1,0 m 1,05 m 1,18 m 1,70 m 10 1,17 m 1,03 m 1,05 m 1,18 m 1,71 m 0 1, m 1,07 m 1,09 m 1,1 m 1,73 m 30 1,3 m 1,14 m 1,14 m 1,6 m 40 1,47 m 1,6 m 1,4 m 1,47 m 50 1,74 m 1,6 m 1,56 m 1,78 m 60,65 m,1 m,08 m In a classroom with naked windows the sunlight will fall on students and/or teachers, something that is recognized as uncomfortable. To avoid this, a sunlight redirecting system is necessary. We have chosen a specially designed Venetian blinds having a slightly curved (valley-form) horizontal blinds with a specular upper surface which have a very high reflectance (miro quality R>95%). The system reflects nearly all incoming sunlight to the ceiling, even if blinds are sloped a little. To maintain the high optical quality of the upper surface, the blinds should not be movable, but the slopping of the blinds should be adjustable to a degree necessary for redirecting all sunlight to the ceiling. 4 gl

5 The negative impact of a fixed system is the reduction of daylight level in the overcast sky periods. The studies of many different blind systems presented in [4] show that a blind system may reduce the daylight factor in the rear zone of the room by 0 40%. To examine how large reduction of diffuse daylight can be expected due to our system, the model of the classroom was made in 1:10 scale and a series of model measurements in the artificial sky in NTNU, Trondheim, were carried out. To better illustrate the impact of blinds, the measurements were carried out twice. In the first series the lower part of windows was uncovered, in the second it was covered by an opaque cardboard. The results show that the contribution from the upper part of the window is much more even than the contribution from the lower part. The obstruction of the diffuse daylight due to the specular blinds differ with the distance from the window wall. The obstruction is largest in points and 1 (respectively 45% and 36%), figure 5. In the rear zone, where the daylight factor is typically lowest, the reduction of daylight factor is only above 16%. In the point 5, situated vertically on the back wall over the door height, there is no reduction at all. To counteract the 16% reduction of daylight factor due to the specular blinds, the glass area in the upper part of the window has to be increased by 1/0.84 i.e. by 19%. The minimum area of a glazing equipped with specular Venetian blinds that ensures visual comfort and minimum illumination in the room during the clear sky conditions is.1m, about 6% of the floor area. Daylight factor on the working plane, clerestory window and view window DF 0,0 % 18,0 % 16,0 % 14,0 % 1,0 % 10,0 % 8,0 % 6,0 % 4,0 %,0 % 0,0 % distance from the window wall blinds no blinds, only clerestory window no blinds blinds, only clerestory window Figure 5. Vertical section through the classroom with measurement points to the left. Daylight factor measured in points 1-4 with and without blinds in the upper part of the windows, to the right. Figure 6. Penetration of sunlight into a classroom in summer and spring/autumn. The blinds in the upper part of the windows are placed horizontally. The window size and the division into lower and upper parts is not a result of this study. Conclusions for daylighting The windows are divided into a lower part which has a total area of 8.7 m, (4,5% of the floor area) and an upper part.1m (6% of the floor area). To ensure thermal and visual comfort in the room the lower part of the windows is equipped with an outside shading 5

6 system that is controlled automatically, i.e. the blinds move up if the sky is overcast, down if the sky is clear; the slopping of the blades is automatically adjusted to an optimal slopping that prevents direct sunshine and maintains as much outside view as possible. In periods without daylight the blinds are positioned vertically. They have a much higher reflection factor than the glazing (about 50%), something that contributes to better efficiency of the electric lighting system. In the upper part specially designed Venetian blinds with a specular upper surface, as described before, are used. They are not movable, but the slopping of the blinds can be slightly manually adjusted by the users. Figure 6 shows the sunlight distribution in the room with specular blinds oriented horizontally. In summer the sunlight is completely redirected to the ceiling. To redirect the sunlight to the ceiling in spring/autumn the blinds have to be slopped a little (this was difficult to do in the model). 4. Electric lighting in a typical classroom Quality of electric lighting in polish schools is unsatisfactory. The most common errors in polish classrooms were shown [8]. In our study electric lighting is considered as a supplementary light source in classrooms. Still, there are periods (mostly in winter time) when electric lighting is used as the only light source. Then, it should fulfil the requirements of standard PN-EN [1]. In classrooms of primary schools illumination levels on task areas shall not fall below 300 or 500 lx, depending on task or activity, UGR shall not exceed 19 and CRI shall not be lower than 80 table 3. In a typical polish classroom benches are located regularly, in two or three rows, covering all the floor area. Thus, in our case the task area is taken as the area between walls. Uniformity on the task area should be high, while the minimum to average illuminance shall not be lower than 0,7. In classrooms with DSE screens, luminance limits of luminaires which can be reflected in the screen shall not be exceeded according to the standard. Table 3. Lighting requirements in classrooms according to PN-EN [1]. Type of interior, task or activity E m UGR CRI [lx] Classrooms, tutorial rooms, music practice rooms, computer practice rooms (menu driven), language laboratory Classrooms for evening classes and adult education, practical rooms and laboratories, art rooms, blackboard and demonstration table General considerations It is intended to replace the old electric lighting equipment with a new energy efficient one in all classrooms. We expect to reduce the number of luminaires and total power installed (lower energy loads), and to provide high lighting quality in the school interiors. For each classroom a few options were considered. The main assumptions were as follows: - general lighting, regular lay out of luminaires; - ceiling mounted, louvre luminaires; - T5 fluorescent lamps with electronic ballasts. Lighting equipment In this paper four solutions are presented. First and second options are surface mounted direct lighting luminaires, third and fourth options are pendant mounted direct indirect lighting luminaires. For the first and third options luminaires with one T5 35W fluorescent lamp were selected (300 lx solutions). For the second and fourth options luminaires with two T5 35W lamps were selected (500 lx solutions). Louvres of selected luminaires are made of highly specular anodised aluminium to fulfil high discomfort glare restrictions and luminance limits in classrooms with DSE screens. In each option one additional blackboard luminaire (asymmetric distribution) with one T5 35W fluorescent lamp was necessary. 6

7 Maintenance Maintenance factors were estimated based on the agreed unified schedule for the all classrooms. It was decided that the environment was clean. For direct lighting, enclosed luminaires were selected, and for direct indirect lighting, luminaires with open top reflector. The maintenance schedule for the classrooms was as follows: - time between cleanings of classrooms: 4 years; - time between cleanings of luminaires: 1 year (the end of each summer holiday); - lamp replacement: Spot. The resulting maintenance factor for direct lighting was 0,80 and for direct indirect lighting was 0,75. Results In table 4 the results of calculations, with the use of the DIALux program, are presented. Four solutions for a typical classroom in the school are introduced. Existing lighting in the classroom is shown too. Results of existing lighting were calculated for evaluated maintenance factor because illuminance levels varied between classrooms, as there were no maintenance procedures executed in the school. Table 4. Lighting solutions and existing lighting in a typical classroom of the primary school no.1 in Zgierz, Poland. Existing lighting Solution lx direct Solution 500 lx direct Solution lx direct indirect Solution lx direct indirect Bare lamp batten luminaires Surface mounted Conventional ballasts T1 lamp 40W Flux: 500 lm CCT: 6500 K CRI: 70 Regular: 5x3 Louvre luminaires Enclosed Surface mounted; direct lighting Electronic ballasts Regular: 5x+1 T5 lamp 35W Luminous flux: 3300 lm CCT: 4000 K CRI: 85 Regular: 4x+1 Louvre luminaires Open top reflector Pendant mounted; direct indirect light. (suspension height 0,5 m) Electronic ballasts Regular: 6x+1 Regular: 5x+1 Power: 1350W 4,96 W/m E m =605 lx MF=0,70 4,13W/m /100lx UGR=5 E ceil /E=0,95 E wall /E=0,75 Lighting control: Switching Manual, ordinary wall-box switches Power: 390W (49W*) 7,1 W/m (8,53 W/m *) E m =345 lx MF=0,80,09W/m /100lx UGR=19 E ceil /E=0,3 E wall /E=0,40 Power: 64W (663W*) 11,54 W/m (13,18 W/m *) E m =547 lx MF=0,80,11W/m /100lx UGR=19 E ceil /E=0,35 E wall /E=0,35 Power: 468W (507W*) 8,65 W/m (10,08 W/m *) E m =39 lx MF=0,75,63W/m /100lx UGR=16 E ceil /E=1,00 E wall /E=0,47 Lighting control: Switching Day switch plan circuits controlled independently Power: 780W (819W*) 14,4 W/m (16,8 W/m *) E m = 531 lx MF=0,75,7W/m /100lx UGR=16 E ceil /E=0,96 E wall /E=0,45 * - values include blackboard luminaire A blackboard luminaire in each solution guarantees the illuminance being higher than 500 lx and uniformity higher than 0,7 on a blackboard. The direct lighting solutions fulfil the basic requirements of the standard (illuminance level, uniformity, discomfort glare and colour rendering index limits) providing energy efficiency. 7

8 The direct indirect lighting solutions are less energy efficient but provide better lighting quality (better glare limitation and ceiling illumination) and better visual appearance too. Solutions 3 and 4 are suggested as preferable in our case. Solution 3 should be selected for a classroom where 300 lx requirement is applied and solution 4 should be selected for a classroom where 500 lx requirement is applied. The final selection of the lighting solution for each classroom will be examined, including cost analysis. Due to high energy efficiency of our electric lighting solution both the decrease of amount of electricity consumed and the decrease of environmental effects are expected. T5 fluorescent lamps selected in our solution have smaller tube diameter than T1 lamps used in existing lighting of the school. Reduction in diameter causes weight and size reduction and as a result reduction of materials (glass, fluorescent powder) and compounds mercury. Burn out lamps will be collected and transported to an authorised recycling company. 5. Conclusions The principles of sustainable lighting design were formulated and used in the lighting concept of the primary school no. 1 in Zgierz Poland. Because of its many advantages, both for the people and the environment, daylight is utilised as a primary light source. For overcast sky conditions the daylight factor calculations were made to find the minimum glazing area that secures a minimum daylight level in interiors. For clear sky with sun conditions the effort was made to: 1. assure the visual and thermal comfort for occupants by usage of the outside sunshading device over the most part of the window,. use sunlight as a light source, by defining a small upper part of the window as the always-light-transmitting part. The upper part is equipped with an internal daylighting system in form of specular blinds that redirect sunlight to a diffuse ceiling. The calculations have shown that for a typical classroom the upper part of the window should have an area of minimum 6% of the floor area; the lower part the area about 4,5% of the floor area. Importance of energy efficient electric lighting was included too. Application of modern electric lighting equipment will considerably reduce the installed power (over 50%) and the use of electric energy on lighting in the school. Effective use of electric lighting (planned maintenance and control program) should substantially reduce the total operating costs of the building too. New solutions will also secure much higher quality of electric lighting, something that will increase well-being and performance of students and teachers. Principles of sustainable lighting design should be disseminated to include lighting society in worldwide sustainable development process. Acknowledgments This paper is one of the results of the SURE-BUILD project financed by The Research Council of Norway and Norwegian Council for Higher Education. References [1] PN-EN , Light and lighting Lighting of work places Part 1: Indoor work places, PKN, Warsaw, 004. [] ANSI/IESNA RP-3-00, Lighting for Educational Facilities, New York, IESNA, 000. [3] CIBSE, Code for Lighting, Butterworth Heinemann, 00 [4] IEA Solar Heating & Cooling program Daylight in buildings. A source book on daylighting systems and components July 000. [5] Hopkinson, R.G. Peterbridge P., Longmore J. Daylighting, William Heinemann Ltd, London, [6] Matusiak Barbara, Aschehoug Øyvind, Daylighting Analysis for the Kvernhuset Lower Secondary School, Fredrikstad, Norway. Proceedings of The third ISES-Europe Solar Congress: EuroSun 000, 19- June, Copenhagen, Denmark. [7] Matusiak Barbara, Daylighting in the Kvernhuset Lower Secondary School, Fredrikstad, Norway. Proceedings of PLEA 000: Architecture, City, Environment. July 000, Cambridge, United Kingdom [8] Pracki Piotr, Lighting quality in schools Introductory study, 5 th Session of the CIE, San Diego, Proceedings Volume, CIE