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. We redid the calculation to compensate for the high outdoor illuminance on the day that we took measurements. If we use half of the measured outdoor illuminance, the equation yields a 95-ft2 skylight. We chose to consider a reasonable illuminance for an overcast day in Boston: 20,000 lux. Using this value, we obtain a skylight with an area of about 200 ft2. Therefore, we chose to make a skylight with dimensions (10 ft)*(20 ft) = 200 ft2.

Design Solutions: New Design of Skylight

The Shape:

Once we adjusted the size of the skylight to the new dimensions of 10’ x 20’, we looked into other facets of the design that could be utilized to improve the lighting conditions. Our first goal of bringing more daylight into the space will be achieved with the larger skylight. Next, it was necessary to study the environment and structures surrounding the lounge in order to decide where to place the new skylight. We have to work around the shadows cast by the surrounding buildings on the terrace outside the faculty dining area on the fourth floor of the Stata Center. To the north is the main tower of the building and to the southwest there is another large tower that masks sun penetration onto the terrace above our space. The first design of the skylight had the glass angled at 20 degrees from the horizontal facing the south to allow for more light during the winter months. This angle brought the glass closer to the normal of the winter light, however it did not reach the normal to the winter light. This is because having a skylight at a lower angle actually captures more diffuse light throughout the year, which is common to overcast climates like Boston. This design allows more daylight to penetrate into the space (Figure 6).

Image removed due to copyright restrictions.

Figure 6: Basic section cut through skylight, illustrating angle of glass

Unfortunately, due to the tower to the southwest of the terrace, much of the sunlight that we wanted to receive from that side will be blocked. Thus, we had to focus our angle towards the southeast and rely on the direct light earlier in the day to fill the space. Later in the day, we can use the reflections off of the surrounding buildings to get diffused light into the space. (Figure 7)

Figure 7: Section of skylight with slanted well above and below and potential integration into the terrace – South is left

In addition to altering the angle of the skylight, we propose slanting the walls above the skylight in order to reflect more direct light through the glass. The slanted walls allow us to avoid the current well structure of the skylight, while fitting in nicely with the existing architecture. (Figure 7) The light will reflect against the walls of the skylight and be directed into the space. The angled walls below the skylight direct the transmitted light deeper into the back of the space reducing the dependence on artificial light even in the back of the room.

Figure by MIT OpenCourseWare. Figure 8: Diagram showing new location and orientation of skylight (yellow box) The Glass: The larger area of the opening has the potential to dramatically increase the heat gains in the CSAIL Lounge. In order to protect the space from this side effect of our proposal, we researched the different possible glasses that could be used in this skylight. If money is not to be considered, we would like to use a special type of glazing that allows for maximum light transmitted and minimum solar heat gains. We found a new material called monolithic aerogel, which has been used as a glazing for double pane windows. Its ability to insulate against solar heat is unprecedented. It has a thermal constant of K=0.003 W/mK with a light transmittance of 0.84 – 0.87. It has a slight bluish tint against dark backgrounds and a white and translucent against bright backgrounds. (Figure 9) This material would be placed between the two panes of glass to achieve a highly insulated composite with an overall transmittance of about 0.7.

Photograph of aerogel shielding matches from flame removed due to copyright restrictions.

Figure 9: Illustration of aerogel ability to protect against heat transfer

Design Solutions: Advanced Fenestration System

The skylight will not transmit enough daylight into the space to reach the north side of the room where the lounging chairs are located. The skylight cannot be in the center of the room because there are more stories of the Stata Center located above the CSAIL lounge, and also the two story ceiling makes light penetration more difficult because it must travel further to illuminate the work plane. This truth led us to investigate other methods to allow daylight to enter the space. We had to limit ourselves to systems that could carry daylight from the roof to inside the space in an indirect way. This is because the space does not touch the exterior envelope anywhere except for where the skylight was placed, thus punching windows through the walls was not an option. The system that we found to make the most sense was a hybrid fenestration system consisting of anidolic zenithal collectors with light pipes and reflective scoops. Our goal is to carry daylight into the lower level of the space so that it would be more useable and so that less would be lost in transmission from the second floor. We want this light to be diffuse and simply increase the over illuminance of the space. The existing lounge has shelf lighting encased in an aluminum box along the wall beneath the balcony. (Figure 10) Though this light is intended to shine upward toward the underside of the balcony and then be reflected further into the space, it simply shines on the wall itself and most of the illuminance is lost to a volume of the space that is well above the work plane.

Figure 10: Electric lighting housed in aluminum shelf

Aesthetically, we want the fenestration system to achieve an ambiance similar to that found in the Musée De Grenoble in France. (Figure 11) Rather than covering the ceiling with this diffuse light however, it wraps around the room beneath the balcony. It would be similar in that the daylight is unexpected and does not seem to enter directly through a window or skylight. The system that we will discuss has never been implemented before, and the parts are not manufactured, thus the cost of our system would be phenomenal. Each piece would have to be custom designed and produced to fit the space. The existing space would also have to be heavily reconstructed in order to install the system. The first cost would probably not be worth the money saved in energy costs for a very long time, however it is interesting to consider such cutting edge technology in a new way. We hope that this technology will become more accessible to architects and become a viable option in our lifetime. Photograph removed due to copyright restrictions. Taken from Reference 1.

Figure 11: Inspiration – Musée De Grenoble – France1

The fenestration system we are proposing brings light from the roof to the underside of the second floor balcony. It does this in three steps: gathering the daylight, transporting the daylight, and releasing the daylight.

Gathering the Daylight:

To gather daylight, we are proposing a series of anidolic zenithal collector. (Figure 12) One reason for this is that anidolic systems are functional in overcast climates like Boston. Often anidolic systems are positioned to the north to avoid direct sunlight penetration into the space below. Since the mode of our daylight delivery is diffuse because the light ultimately bounces off of the underside of the balcony, we believe that our anidolic collectors could be pointed in any direction. Thus we will point the anidolic systems south in attempt to maximize light collection. These systems will be built around the skylight on the roof terrace, directly above the wall of the CSAIL lounge. An even more efficient mode of collection (though once again overly expensive for our project) would be to configure a heliostat to follow the path of the sun and control the position and angle of the anidolic collector accordingly to maximize light intake. There is also a chance that once installed this system may be sensitive enough to gather moonlight at night. Diagram removed due to copyright restrictions. Taken from Reference 2.

Figure 12: Schematic of Anidolic Zenithal Collector2

Transporting the Daylight:

In order to transport the light from the anidolic zenithal collector to beneath the balcony on the lower lever of the lounge, we suggest a series of light pipes. The light from each collector will be fed into a reflective light tube. The light tube surface will be coated with aluminized plastic that has a reflectance coefficient of 0.94. The tubes will run inside the existing walls of the lounge, and thus can be straight pipes. In order to minimize the amount of reflections and light loss in the transportation of the light, each light tube will be equipped with one set of collimating lenses right below the anidolic collector. Collimating lenses serve to gather light into parallel beams so that the light can be sent directly down the tube. (Figure 13) This is because collimating lenses have a focal point that approaches infinity. Though there will be losses in the transmittance of light through the glass lenses, this would be less than the amount of light lost due to the many reflections that would occur if the tube were left empty. Diagrams removed due to copyright restrictions. Taken from Reference 2.

Figure 13: Transporting the Light – Light pipes with collimating lenses2

Releasing the Light:

Our system to release the gathered light into the CSAIL lounge involves a light scoop that directs light to the underside of the balcony and then this light is diffused over the work plane. Because of the collimating lenses, the light enters the scoop vertically as seen in the top image of Figure 14. Light is then reflected by the scoop that is coated with a specular material like the aluminized plastic in the light pipe. Next, the light is reflected to the underside of the balcony and then spread deeply into the space. The values shown on this picture were calculated using the formulas:

a = a´ / sinθ and L = (a´ + a) cotθ, assuming that the scoop angle is thirty degrees. This angle is measured from the horizontal to the line drawn between the bottom of the entry aperture and the far edge of the upper reflecting surface. Diagram removed due to copyright restrictions. Taken from Reference 2.

Figure 14: Release of daylighting into the space2

Electric Lighting:

When daylight is not providing enough illuminance for the space, artificial light must be used. Using the fenestration system described earlier, we would like to provide electric lighting in such a way that the occupant of the room might think the space is still being illuminated from daylighting carried by the anidolic system. In order to achieve this goal, we would place electric lighting fixtures inside the scoop as shown in Figure 15. These fixtures would be equipped with a photoelectric dimming system because many people share the space and one person does not control the lighting. We will set a range of illuminance values that must be achieved at the work plane, and if the current value falls below that range then the control system would increase the power output of the artificial lighting of the scoop to meet the specified illuminance. If more daylight enters the space, the lights will dim accordingly in order to waste less power. Diagram removed due to copyright restrictions. Taken from Reference 2.

Figure 15: Location of artificial lighting in reflective scoop2

There will also be sensors throughout the room to detect occupancy. If the room is empty, then the artificial lights will be turned off until someone reenters the space. This ensures that power is not used to light an empty room. The artificial lighting that comes from the scoop, as well as that specified for task lighting will be full spectrum compact fluorescent bulbs. These have a color-rendering index of more than 91, where the color-rendering index of sunlight is 100. A 55W compact fluorescent bulb emits as much light as a 300W incandescent bulb and can last more than 8000 hours. (Figure 16)

Image removed due to copyright restrictions.

Figure 16: Full spectrum compact fluorescent bulb

Combining all of these elements, the fenestration is depicted schematically in Figure 17 and the entire design is depicted on the plan of the terrace in Figure 18. The impact of our additions to the lounge affect the terrace in a meaningful way, however the space is rarely used by patrons of the Stata Center, and we believe that with small architectural moves we can integrate our intervention into the landscape like the seating area depicted in Figure 7. Figure 17: Advanced fenestration system

Figure by MIT OpenCourseWare. Figure 18: Location of anidolic zenithal collectors – depicted in cyan Qualitative Improvements:

Overall our design allows the space to have less reliance on artificial light, which leads to a more efficient space when considering electrical energy consumed. The daylight penetrates deeper into the space because of the increased size of the skylight. The visual comfort is improved because we have removed the existing harsh fluorescents, and ideally have replaced them with our advanced fenestration system. If funds are to be taken into account however, replacing the existing lighting with full spectrum compact fluorescents definitely improves the color rendering of the space while providing a more even distribution of diffuse light. Though much of our design is not feasible at this time due to lack of the technology penetrating the market, increasing the skylight definitely achieves many of our design goals, and we hope that advanced fenestration systems will begin to become more commonplace and cost effective in the near future.

References

1 Fontoynont, Marc, Daylight Performance of Buildings, James and James Ltd., London, 1999.

2 Baker, Nick and Steemers, Koen, Daylight Design of Buildings, James and James Ltd., London, 2002.