Allison Brown



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Daylight Conclusions (diffuse vs. clear):

(Note: The Lightscape software can’t analyze diffuse glazing accurately. All calcs were taken from Luxczon *see appendix*)

*Clear glazing, June 21st. 10:00 am, clear sky conditions vs diffuse

Daylight Conclusions (tinted vs. diffuse)

Tinted Glazing June 21st, 3:00PM, clear sky conditions

*Polycarbonate glazing, June 21st, 3:00 PM

Energy Analysis: Peak Heating and Cooling

Energy Conclusions

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Founder’s Gallery

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Design Ambitions

Glazing Considerations

Glazing Material Options:

- Clear

- Tinted

- Diffuse (acrylic and polycarbonate)

Daylight Availability Study:

- Introduction to criteria

- Luxicon well calcs for various glazing types and time of year

Availability Conclusions

HAP Analysis for Curtain Wall and Skylight

- clear glazing (low e coating)

- tinted glazing

- tinted glazing (low e coating)

- tinted reflective glazing (low e coating)

Final Conclusion and Recommendations

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Ceiling Height = 16’-0”

Introduction

Circulation Desk

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Skylight Well

Circulation Desk

Curtain Wall (A= 1474 ft^2)

Design Ambitions:

In the skylight lobby exists a circulation desk directly beneath the southern skylight well. Direct sunlight should be avoided on the secretary’s work surface to avoid harsh hot spots and glare. The existing glazing system is insulated tempered tinted glazing which could still potentially serve as a drastic glare source and produce distinct patterns of high luminance. The wells are also extremely deep which will also enhance clarity of the hot spots on the floor and walls. I have previously explained that harsh patterns of luminance variances could be potentially distracting to the partially sighted. On the southern end of the gallery exits a 19’ high glass curtain wall which I also will evaluate the solar gains through an energy comparison. I also predict that because the wall is south-facing, the desk may also be in direct sunlight from the curtain wall as well during the winter months. My overall goal is to investigate the performance of different types of glazing on the basis of visible light, energy analysis, and aesthic quality.

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Well Height = 16’-0”

Skylight

Skylight

Skylight well: Á - .90

Room Wall Á = .35

Floor Á = .20

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Structural Partition

Windoρ - .90

Room Wall ρ = .35

Floor ρ = .20

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Structural Partition

Windows have two component of heat transfer: conduction and transmission solar radiation. For glazing two components are important to analyze: the U value of the glazing and the SHGC of the glazing. Given the large south facing glazing in the space, I felt it would be valuable to calculate the difference is the heat transfer of different glazing materials.

➢ Solar gain is the sum of the transmitted radiation through a glazing and the portion that is absorbed

➢ Conduction heat gain per unit area is the product of the U (coefficient of heat transfer) of the glazing and the outdoor-indoor temperature difference.

➢ Total heat gain = Solar heat gain + conduction heat gain

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Daylighting Conclusions:

By observing the data, I concluded that due to the deep wells, the sun is rarely in the line of sight of secretary’s desk; however the image preserving glazing does produce harsh hot spots throughout the space especially during the summer months. Due to the large area of glazing of the skylight, I feel a diffuse system will be most appropriate for the space when considering defined circulation patterns for the visually impaired as illustrated below. From a lighting standpoint, during night hours, diffuse white glazing would be able to be used glazing as a surface to illuminate and “mimic” daytime conditions during the night hours. The architect also requested he wanted the skylight to be seen from the exterior and to “glow” at night which would not be possible with image preserved glazing.

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The tinted image preserving, glass also produces distinct hot spots on the walls and floor and produces color rendition problems in the space by casting a green glow.

If polycarbonate glazing is used, the maximum illuminance on the surface of the desk is 490 fc with an avg of 463 fc yielding a STD of 14. The polycarbonate glazing yields a much more uniform illumination for the secretary’s task. Even though the light level is high it is interested to note that daylight is perceived differently and a higher light level is tolerated. This lower level of light and even illuminance as compared to the clear and tinted glazing will also serve as an easier transition into the interior spaces

*Partially sighted view of clear glazing vs diffuse glazing (color distortion, increased brightness, decreased visual clarity, decreased contrast sensitivity)

Glazing Considerations

The choice of the glazing material can have an enormous effect on the quality of light provided and the energy efficiency of the design. Factors include:

➢ Tvis (visible light transmittance)

➢ Diffusion (transparency of the material)

➢ SHGC (solar heat gain coefficient) measures the amount of the solar spectrum that will pass through a material: including ultraviolet, visible light, and infrared radiation. All of this energy heats a building.

➢ U-value of the skylight unit assembly measures the heat transfer capabilities when placed between two spaces of different temperatures. Usually increasing the numbers of glazing produces higher insulated qualities, but will also lower the SHGC and Tvis of the skylight.

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(Terms and definitions)

Glazing Efficacy is the measure of how much light penetrates all the layers of glazing in relation to how much solar heat gets through. (LSG) Specifically it is a ratio of the visible transmittance (Tvis) to the solar heat gain coefficient (SHGC) of the glazing.

Solar to Heat Gain Ratio (LSG) is the ratio of Tvis to SHGC. Thus the higher the LSG, the more efficient the glazing.

Low-emissivity coatings are applied to a surface of glass or polyester film, however they are not applied to plastic materials which are heated to form. The purpose of these coatings is to reflect specific portions of the solar spectrum.

Reflective Glazings reflect the visible spectrum which lowers the SHGC

Direct Solar Control:

Diffuse Glazing: There is no standard to describe diffusion properties, however a quick test can be made by looking through the translucent material. If any image can be seen, some portion of the light must be passing directly though (image preserving), and thus the material will not be highly diffusing. Most acrylic and polycarbonate glazings in their “white” products are considered diffusing. Generally, transmittance and luminance decrease as diffusion increases.

Shading Devices: Interior shading devices include horizontal louvers, roller shades, screens, and shutters. These devices are intended to block the direct sun at certain sun angles. They are however of a high initial cost and create many maintenance issues (accumulation of dust or costly replacement) and thus I determined they would not be an economical choice for use on the skylight for this space.

Test Glazings

For the skylight daylight availability analysis, I decided to test the acrylic, polycarbonate, clear glass, and tinted glass. For the energy analysis, I also incorporated the curtain wall, testing the three tinted glazing types. Cooling loads typically dominate in large commercial buildings, so I predict a low SHGC will be desirable to keep the cooling loads to a minimum. Ideally, the best performance glazing will have the highest LSG, but it may not be appropriate when considering the visual tasks beneath the skylight.

Daylight Availability Analysis:

I decided to test the four different types of glazing for the extreme case on the basis of energy and sun position: June 21st and December 21st for both clear and overcast sky conditions. I used Luxicon software to perform my analysis. Given the restraints of the software, the geometry of the skylights and of the room had to be simplified. I performed the trials during three different times of the day: 10 AM, 12 PM and 3 PM which would be crucial working hours for the secretary. The light levels calculated might be on the lower side as well since the pyramidal shape of the skylights will create more surface area of glass and thus more of the sky light will contribute to the space.

As you can see on the right, on a clear day in the morning, the clear glazing produces large distinct hot spots on the walls and floor. Since the desk and floor surfaces are somewhat glossy, this could be a huge problem for reflected and direct glare. From the data calculated in Luxicon, the maximum illuminance on the surface of the desk is over 7000 fc, towards the left hand side of the desk to an avg of 1700 fc yielding a standard deviation of 1667! This would be a very uncomfortable environment for someone to work under unless some shading devices were used. However, due to the under overcast conditions, the clear glazing will perform as a diffuse system:(443 fc avg.)

HAP Analysis: Sensible and latent heat determines the total heat gain within a space. Using Carrier’s HAP Analysis, I compared the differences in sensible heating only. I used the default opaque materials for exterior walls and added the curtain wall glazing and skylight glazing in the space to attempt to determine the difference in total heat gain and the maximum cooling and heating loads for the space. The latent loads were assumed to be zero, since I am only interested in comparing the glazing types.

The tinted reflective low e glazing in combination with the polycarbonate panels performed the best when considering both the heating and cooling loads to the space. Reflective glazing, however, can be a source of glare for surrounding buildings, and due to the building’s location, it would not be recommended. The tinted glazing also has a better performance, however since the space serves a “image maker” of the building, color rendering is definitely important. However, by choosing the clear low e glazing for the atrium glazing in combination with the polycarbonate skylight system, I actually improved the load by .1 tons will not be a drastic enough of a change to resize the chillers in the building.

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Final Recommendations

➢ Curtain Wall = 1” Insulated clear (low e-coating)

➢ Skylight = 12mm polycarbonate panels

During the winter time, given the southern orientation of the curtain wall, the sun will penetrate deeper into the space. When investigating the winter months, I discovered the glare source was provided by both the curtain wall and the skylight. It would be highly recommended that either an overhang be implemented or shading devices especially during the morning and late afternoon hours during the winter months.

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