Bank of America / 19th floor preliminary analysis
contents contextual analysis direct solar solar exposure conclusions reflected sunlight conclusions
unc charlotte
lighting + energy technology laboratory
5 11 17 19 25
parametric analysis existing conditions
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visual comfort HDR introduction glare assessment
31 33
light shelf introduction false color iso-contour
37 39 41
performance conclusion
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parametric analysis uniform sky daylighting cross section
45 47
conclusions 19th floor preliminary analysis
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Analysis of the sun made the most logical start, as its effects can be seen on both the exterior and interior of the tower. Understanding how the urban context and the orientation manipulate that effect is key.
image 1.1
Hourly analysis of the equinoxes and both winter and summer solstices was conducted on the 19th floor. The analysis was completed using Ecotect. Preliminary work entailed constructing a digital model of the tower, 19th floor, and the adjacent urban context.
contextual analysis / direct solar
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8:00 am
10:00 am
figure 1.2
figure 1.3
summer solstice [dst] sun patch depth line
equinoxes
winter solstice
12:00 pm figure 1.4
These bi-hourly composites of the three main solar conditions begin to indicate solar movement trends within the span of the day. The low angle of the rising sun in addition to sparse exterior context allow large amounts of sun penetration in the morning from the east. The Hearst Tower does block a sizable amount of light during this time year round.
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2:00 pm figure 1.5
4:00 pm figure 1.6
At noon, very little solar penetration occurs both due to high sun angles during the summer solstice and equinoxes and the height of the proposed 210 Trade tower, which blocks the lower sun during the winter solstice. Afternoon penetration is relatively low again due mainly to denser exterior context blocking the setting sun.
6:00 pm figure 1.7
/ direct solar
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8:00 am
10:00 am
summer solstice [dst] figures 1.8 - 1.13
equinoxes figures 1.14 - 1.19
winter solstice figures 1.20 - 1.23
“View from the sun� images can provide a clearer understanding of how the context begins to affect solar conditions. During the summer solstice morning sun is nearly completely obstructed by the adjacent Hearst Tower. Evening penetration is eventually obstructed by the Interstate Tower and Independence Square.
At the equinoxes, the Hearst Tower blocks a smaller portion of the sun in the morning, allowing a high amount of penetration. In the afternoon, the Bank of America Plaza blocks the setting sun briefly before it falls behind the Interstate Tower.
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12:00 pm
2:00 pm
At the winter solstice, the 19th floor receives high solar penetration throughout the day. It should be noted that it is blocked for large durations of time by the proposed 210 Trade tower and the Bank of America Plaza.
4:00 pm
6:00 pm
/ direct solar
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First Citizens Interstate Tower Bank of America Plaza Independence Square
Omni Hotel
The Avenue
IJL Tower 210 Trade / Epicenter
Hearst Tower image 1.24
Building on the previous analysis, this seeks to explore the solar exposure time ranges for each of the 4 main facades. This includes discovery of the times other buildings interact with these ranges. The image above is a color key for the next 4 pages of diagrams.
contextual analysis / solar exposure
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Orthographic projection of seasonal sun paths as viewed from the NE facade.
receives exposure
not exposed
2 pm
12 pm
4 pm
10 am 6 pm
win
lstice
er so
s
2.5 hours from approx. [blocked by Hearst Tower] 9:30 - 12 3.5 hours from approx. [blocked by Hearst Tower] 8:30 - 12 2 hours from approx. [blocked by Hearst Tower] 9 – 11
noxe
ice olst
summer: fall/spring: winter:
equi
s ter
receives direct solar exposure in the early morning
summ
8 am
figure 1.25
13
Orthographic projection of seasonal sun paths as viewed from the SE facade.
receives exposure
not exposed
2 pm
12 pm
4 pm
10 am 6 pm
win
lstice
5 hours from approx. [blocked by Hearst Tower] 8:30 – 1:30 8.5 hours from approx. 8 – 4:30 6 hours from approx. 9 – 12:30 [blocked by 210 Trade] 1:30 – 5
er so
ice olst
summer: fall/spring: winter:
s noxe equi
s ter
receives direct solar exposure in the morning to midday
summ
8 am
figure 1.26
/ solar exposure
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Orthographic projection of seasonal sun paths as viewed from the SW facade.
not exposed
receives exposure
2 pm
12 pm
4 pm
10 am 6 pm
lstice
5.5 hours from approx. 12 – 5:30 5 hours from approx. 11:30 – 4 [blocked by BofA Plaza] 6 – 6:30 4 hours from approx. 10 – 11 [blocked by 210 Trade] 1 – 4
er so
e
lstic
r so
summer: fall/spring: winter:
s noxe equi
te win
receives direct solar exposure in the afternoon and evening
summ
8 am
figure 1.27
15
Orthographic projection of seasonal sun paths as viewed from the NW facade.
not exposed
receives exposure
2 pm
12 pm
4 pm
10 am 6 pm
win
lstice
er so
s
3.5 hours from approx. 1:30 – 5 2.5 hours from approx. 4:30 – 7 30 minutes from approx. 5:30 - 6
noxe
ice olst
summer: fall/spring: winter:
equi
s ter
receives direct solar exposure in the later afternoon and evening
summ
8 am
figure 1.28
/ solar exposure
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4 1 3.5 1.5
3 Based on direct solar penetration analysis, the most logical conclusion reached in reaction to it is to split the floor into zones. This would allow the possibility of not only activities to be distributed throughout the floor based on what time sun impacts the zone, but it also could be used to influence orientation of the interior furnishings and the subsequently required artificial lighting zones.
2 2.5 figure 1.29
contextual analysis / conclusions
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image 2.1
image 2.2
Upon visiting the 19th floor and witnessing the phenomenon seen in images 2.1 ad 2.2, it became clear that reflections off of adjacent structures will impact the visual comfort of spaces on this floor. These reflections can be modeled digitally, and using the context model developed for the direct solar analysis, the reality of the condition can be assessed.
figure 2.4
figure 2.3
contextual analysis / reflected sunlight
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Independence Square figure 2.5
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Bank of America Plaza
Independence Square
Hearst Tower
figure 2.6
figure 2.7
figure 2.8
It can be shown that direct sunlight will be reflected off three buildings surrounding the Bank of America Corporate Center and enter the 19th floor during the morning to early afternoon hours of the fall, winter and spring seasons. During the summer months the altitude of the sun is much greater and little, if any reflected light will enter the 19th floor. The three buildings are the Hearst Tower, Bank of America Plaza and Independence Square. This analysis at this time assumed the facades of these buildings to be entirely specular and did not account for diffuse surfaces.
/ reflected sunlight
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8:00 - 10:00 am
10:00 am - 12:00 pm
figure 2.9
figure 2.10
summer solstice [dst] sun patch depth line
equinoxes
winter solstice
12:00 - 2:00 pm
figure 2.11
The overall magnitude of reflected light, the result of our assessment is illustrated in the following three images which show reflected sunlight patches entering the 19th floor from the three identified buildings for both the equinoxes and winter solstice dates. Each image shows the extent of penetration for a two hour time period: morning (8:00 am to 10:00 am), mid-morning (10:00 am to 12:00pm) and early afternoon (12:00 pm to 2:00 pm). The depth of penetration changes by season and is identified by color.
/ reflected sunlight
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4 1 3.5
inner
figure 2.12
1.5
Maximum penetration composite
3 Based on direct solar penetration analysis and the reflected sunlight analysis, it becomes clear that there are two distinct zones within this floor: an inner and outer. The inner zone isn’t affected by direct solar or reflected sunlight at any time during the year, while the outer is.
2 2.5
outer figure 2.13
contextual analysis / reflected sunlight - conclusions
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figure 3.1 figure 3.2
The analysis of the southeast quadrant of the tower was performed over a 6 day period under mostly cloudy sky conditions. When compiled and analyzed, the graph above was constructed to represent the average foot candle value sectionally per time period. Converting this data to a sectional graph alludes to the availability of light up to 18 feet into the space with the most light available roughly 7 feet from the window wall. The first 3 feet from the window wall is a dark zone due to the size and depth of the columns. This creates a poor contrast condition for anyone looking towards the window wall, but there is sufficient amounts of daylight to perform any office activity.
figure 3.3
parametric analysis / existing conditions
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figure 3.4
logged data assessment - clear sky condition (5 day avg) A range between 30fc and 50fc was established a value of illumination. The data shows that the remains well above the set limits until 18 feet into the space.
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figure 3.5
figure 3.6
logged data assessment - overcast sky condition (7 day avg)
logged data assessment - worst case scenario
A range between 30fc and 50fc was established a value of illumination. The data shows that the remains well above the set limits until 15 feet into the space.
A range between 30fc and 50fc was established a value of illumination. The data shows that the remains well above the set limits until 18 feet into the space but drops below.
/ existing conditions
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figure 4.1: example of image sequence for combined HDR image
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figure 4.2: example HDR image
figure 4.3: false color analysis image
The following analysis was done using High Dynamic Range (HDR) photography. Multiple exposure images were taken on the 19th floor and within a scale model of the 19th floor while in the uniform sky (fig. 4.1). These images were then imported into the HDR image builder program Photosphere to create a single HDR image with valid surface luminance values (fig. 4.2). From this HDR image both false color and iso-contour analyses images were created. In the false color images, false colors are used to represent surface luminance values (blue tones represent dark surfaces and red tones bright surfaces) (fig. 4.3). These values are expressed in footlamberts. The iso-contour images include lines of equal luminance values in equal steps from zero to the maximum luminance value (fig. 4.4).
figure 4.4: iso-contour analysis image
visual comfort / HDR introduction
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figure 4.5: color-coded scale
figure 4.6: north corner
figure 4.7: southeast Wall
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Glare is a sensation caused by light in the field of view that is brighter than the level of light to which the eyes are adapted. This causes the eye to continually adjust and can create annoyance and discomfort. As a rule of thumb discomfort glare occurs on any surface in the field of view greater than three times the luminance level to which your eyes are adjusted. Key locations where chosen for example images taken on October 13, 2005 between 12:00 pm and 2:00 pm under partly cloudy skies on the 19th floor of the Bank of America Corporate Center. A 10mm wide-angle lens was used. This lens has a similar field of view as the human eye. Images were taken perpendicular to the main southeast window wall (fig. 4.7) and at the north and south corners looking outward (fig. 4.6 and 4.8). The following false color images were produced from the original images. Here false colors are used to define luminance values of surfaces within the visual field of the camera. A color-coded scale identifies luminance values assigned to specific colors (fig. 4.5).
figure 4.8: south corner
/ glare assessment
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figure 4.9: north corner, glaring surfaces shown in color
figure 4.10: southeast wall, glaring surfaces shown in color
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An average interior luminance was established by observing each image. From this a glare threshold of three times the established value was derived from a common luminance ratio rule-of-thumb. Surfaces brighter than this glare threshold are show isolated in figs. 4.9, 4.10 and 4.11. It is important to note that this analysis highlights only one moment in time. The external luminance environment and sky vault are constantly changing due to the diurnal and annual apparent movement of the sun and also changing weather conditions. This has a dynamic impact on the interior luminance environment. The position of the sun in the sky vault and potential reflected light from specular and highly reflective surfaces of surrounding building envelopes are also sources of glare and point to the need for further study.
figure 4.11: south corner, glaring surfaces shown in color
It is shown that visual comfort may be compromised by bright exterior building facades (fig. 4.11); however, the surrounding clear sky vault is the predominate source of glare, as seen is figs. 4.9, 4.10 and 4.11. To minimize the potential for visual discomfort, exterior glare must be dealt with at the window plane. Two control devices are suggested: automated shade screens for the lower view portion of the window and light shelves above the view window. The following analysis assesses the performance of different light shelf possibilities.
/ glare assessment
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This analysis as done using a scale model of the 19th floor in the uniform sky simulating overcast sky conditions. It compares the relative difference of interior luminance distribution and visual comfort within the camera’s field of view. The camera’s position was 25 scaled feet perpendicular from a typical window on the 19th floor of the Bank of America Corporate Center. A 10mm lens was used. Four window configurations are compared; no light shelf, a horizontal light shelf, a light shelf with its top tilted inward and a light shelf with its bottom tilted
inward. The dimensions of each configuration are given within its analysis. Two images where created for each light shelf configuration. The first set of false color images are helpful for assessing glare (visual comfort) because areas of greatest brightness are show by red tones and indicate potential glaring surfaces. The second set of iso-contour images are helpful for assessing internal illuminance performance (daylighting). The relative increase in depth of equal luminance lines can easily be compared between different light shelf configurations. To aid in this comparison a scale grid has been placed on the floor of the iso-contour images and the luminance value line of 10 footlamberts has been highlighted with a solid red line in each image. When comparing these light shelf configurations two performance criteria are important: daylighting and visual comfort. Simply put, the goal is to maximize the amount of light to space (daylighting illumination) while minimizing the potential for glare (visual comfort). This analysis model was built at a scale of 1” = 1’ and represents an ideal scenario of an interior luminance environment. Approximately 80% reflective flat white paint was applied to all interior surfaces; therefore, luminance values shown do not represent absolute values, which are dependent on actual internal
figure 5.1
light shelf / introduction
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fig. 5.2: no light shelf
fig. 5.3: light shelf: horizontal
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fig. 5.4: light shelf: top tilted inward
/ false color fig. 5.5: light shelf: bottom tilted inward
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fig. 5.6: no light shelf
fig. 5.7: light shelf: horizontal
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fig. 5.8: light shelf: top tilted inward
/ iso-contour fig. 5.9: light shelf: bottom tilted inward
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fig. 5.10
fig. 5.11
no light shelf
light shelf: horizontal
This configuration provided the space with the most illumination; however, it was uncontrolled. Fig. 5.2 shows that this configuration created the largest area of glare of all configurations and therefore performance poorest relative to visual comfort.
Fig. 5.3 shows this configuration reduced the potential for glare second best. Its daylighting performance was lower than that of the light shelf: top tilted inward configuration.
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fig. 5.12
fig. 5.13
light shelf: top tilted inward
light shelf: bottom tilted inward
This configuration reduced the potential for glare (Fig. 5.4). Its daylighting performance was second best.
It is clear from Fig. 5.5 that this configuration reduced the potential for glare far more than the others. However, its daylighting performance was well below all other configurations.
light shelf / performance conclusion
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figure 6.1
figure 6.2
40% Floor Reflectance
No Interior Reflectance
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figure 6.3 & 6.4
main / corner cross section (no reflectivity)
The analysis of a typical floor space was done simulating overcast sky conditions with no interior reflectance added (plan- fig. 6.2 and sections- figs. 6.3 & 6.4). The difference in amount of glazing indicated that a section should be taken though both the main office space and any of the four corners. In fig. 6.3 through 6.6, the top numbers represent the amount of daylight without the VLT of glazing factored in, while the bottom numbers represent the amount of light based on the current 22% VLT of the existing glazing components. The main section does not recieve sufficient amounts of daylight while the corner space does. A similar analysis was done using a floor with a reflectance of 40% (plan- fig. 6.1 and sections- figs. 6.5 & 6.6). The main section’s numbers dropped well below sufficient levels at 12 feet from the wall. This analysis points towards the several possible changes: use of a higher VLT glazing, modification of interior reflectances and/or inclusion of light shelves.
figure 6.5 & 6.6
main / corner cross section (40% floor reflectivity)
parametric analysis / uniform sky
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fig. 6.7
22% VLT glass average daylight factor between window wall and 15’ depth: no light shelf light shelf: horizontal light shelf: top tilted inward light shelf: bottom tilted inward
1.80 1.60 1.65 1.43
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fig. 6.8
70% VLT glass average daylight factor between window wall and 15’ depth: no light shelf light shelf: horizontal light shelf: top tilted inward light shelf: bottom tilted inward
6.03 5.08 5.25 4.55
/ daylighting cross section
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The proceeding analysis has intentionally divided the spectrum of daylighting issues on the 19th floor into five primary areas of concern:
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•the impact of direct solar penetration
1
•the impact of glass VLT on daylighting performance •the impact of ambient contextual sources of reflected light •the assessment of contrast in the space relative to impacts from sky, external and internal sources of luminance
3.5
inner
1.5
•existing and model daylight penetration
3
2
outer
2.5 figure 7.1
final conclusions / 19th floor preliminary analysis
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The following recommendations are made considering the synthesis of these issues. 1. Activity Zoning There are two zones created from this analysis: a perimeter zone impacted by direct and reflect sunlight and an interior zone (fig. 2.13). The off cardinal rotation of the building’s floor plate coupled with the impact of reflected light off of the ambient context can cause both heat gain and glare on working surfaces. This issue will also affect vertical surfaces as seen from across the space. These forces are not static and should inform the programmatic uses of these zones, possibly through the consideration of the variety of activity zoning.
4. Light Shelf Performance
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It has been shown that the exterior sky vault is the main source of glare. The preceding analysis illustrated the addition of light shelves reduced glare and affected daylighting performance by varying degrees. The light shelf: top tilted inward configuration is the best solution because it reduced glare and showed the best daylighting performance of all configurations employing a light shelf. The consideration of a larger scale more in depth HDR imagery study of this configuration would further assess its visual comfort performance during clear sky conditions. Automated shade screens below the light shelf would reduce the impact of glare caused by direct and reflected solar penetration. 5. Controls
2. Glazing Impacts Our data has shown a large magnitude of change of daylighting performance based on glass type. Unadjusted daylighting data was taken from scale models representing an ideal internal luminance environment in the uniform sky. This data was adjusted based on 70% and 22% VLT glass and compared to the actual field data. The magnitude of change of daylighting performance is considerable from the existing 22% VLT glass to 70% VLT glass. Changing the glass type would be an substantial benefit to obtaining greater daylighting performance on the 19th floor.
The impact of the changing conditions in the parameter zones coupled with the low ceiling height will require considerable integration between interior systems and electric lighting systems. Contrast between interior and exterior sources of luminance as well as the dynamic impact of both direct solar and reflected light point to the need for: •the consideration for continuous electric lighting dimming •photo metrically controlled (preferred) shade screens on the view windows Conclusion
3. Interior Reflected Component The reduction of daylighting performance from a model representing an ideal internal luminance environment (all interior surfaces approximately 80 % reflective) to one with an approximately 30% reflective floor is considerable, as seen in figures 6.1 and 6.2. This indicates that the selection of furniture and surface finishes will have a large impact on daylighting performance and highlights the importance of selecting light colored, highly diffusive non-spectral materials.
Occupant discomfort related to thermal and visual stress can be reduced by the above recommendations. A full scale mock-up will allow us to explore each issue in greater detail, this will yield a more comprehensive prioritization of those points to achieve a greater fine-tuning for occupant thermal and visual performance for the employees of the 19th floor.
/ 19th floor preliminary analysis
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