Perspective-Dependent Color-Changing Roofing Sheets Anthony Cartwright, Joseph Karas, Steven McCarthy, Brian Paige Saint Gobain Student Design Competition, 3/24/2010 Project Summary: Direct natural sunlight is capable of warming a home many degrees and can lead to drastic increases in energy bills as a result of added heating and air conditioning costs. Homes with dark surfaces are particularly susceptible to this effect in the peak of the summer months due to their tendency to absorb more radiation, warming the interior of the house via conduction. In contrast, lightly colored homes tend to reflect the ambient sunlight, thus keeping the house cooler inside. While this is far more beneficial in the warm summer months and in warmer climates, there is little or no heat recovered during the cooler winter months, and such surfaces are rendered useless in colder climates. Of all the parts of a house, the roof nearly always receives the most exposure to direct sunlight due to its upward facing orientation and to the relative positions of the sun in the sky. In concentrated residential areas, multiple roofs will absorb and radiate energy from the sun raising the local temperature of the region several degrees in a phenomenon known as the heat-island effect. This problem is especially prominent in larger cities and can have many negative impacts on the local economy. Considering both the added costs to homeowners and the adverse consequences of the heat-island effect, is apparent that there is an immediate need for technology that is capable of solving this problem. This project proposes a design for a roofing modification that will allow homes to receive the best of both worlds. This design comprises a method of separating rays of light based on the incidence angle so that viewers from street level will witness a different colored roof than if their perspective were from above the roof. Two methods have currently been proposed for achieving this effect. The first employs the concepts of lenticular printing to orient and focus light viewed from different angles to differently colored surfaces. The second method involves a hatching process that leaves grooves in the roofing surface allowing different faces of the crevice within the groove to be colored differently. Due to the increased simplicity and improvement of defects, the latter method has been selected as the primary design for the prototype. Current work to date includes a market analysis, cost estimation, and fabrication of a functional prototype. Prior Work and Competition Analysis: The concept of a cool roof has been around for several years now. Many efforts have been made to help reduce the heat island effect and to save homeowners on their energy bills. Two primary factors affecting the temperature of roofs have been identified: solar reflectance and thermal emittance.
One method found to dramatically cool the surface of any roof is the construction of a green roof. While this could refer to any form of cool roofing technology, the term is often reserved for a roof that is either partially or entirely covered in vegetation. These roofs are able to absorb rain, provide insulation, and utilize the sun s energy rather than transmitting it all to the interior of the house. These roofs, however, require high maintenance and can on occasion add substantial weight to the top of the roof. Many companies also produce highly reflective roof coatings that block solar radiation and can reduce average surface temperatures of the roof up to degrees. However, there are still several shortcomings with purely reflective roofing coatings. These coatings are limited by where and when they can best function. While they are capable of great reflecting solar radiation that can cool houses in warmer climates, they offer no benefit in colder winter regions. Because no heat is absorbed, homeowners may actually pay more in the winter months. More recent advancements have explored the potential of thermochromic roofing materials. These materials are able to respond to changes in temperature in order to optimize the effects of the roof for different times of the year. These materials are darker in the winter months when heat absorption is desirable and brighter in the summer months when greater reflection is necessary. A study conducted by the University of Athens, Greece compared the average reduction of roof surface temperatures throughout the year for various thermochromic materials to that of purely reflective materials. They determined that the thermochromic materials were, in fact, more suitable for reducing the heat island effect and offering homeowners a more stable and temperate roof. In late 2009, a team of students at the Massachusetts Institute of Technology developed their own thermochromic roofing tile trademarked, Thermeleon. These tiles consist of a typically clear plastic layered over a dark, thermal radiation absorbing surface. In warmer temperatures, when it becomes more beneficial to reflect light, a gel layer in the center of their plastic begins to nucleate, turning the tile white and reportedly scattering upwards of 80% of incoming light. One common concern about all the methods currently employed for reducing the conductive energy loss in roofing materials is the lack of freedom and choice in aesthetic appeal. One statistic provided by states that % of all houses have darker colored roofs. In fact, many residential building codes mandate that houses not have lightly colored roofs. No product currently exists that will provide the same cool roofing solutions for people living in such communities, or for people who simply desire a darker colored roof. Proposed Designs and Prototypes: Our initial design for a prototype explored the potential of a technique known as lenticular printing. Lenticular printing utilizes sheets of plastic layered with tiny semi-cylindrical lenses that orient lines of light toward one of two images. Depending on the customization of the lenses
and background image, one may control the viewing angles at which either image can be seen. This technology could effectively be used to separate any roof into tow sections. The top view of the roof would only be visible from above, and the street view would only be seen from below the roof. The two colors under the lenses may then be constructed in such a manner as to allow the Top Roof to best reflect or absorb sunlight while the bottom roof remains whatever color the homeowner wishes to appear when viewed from street level. Further research has lead to modifications seeking to both simplify and improve the designs initially proposed for the product by removing the need for lenses and specialized lenticular processing. Current plans for the prototype comprise a sheet of We would also like to highlight a few of the assumptions made to simplify the process, and to identify the basis on which each assumption was founded. First, it may be assumed that the bulk of the direct sunlight affecting the roof will be seen between the hours of 9am and 5pm while the sun is highest in the sky. At lower angles, the sun does not provide direct sunlight and is often blocked by taller structures and local foliage. Next, it was assumed that any lenses or grooves would be oriented in such a manner that, when placing an imaginary plane parallel to the Earth s surface at the height of the roof, only the Street View would be visible beneath said plane and only the Top View would be visible above the plane. Market Analysis: The possible access points for introducing this product to the market are vast, and each has its own unique perquisites and advantages. The most direct market for the modified roofing would be to sell the product straight to the end consumers, the individual homeowners. Custom roofing could be designed and installed upon request. Due to the simple nature of the design, it is also not unfeasible that the product could be distributed in do-it-yourself kits allowing people a relatively cheap energy-saving option they can apply without the added cost of professional installation. The do-it-yourself trend has been growing in popularity in recent years and could offer some market recognition. It is also well known that certain consumers will pay a premium for items with options for customization or personalization. One example would be a custom painted car. The appeal of freedom in design can attract an entire new market of customers. Due to the potential for our product to be custom designed for various viewing angles, this would prove to be an excellent niche market for our product to target. This would also allow for higher margins as custom products always carry a premium. While energy savings around the house are a certain benefit of implementing this technology, the freedom to choose whatever images appear on the top side or street side of the roof opens the door to an entire realm of new possibilities. This could pave the way for new concepts of designer roofing. People could add artistic twists, luxury designs, or even advertisements to the roof of their home or business. Yet another major market to consider could be to target this product toward contractors, developers, warehouses, and stores that can ultimately. If readily accepted by contractors or
building regulators, much time and effort could be saved from obtaining permits and approval for use of the product on actual houses. Additionally, if they could turn around and turn a profit using the attractive properties offered by our design, it is not unthinkable that they would pay for our product. Furthermore, many of these people or organization have experience and history with advertising or selling roofs and could do so without investing excess time. Geographically speaking, the flexibility of our design to accommodate any coloring or coating on the two separate surfaces allows us to target locations at nearly any latitude. For more southern regions, the top view of the roof could consist simply of a reflective coating, whereas in more temperamental climates, the top surface could take advantage of many of the new advancements in thermochromic materials. Costs and Profitability Analysis: Cost is a large concern for roofing due to the investment involved. There are various types of roofing, and their associated installation costs are listed in the table below. It should be noted that removal of a current roof can be $3 5 per square foot, costing as much as $510 1,100 for an average 1,700 2,100 square foot roof. Costs for removal may be higher depending on the type of material to be removed. Material Type Cost per Square Foot Cost for Full Installation* Asphalt Shingle $1 4 $1,700 8,400 Wood Shingle $4 7 $6,800 14,700 Wood Shake $6 9 $10,200 20,000 Fake Wood Shingle $6 9 $12,600 18,900 Concrete Tile $4.50 10 $7,650 21,000 Ceramic Clay Tile $7 30 $11,900 63,000 Steel Shingle $3 10 $5,100 22,000 Aluminum Shingle $7 15 $11,900 24,200 Copper Roof $15 18 $25,500 39,600 Slate Roof $9 40 $17,000 84,000 Synthetic Slate Roof $7 9 $11,900 18,900 *costs include installation on an average ranch style house with a 1,700 2,100 square foot roof. i Another important factor is the amount of time that a roof will last. Included below is a table of various choices of roofing materials and their average life spans. It should also be noted that the cheapest and most common roofing material, asphalt, does not last nearly as long in warmer climates that receive larger amounts of sunlight. Material Expected Life Span (in Years) Asphalt 12 30 Wood Shingles/Shakes 25 50
Slate 50 + Metal 50 + Ceramic Clay Tile 60 80 iiiii In order to determine an ideal cost for our product that will provide it with a profitable, competitive edge, the most important factor to consider is the cost of raw materials, with the secondary costs being processing and installation. For any reception in the market to occur, the maximum pricing point for the full roofing installation should fall within the constraints of the higher end prices for materials like clay and slate. Perhaps a more ideal price point, however, would lie comparable to some of the less expensive choices for roofing materials, such as asphalt roofing tiles. Regardless, these tiles offer the added benefit of reducing heating and cooling costs, offering prospective consumers an immediate incentive to purchase our product over other alternatives. The profit savings on the end of the consumer will facilitate our primary selling point, and will also function as our own greatest potential for profit. The other main factor for eliciting market adoption is the ability to sell customers designer roofs. By using this technology not just for purposes of energy savings, but also to appeal to people looking for a luxury roof or an artistic roof, we can exploit an entire new market as well. Given the numerous approaches available for introducing our product to the market, the feasibility and practicality of the product are very clear. i http://www.costhelper.com/cost/home-garden/roof.html ii http://www.thisoldhouse.com/toh/article/0,,198504,00.html iii http://www.galttech.com/research/household-diy-tools/new-roof-replacement.php