Daylighting Analysis and Proposal for the CSAIL Lounge on the Second Floor of the Stata Center Elizabeth Katcoff Terianne Hall Megan Arp December 12th, 2006 Introduction: Description of the Space The CSAIL lounge is located on the 2nd floor of the Stata Center in the center of the building. The space is used for both relaxing and working. However, we noticed that lighting in the space seems inadequate to perform work without straining the eyes. Therefore, we wanted to analyze the space to identify the problems with the current lighting situation, determine how the lighting could be improved, and propose a feasible lighting design to correct the current situation. Figure by MIT OpenCourseWare. Figure 1: Plan of the space with current skylight in blue box (North is up) The rectangular space measures approximately thirty by sixty feet, with a short side facing south. On three sides of the room, a balcony extends five feet into the space. In addition, a staircase comes down from the balcony, with offices surrounding the space. The offices, lit by artificial light, allow light to leak into the space through large glass windows. Figures 2a (left) and 2b (right): Pictures of the Space. Picture 2a depicts a workspace on the south end of the room that faces the offices. Picture 2b provides a broader view of the lounge space, highlighting key elements such as the staircase and the artificial fluorescent lights hanging from the ceiling. The only natural light in the space comes from a nine feet by nine feet skylight in the southeastern corner of the room. The skylight is raised above the ceiling with light well that is seven feet deep. This decreases the amount of light that enters the lounge space. Although the skylight is rotated toward the portion of the building where there are no obstructions from the Stata Center’s towers, this does not change the amount of natural light entering the room because the skylight is not angled. Figure 3: The Skylight. From the figure you can see that the skylight is extremely small compared to the size of the space. The skylight’s deep light well and its location in the corner two floors above the space contributes to its inability to fill the room with natural light. Analysis of Existing Light Quality In September we measured the illuminance levels in the room on a sunny day. These readings provided a good indication of the lighting levels in the room for such a day. Around the balcony the readings were at a reasonable level for basic circulation. Directly underneath the skylight, the level of illumination was 165 lux. As we moved away from the skylight the levels dropped dramatically. About fifteen feet away from the skylight, the illumination level was 59 lux. (Figure 5) The illumination levels in the lounge below the skylight were well below those accepted for reading and writing. Directly under the skylight and next to the worktables the level of illuminance was 115 lux. At the tables themselves, where most students do their work, the illumination levels were 99 and 93 lux respectively. As we moved toward the back of the space and further from the skylight, the illumination levels continued to decrease. All of the measurements were taken at level of the work plane, which was defined as three feet above the ground plane. We chose these values to obtain an accurate measure of how much light was available to students working in the lounge. Since it was impossible to evaluate the space without the contribution from the artificial lights overhead and from adjacent offices, the illuminance measurements are a combination of natural and artificial light in the space. The low illuminance values found in positions further away from the skylight were probably from the artificial lights in the adjacent offices and conference rooms. Even with the artificial lighting, the illuminance in the space was well below the illuminance required to complete most tasks. Figure 4: Illuminance levels on work plane on sunny day where skylight is above the upper left corner of the picture (measurements are taken in lux) 142 72 59 165 Illuminance readings on ground plane of second level Figure by MIT OpenCourseWare. Figure 5: Illuminance levels for the balcony on a sunny day (measurements are taken in lux) Design Concept: Goals of Daylighting Improvements Before we designed a proposal to improve the light quality in the room, we outlined our objectives. Specifically, we wanted identify what improvements needed to be made in the space and we wanted to determine the best way to rectify the problems that were identified. First, we want a higher general illuminance in the space. For the lounge space, we want an illuminance level of 200-250 lux. In order to achieve this illuminance, the orientation of the chairs must be shifted to prevent light from the skylight from shining directly into the occupant’s eyes. For the table workspace, we would like to achieve an illuminance of 350-450 lux. In order to reduce glare on the work surface, we want to keep direct sunlight away from worktables. Knowing that it is impossible to reduce the glare at all times of the day, we defined our goal as: the prevention of glare on the work surfaces for 70% of the day. Another priority was to keep even lighting levels throughout the space in order to minimize eyestrain. We defined minimal eyestrain as a variation less than or equal to 200 lux throughout the room. We would also like to maximize the use of diffuse and indirect light, so that diffuse and indirect daylight contributes at least fifty percent of the illuminance during the daylight hours. This will provide better color rendering in the space. The use of artificial lighting should be reduced to half of its current usage. Furthermore, the artificial lights should have a high color-rendering index, unlike the current fluorescents lamps. Ideally, we would like a color-rendering index of more than 70. Visual comfort on the whiteboard on the western side of the room is also important. Once again, we’d like to minimize the direct light from the skylight that reaches the whiteboard in order to reduce glare. A glare index of less than 16 by the UGB standards would be preferable. There should be a minimum of 300 lux on the whiteboard so that the viewers can see it. In addition, there should be a minimum of a 6:1 contrast level between the ink on the whiteboard and the surrounding whiteboard so that the writing can be clearly seen by occupants at different angles to the whiteboard. In summation, we would like to penetrate diffuse light deeper into the space. We want to limit the light losses between the outdoors and the work plane so that more light can reach where it is actually used rather than only reaching the upper walkway where it is not needed. Design Solutions: Larger Area of Skylight In order to bring more light into the space, the first thing we needed to do was increase the size of the skylight. In order to determine the size of the new window, we used the following equation: Ewp=Eh* As/Awp*CU*T*LLF Each of the terms in the equation is defined below: • LLF is the light loss factor, which describes compensates for the future dirt on the wall and the floor. Since our room is well maintained and will be repainted often, there will be no future dirt on the walls, and therefore, there is an LLF of 1. • T is the net transmissivity of the skylight. This depends on the surface covers of the skylight, and what percentage of the light it lets through. Since we want to let in diffuse light, we are choosing a glass with an overall transmissivity of 0.7. • CU is the coefficient of utilization, which differs depending on the shape of the room and the reflectance of the surfaces inside it. The reflectance of the floor was calculated to be 0.12. The reflectance of the walls was calculated to be 0.43. The reflectance of the ceiling was calculated to be 0.5. The room cavity ratio is CR= 5h(l+w)/(lw). In this room it equals 5. Therefore the coefficient of utilization is 0.943. • Eh is the horizontal irradiance. This changes throughout the year. We used our measurement taken at 12:30pm in September. This is 84,500 lux. • Ewp is the Illuminance desired on the work plane. This is 350 lux. • Awp is the area of the work plane. This is the size of the space since the light will scatter throughout the space. Therefore, it is ~30*60=1800ft2. Using this calculation we determined a necessary skylight area of 47.5ft2. This is half the size of the current window. Several assumptions we made yielded a smaller skylight area than the desired, larger skylight area. First, the calculation did not take into account the depth of the room and the fact that the light needs to penetrate two floors. Furthermore, we did not take into account that the skylight could not be centered in the room and must be above the south side of the space. In addition, the equation does not take into account that the existing skylight has a deep light well. Moreover, the outdoor illuminance is based on a sunny day in September and does not take into account the illuminance level that would be measured on a cloudy day in the winter. In our initial calculation, we oversimplified the problem.