Project/Composite Daylighting

From Drexel Smart House

Jump to: navigation, search

The purpose of this research is to design and build a fiber-optic daylighting solution for the residential built-environment. Additionally, the fiber-optic system will be supplemented with LEDs to provide consistent light output from the system. The system will detect changes in light throughout the day and adjust the LED brightness accordingly.

Contents

Background research

The luminaire will be modeled and simulated in Desktop Radiance, a GUI for Radiance.

Initial luminaire modeling will be performed in Ecotect until Radiance is installed on CAD lab machines (needs administrator authorization and access to AutoCAD)

Prior work

Concept Design

The design consists of several components. A concave mirror will be mounted on a solar tracking mount, adapted from a photovoltaic mount. The solar tracker will automatically adjust the mirror so that the focal point always rests on the fiber bundle throughout the entire day. Additionally, a cold mirror will be placed several inches ahead of the focal point, reflecting the visible focal point back into the concave mirror. IR radiation selectively passed through the cold mirror will be absorbed by a photovoltaic cell to provide some power to the system.

The visible light reflected from the cold mirror will be carried by fiber optics to the luminaires. At the luminaires, LEDs will be used to supplement the daylight to provide a consistent color temperature throughout the day. The amount of compensation required will be determined through a light sensor built into the fixture. Lastly, a shutter will be used to dim fibers within the luminaire, while a pulse width modulation driver will be used to dim the LEDs.

Fiber Optics

Both quartz and polymethylmethacrylate (PMMA) fibers are under consideration. Depending on further research, it may be necessary to coat the raw fibers to increase transmission. The coating must be a high refractive index coating in order to promote internal reflection.

Solar Collector

A polycarbonate concave mirror will be used to focus up to 1.5 square meters to a central point of approximately 1.5 inches in diameter. A collector dish will be mounted to a solar tracker using a steel or aluminum mounting ring which will clamp on the edges of the dish and apply tension to a second ring which will center the middle of the dish. All mounting hardware will be fabricated in house.

A supplier for the concave mirror has not yet been identified. Due to budgetary constraints, the focal length of the mirror will be decided once an inexpensive source is found.

The optical assembly mounted near the focal point will consist of a cold mirror and photovoltaic assembly. Mounting and assembly hardware must be heat resistant. The cold mirror will be purchased from (or donated by) Edmund Optics. The purpose of the cold mirror is to reflect visible light onto the fiber bundle, reversing the focal point back into the interior of the concave mirror. The cold mirror is designed to pass IR radiation, which will be absorbed by a photovoltaic cell directly behind the cold mirror.

Alternatively, a UV and IR filter stack designed to pass visible light can be insulation mounted into an evacuated glass enclosure, then water-cooled to generate electricity by solar water heating. Due to budgetary constraints and the challenges involved with a solar water heating system, the cold mirror and photovoltaic assembly will be developed.

Solar Tracker

Communication has been opened between Drexel Smart House and Wattsun Inc. out of Albuquerque NM. Wattsun has manufactured a solar tracker in the past for ORNL daylighting research. It is our hope that they will be willing to either donate a tracker to us or manufacture one for us at cost.

Passive solar trackers are still under consideration; a decision will be arrived at after further research.

Fixture

The fixture is considered a separate entity from the solar collector, although the two are connected by the fiber bundle. The fixture will incorporate LEDs, a color temperature sensor, fiber optics and a shutter, a light diffuser, and control electronics. The fixtures will behave like a conventional light fixture and will be capable of outputting consistent light 24/7.

Luminaire Design

The luminaire will be a pendant fixture housing several main components. The heat sink assembly is the part to which LEDs and fiber optics are mounted. Facing the heat sink assembly is some type of diffuser (either a reflective diffuser or a diffusion filter), and facing the diffuser will be the sensor assembly. The power supply, embedded controller, and pulse width modulation circuits will all also be housed within the luminaire. Other components of the luminaire include, but are not limited to: Fixture shell, some kind of lens (acrylic?), anodized Al alloy reflector (or some kind of reflector), dust cover, some kind of ballast, canopy, and mounting chassis.

Sensor

Agilent Colorimetric CMOS Sensor

An inexpensive sensor must be designed to detect the total light output's colorimetrics. In order to accomplish this, three inexpensive photodiodes or monochromatic detectors can be coupled with red, green, and blue band pass interference filters. The voltages outputted by the detectors, when measured precisely and calibrated through software to standards, will indicate the light's color temperature.

Agilent Technologies manufactures a full spectrum CMOS sensor that will be perfect for our luminaires. It's dimensions are 5x5x1 mm, and it outputs three unique voltages placing the light's color on the RGB spectrum. We can purchase them in small quantities for $10 / each or get several samples, or they can be purchased in bulk (1000+) for $5/ea.

Artificial Light Supplementation (LEDs)

High powered LED chips will be mounted to a heat sink with through holes for fiber optics blended in. Since all of the LEDs and the fiber optics will be point sources of light, it will be necessary to diffuse the combination of all of the light.

Future Lighting Solutions will be donating LED materials for this research project. The design will incorporate high powered, 5 watt LED chips arranged on the heat sink (Lumileds, manufactured by Philips). The 5 watt LEDs dissipate approximately 2.5 watts of heat each, so thermal dissipation and proper design must be taken into consideration.

In order to supplement color matched light (and to compensate in spectral changes due to fiber optics and other optics), the luminaire will use several red, green, and blue LEDs in addition to the white LEDs. The color LEDs will be dimmed individually using pulse width modulation to produce necessary colors. The white LEDs will also be dimmed and powered using pulse width modulation so smooth transitions can be made during periods of cloud cover and darkness.

Quantities of LEDs necessary to light the luminaire will be determined experimentally.

Power Supply

The power supply will manage power for the fixture and will run off of a low voltage line. The power supply will provide low voltage power to the embedded controller, the dimming pulse width modulation circuit, the sensor circuit, and the shutter.

Control

The control system will be designed by the electrical and computer engineering students. The system should be capable of dimming the lights to user-designated levels. Additionally, it should be designed in such a way as to integrate into a larger control system and a broader lighting environment.

Embedded platform

To be researched and selected by the senior design team.

Embedded Software

Pulse Width Modulation

Shutter

The shutter will be oriented directly in front of the fiber optics in order to control the daylight output. Control over this output will allow for conventional dimming of the entire hybrid luminaire.

Since LED spacing is critical to manage heat within the aluminum heat sink, the fibers will likely require dispersing. The shutter can be implemented as a strip that covers varying amounts of fiber ends, depending on its position.

Testing Methods

Testing for the overall system can be done quickly and easily using a spectrophotometer, such as a Photo Research Spectrascan PR-655. However due to budgetary constraints, individual optical tests will need to be devised for the various required tests unless we can find access to a spectrophotometer. Additional tests are detailed below.

Tensile Deformation Strain Testing of Fiber Optics

If PMMA fibers are selected, Instron tension tests will be performed to strains of 2, 5, and 10% to create deformation. Attenuation tests will then be performed on the deformed fibers to test for transmission loss. There will be two trials of these tests.

Bend Radius Attenuation Tests of Fiber Optics

Regardless of fiber choice, the bend radius of the fiber installation will determine the ultimate attenuation of the fiber bundle (i.e., the number of turns and curves overall along the fiber from the solar collector to the luminaire). Obtaining a bend radius attenuation curve will be done using a monochromatic source and detector setup with a straight length of fiber as a control. The fiber will be looped to a measured radius, and transmission will be measured across several data points as the radius of the loop is decreased. Data obtained will be compared to manufacturers attenuation ratings.

Bend Radius Deformation Tests of Fiber Optics

In order to determine the smallest bend radius the fibers can be subjected to, destructive tests measuring the minimum bend radius will be performed. For PMMA fibers plastic deformation will take place past a particular bend radius while breakage will occur for quartz and glass fibers. This testing is necessary because the optical properties of PMMA are modified after plastic deformation.

Additional Materials Concerns & Possible Tests

Other areas that will be investigated include jacketing of the fibers, cold mirror selection, and monochronometer analysis of the fibers. Also, we will be investigating the possibility of coating the fibers with a coating with higher index of refraction. This will prevent light leakage from the fibers.

Timeline

Budget

Personnel

Principal Investigators
Interior Design: Dr. Eugenia Ellis
Materials Engineering: Dr. Caroline Schauer
Architectural Engineering: Dr. Jin Wen

Design Course Team
Project Leader: Eric Eisele
Civil Engineer: David Delisi
Design Expertise: Akshita Sivakumar

Senior Design Team
Materials Engineering: Jameson Detweiler
Electrical & Computer Engineering: Thaddeus Konicki
Electrical & Computer Engineering: James McCann
Electrical & Computer Engineering: Luke McCrone

Contacts

Retrieved from "http://www.drexelsmarthouse.com/wiki/Project/Composite_Daylighting"