DAYLIGHTING ANALYSIS FOR THE KVERNHUSET LOWER SECONDARY SCHOOL, FREDRIKSTAD, NORWAY

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1 DAYLIGHTING ANALYSIS FOR THE KVERNHUSET LOWER SECONDARY SCHOOL, FREDRIKSTAD, NORWAY Barbara Matusiak, Øyvind Aschehoug Faculty of Architecture, Planing and Fine Arts, Norwegian University of Science and Technology (NTNU) Alfred Getz vei 3, N-7491 Trondheim, Norway, Tel. No , Fa No The paper focuses on the method for daylighting analysis on the eample of a lower secondary school that is to be build in Fredrikstad in Norway in year Each of the departments of the educational area has rectangular shape oriented in east-vest direction with classrooms oriented to the north. The outside, northfacing walls are made of opaque wall elements, clear glass units (CG) and glazing units with ISOFLEX, a transparent isolation material, (IG). Daylighting simulations were carried for one classroom. Many alternative daylighting solutions were eamined, one with skylights placed in the south part of the classroom was chosen. Then the CG area and the IG area in the northfacing wall were calculated for different sizes of skylight in order to find a solution that gives high daylight levels and at the same time the highest possible energy saving potential. 1. INTRODUCTION The paper focuses on the method for daylighting analysis used during the design process of a lower secondary school that is to be build in Fredrikstad in Norway in year The school was designed by Pir II architects from Trondheim, who won an architectural competition for this school building. The architects were assisted by the authors with regard to daylighting. The school is to be built on ecological principles. The main objective of the project is to create a good indoor environment and at the same time aim at low energy consumption, natural cleaning of wastewater and recycling of building materials and components. Low energy consumption will be obtained by: Etended use of daylight and control system of electrical light Combined gravitational-mechanical ventilation Heat pump for heating In order to demonstrate ecological principles, the educational area is divided into three departments: blue, yellow and green, which symbolise ecological topics connected respectively to water, sun and greenery. Educational activities dedicated to each of those three topics will take place in the department that has the same name. 2. THE SITUATION The school is situated in Fredrikstad, a city in the southeast part of the country, that has decided on an environmental friendly profile. The site is located in the suburbs of the city. It is covered by a sparse pine forest, which will protect the school building from wind, dust and sound. There is a 3-5 m high drop in the terrain on the northwest part of the site, made by a long, steep, naked rock. Figure 1. The siteplan 3. DESIGN OF THE SCHOOL BUILDING The main design idea of the school building is based on the active use of the site qualities: the rock, the forest, and the light filtered by it. The ground floor of the building cuts into the rock. The blasted rock mass is further used to face the ground floor

2 of the building. In this way the rock rises again. This time it makes rectangular shapes oriented perpendicular to the rock direction. On the top of the rock there are three rectangular, long and narrow wings that almost float over the ground. Each of them has beautifully designed facades in an organic style, figure 2, and a slight strain of one of the colours: blue, yellow or green. They have very light epression that makes a strong contrast to the ground floor. The main entrance, formed as a glass bo, is situated on the ground floor. Workplaces for teachers, offices for administration staff, rooms for home economics, workshops, the school kitchen and the canteen are also placed here. The base educational areas are situated in the wings on the first floor. 4. DAYLIGHTING REQUIREMENTS The positive effects of daylight for health, wellbeing and productivity were the reason that all educational areas were defined to be dominated by daylight. Daylighting requirements were discussed with the client i.e. local authority for Fredrikstad, and architects who discussed them with the teachers. Daylight level The British CIBSE Code for interior lighting (1984) [1] gives a clear definition of daylight dominated area. If the electric lighting is not normally to be used during daytime hours, the average daylight factor should not be less that 5%. It is important that the distribution of light is even in the room or supplementary electric lighting may be required. If electric lighting is to be used during daytime the average daylight factor should not be less than 2%, if it is then the general appearance of the room will be of an electrically lit interior. The strongest requirements were set for the educational areas, see table 1. In order to secure sufficient daylight level for all pupils, the requirements refer not only to the mean daylight factor but to the minimum daylight factor in the room as well. Since the workplaces for teachers, which are to be used only few hours during the day, are architecturally integrated with the places for administration staff, the window design has to be the same in both those types of room. Daylighting requirements for this group of rooms are also equal and lower than for education areas, see table 1. Table 1. Requirements to daylight level. Average daylight factor Minimum daylight factor 2% 2% All education areas Gymnasium 5% 5% Workplaces for teachers 3% 1% Offices for the administration staff Secondary rooms (2%) - Table 2. The maimum luminance differences in a room. Maimum luminance differences Visual field/working field 3:1 Visual object/vdt 3:1 Visual object/surrounding 10:1 Maimum contrast in room 40:1 Glare Solar glare and any veiling reflections from the sunlight should not occur in the educational areas in the school, especially not on permanent work places. Luminance contrast It was recommended to follow IESNA RP-1 VDT Lighting Standard [2] as presented in table 2. Modelling The light in the educational areas should have such distribution that three dimensional objects shape and teture are clearly visible. Figure 2. Facades from the south

3 5. THE METHOD FOR DAYLIGHTING ANALYSIS The use of a simple daylighting simulation program enables one to carry out quite precise analysis of daylighting in a very short period of time. The method used for daylighting analysis was the same in all parts of the school: main educational areas workplaces for teachers and offices for administration staff rooms for home economics workshops gymnasium The results are presented only for the main educational areas. The method starts with evaluation of the daylight factor on a horizontal plane 80 cm over the floor level in a room representative for the respective part of the school. If the daylight level is lower than specified in the daylighting requirements, table no. 1, some alternative daylighting design solutions are proposed. Daylighting simulations are carried out by varying the most important parameters, i.e. size and placing of daylight apertures. The objective for parameter study for each alternative is to find the minimum glazing area that satisfy daylighting requirements specified before, and to find the optimal form and placing of the daylighting openings. The daylighting simulations were made using the LesoDial computer program [3]. communication area with entrances to the south. The area at the core was intended to be used for secondary rooms, such as cloakrooms and toilets, see figure 3 and 4. The original vertical section through the educational department, designed for the competition, show the daylighting strategy for classrooms, see figure 3. The northfacing wall with large, high, northfacing windows was thought to be the primary daylight source. The horizontal windows placed above the secondary rooms were thought to supplement daylight from the south. The northfacing wall was composed of three types of elements specified in table 3. The initial simulations showed that the secondary windows have very little effect on daylight levels. The roof over the south part of the building works as an overhang for those windows. The daylight factor in the south part of the classrooms was below 1%. It was necessary to improve the daylight level in this zone..north South Figure 3. The vertical section, department of education 6. DAYLIGHTING ANALYSIS The three educational buildings were originally designed with the main educational areas to the north and a Figure 4. Plan of the education building.

4 Table 3. Specification of the wall elements in the northfacing wall. Element Clear glass elements made of two layers of glass Elements with ISOFLEX, semitransparent material placed between glass layers Opaque wall elements made of light wood construction Light transmission factor τ Per cent of the wall area 76% 30% 36% 30% - 40% Parameter studies for each alternative were carried out to find the minimum glazing area that satisfy the daylighting requirements specified above, and to find the optimal form and placing of the additional daylighting openings in the room. The design of the northfacing wall was liked by architects very much. In simulations it was maintained for all alternatives. The reflection factors used in simulations were: floor 30%, walls 50%, ceiling 75%. The following alternatives were eamined (figure 5): 1. Small square skylights with ISOFLEX over the south part of the classroom, two skylights for each classroom. The skylights had a light transmission factor τ=44%. The idea of this alternative was to make additional openings in the building envelope just above the dark part of the classroom. 2. Vertical windows over the roof covering secondary rooms and the communication area. This alternative enables a view to the south and considerable penetration of sunlight. Solar shading is necessary. 3. Linear skylight with ISOFLEX over the south part of the classroom, the same idea as for the alternative 1. The daylight distribution in the south part of the classroom should be more even. 4. Linear skylight over the secondary rooms. This alternative was developed to combine the daylight aperture with ventilation duct that is situated below. The air in the duct could be preheated by solar radiation. 5. Clerestory over classroom oriented to the north. This alternative gives the most even daylighting distribution in the room. As the distance from the northfacing wall increases and the daylight level begins to be to drop, the clerestory gives additional light from the same direction and with the same colour temperature. 6. Clerestory over classroom oriented to the south. This alternative enables penetration of sunlight to the classroom. Sun shading is necessary only during the summer. At winter and spring/autumn the sunlight will be reflected/diffused by the sloped surface of the clerestory. Alternative 1 Alternative 2 Alternative 3 Alternative 4 Alternative 5 Alternative 6 Figure 5. The alternative solutions for daylighting in classrooms.

5 Table 4. The results of daylighting simulations in the classroom. Alt. No. Results Total glazing area (m 2 ) 1 Two small, square skylights, horizontal glazing with 4,50 ISOFLEX 1,5 1,5 m 2 Vertical glazing 1,2 8,4 10,08 3 Horizontal glazing with 5,88 ISOFLEX 0,8 8,4 4 Horizontal glazing 2,0 8,4 16,80 5 Vertical glazing 1,0 8,4 8,40 6 Vertical glazing 1,0 8,4 8,40 The alternatives 1 and 3 were most effective. Additionally they were simulated as a horizontal glazing with ISOFLEX material, something that considerably increases the insulation capacity of the glazing. Alternative 1 was the cheapest one, because it did not change the design of the building structure. The daylight requirements were satisfied by only two skylights, square in plan ( m), placed eactly over the poorly daylighted zone. The optimal placing of the skylights in the classroom was about 2,0 m centre distance from the south wall and about 2,0 m centre distance from the sidewalls. Alternative 1 was also preferred by architects. It causes the smallest changes in the overall architectural design. After alternative 1 was chosen, the design of skylights had to be adjusted to the design of the roof elements. The roof elements, placed perpendicularly to the building direction, could have up to 1.0m wide cuts placed along the elements centre line, see figure 4. This reduced the effect of the skylights. The easiest way to counteract was to remove ISOFLEX material from the skylights. A second parameter study was carried out to find how the size of the skylights influence the minimum size of the transparent part of the northfacing wall, i.e. clear glazing (CG) plus ISOFLEX glazing (IG). The transparent part of the wall was evaluated once as 50% CG and 50% IG, second time as 67% CG and 33% IG, see table 5. The evaluation criterium was the same: daylight requirements specified at the beginning of the design process. The results included in the table 5 were decisive for the architects in the further design process. The process is not finished yet. In the meantime, the skylights got another function. The HVAC consultant proposed to use them as an outlet for ehaust air. The net step in the design process will be devoted to solar glare control and possibilities to control luminance contrast in the classrooms. Table 5. The total area of the transparent part (CG+IG) as per cent of the northfacing wall area. Per cent of the transparent part of the northfacing wall (%) Skylight dimension (m) 50% IG 50% CG Average light transmission of the transparent part 0,56 33% IG 67% CG Average light transmission of the transparent part 0,63 A 1,0 1, B 1,0 1, C 1,0 1, D 1,0 1, E 1,0 2, ENERGY SAVING All solutions presented in table 5 gives high daylighting levels in the classroom. In order to find the alternative that has the highest potential for energy saving, the glazing area for each glazing element should be multiplied by its heat transfer coefficient U. The sum of areas of all glazing elements multiplied by the U value can be calculated for each alternative. The alternative, that has lowest U*A, has the highest potential for energy saving. In this project the sloped, nearly horizontal glass used in skylights has about 15% higher U-value than the vertical glass. The U-value for element with ISOFLEX is about 33% of the value for clear glass element. The total glazing area in the northfacing wall is equal 30m 2. The symbols used in tables 6 and 7: area of skylights (two skylights per classroom) area of clear glass units in the northfacing wall area of glass units with ISOFLEX material in the northfacing wall U SK = 2.3 W/m 2 K U CG = 2.0 W/m 2 K U IG = 0,7 W/m 2 K Table 6. Calculation of the sum of the U*A for the respective units. 50% CG - 50% IG in the transparent part of the northfacing wall. U SK U CG U IG UA A 2,0 4,6 11,6 23,1 11,6 8,09 35,8 B 2,4 5,52 10,8 21,6 10,8 7,56 34,7 C 3,0 6,9 10,2 20,4 10,2 7,14 34,4 D 3,6 8,28 9,30 18,6 9,30 6,51 33,4 E 4,0 9,2 9,00 18,0 9,00 6,3 33,5

6 Table 7. Calculation of the sum of the U*A for the respective units. 67% CG - 33% IG in the transparent part of the northfacing wall. U SK U CG U IG UA A 2,0 4,6 13,6 27,2 6,8 4,76 36,5 B 2,4 5,52 12,8 25,6 6,4 4,48 35,6 C 3,0 6,9 11,8 23,6 5,9 4,13 34,7 D 3,6 8,28 11,0 22,0 5,5 3,85 34,1 E 4,0 9,2 10,4 20,8 5,2 3,64 33,6 The results presented in tables 6 and 7 show, that the serie with 50% CG, 50% IG in the transparent part of the nortfacing wall, table 6, gives lower UA than the series: 67% CG - 33% IG, table 7, for all alternatives (A- E) and the differece is largest for alternative A, (smallest skylights). The lowest UA is to be find for alt. D and E, in the series: 50% CG - 50% IG and for alt. E in the series: 67% CG - 33% IG. REFERENCES 1. IES 1993 American National Standard Practice for Office Lighting, ANSI/IESNA RP , Illumanating Engineering Society of North America, New York, NY. 2. CIBSE Code for interior lighting (1994) ISBN Paule B. Bodart M. Citherlet S. Scartezzini J.L. Leso- DIAL Daylighting Design Software, In Proceedings of: Daylighting'98, May 11-13, Ottawa, Canada, Matusiak B. Daylighting in the Kvernhuset Lower Secondary School, Fredrikstad, Norway, In Proceedings of the Millennium Conference on Passive and Low Energy Architecture PLEA 2000, 2 nd -5 th July 2000, Cambridge, England. 8. CONCLUSIONS The glazing has usually many times poorer thermal insulation capability than all other elements in the building envelope. As a consequence it causes the highest energy losses during the year. In the first stage of a design process, when there is no time to make a comprehensive thermal analysis of the building, the smallest U*A for the respective glazing elements can be used as a criterium for choice of an alternative that has the highest energy saving potential. The method presented in this paper allows one to find solutions that balance the contradictory objections: requirements for high daylight level on one side and good thermal insulation on the other side. As the glazing is also the most epensive part of the building envelope, the method helps to reduce the investment coasts. 9. ACKNOWLEDGEMENTS This work has been supported by the Municipality of Fredrikstad, and The Norwegian Green Management Programme (GRIP)