As the cost of energy rises, nearly everyone is looking at ways to improve their homes energy efficiency, and reduce their energy use and costs. Our project focused on finding a method to utilize the roof of a home to be an integral part of the energy system of a home.
The concept of this idea began in a discussion concerning sustainable design, in last year’s senior class. One student presented the question, “Why don’t we have color changing roofs that would take advantage of the sun’s energy in the winter, and reflect it in the summer?” Good question! It was with this question in mind that our InvenTeam was established.
Washington County Technical High School was chosen along with 15 other schools around the country by the “MIT-Lemelson Foundation” to receive a $6,000 research grant. We recruited students from multiple vocational areas, whom could lend their individual capabilities on a wide variety of subjects dealing with the design of this project. The members of this team included students from areas such as child care, computer repair and networking, digital communications, multimedia and graphic design and more.
We believe this to be a necessary and viable invention, because we found other individuals seeking solutions to similar problems, and a recent statement by Energy Secretary, Steven Chu in which he said, “Giving roads and roofs a paler color would have the same effect of removing every car in the world off the roads for 11 years.”
One of our biggest challenges was the lack of published data concerning heat collection in the attic space of homes. We contacted a group of MIT graduate students (who are developing a similar invention) and Secretary of Energy Steven Cho. Neither could share any usable data.
Thanks to the generosity of David Vernier of the Vernier Software and Technnolgy Company, we were able to collect some significant data that leads us to believe we have a viable idea. Mr. Vernier loaned us a LabQuest unit and several temperature probes that allowed us to gather the data we needed. The team built two scale model homes to collect the data. The test homes were constructed and insulated exactly like any 2 x 4 wood framed home. One model had a black shingled roof and one had a white shingled roof.
Here you will see graphs of the initial data we collected with the LabQuest from the two test homes.
As the data shows the temperature in the black shingled roof is 7-10 degrees warmer than the white shingled roof. Also note that even in a relatively cool period (around 60 degrees) the temperature in the attic space can be as high as 20 degrees warmer.
We believe a thermostatically controlled, photo-voltaic powered ventilation system could be used to move this warm air into the living space and decrease the home owners heating costs.
What surprised us was how little of the heat build-up in the attic was radiating into the living space, which you can see remains relatively constant. Upon further analysis, we felt the heat build up in the attic, though not directly impacting the interior temperature, would have an affect on attic based central conditioning systems.
Our solution to the problem was to take PVC tubing and paint the half black. A gear would be attached to the base of each tube and a motor would rotate the tubes 180 degrees, changing the roof from blck to white. The next series of graphs shows the affect the tube based color changing roof had on the attic space. We placed our tube unit on the white roof first, white side up, to compare our solution with a black asphalt roof.
See how dramatically the tube unit reduced the temperature in the white attic space. The white tube attic was just a few degrees above the outside temperature. This proved that our white tubes could really reduce heat build-up in the attic. Next we need to to see if the black tubes would collect heat as well as an asphalt roof.
Here you can see that our black tubes did not perform as well collecting heat as a normal black asphalt roof. Clearly the air space between the black surface of the tubes and the surface of the roof was reducing the heat gain.
Our next experiment involved using an aluminum tube instead of the PVC tubes we used originally.
This graph shows that an aluminum tube would collect heat about as well as the black asphalt shingle.
In conclusion we believe the best design for a tube based color changing roof would to have a tube that is half plastic (non-conducting) and half aluminum (conducting). The white plastic side would be up whenever the outside temperature reached around 80 degrees. If the temperature drops below 65 degrees the tubes would rotate the black aluminum side upward and air would be blown up the tubes and into the homes living space, as needed to keep the space around 70 degrees.