In the weeks following Hurricane Katrina’s landfall, New Orleans was without electricity and potable water. Due to this, there is a need to use natural sources (sun, water, and wind) as a secondary means to make the shelter an independent structure for a short period of time. This will be achieved by collecting and storing the sun’s energy through utilizing solar fabric, similar to those found in solar, as well as a cistern system.
The first element to create an independent shelter is photovoltaic fabric. Photovoltaic (PV) fabric, which is made by layering a semi-conductive material around fibers, can be used to harvest the sun’s energy, as well as shading a structure from internal heat gain. In the market of solar fabrics, there is one product that has made some cutting edge breakthroughs. Researcher at Herriot-Watt University in Edinburg, UK, Tapas Mallick is experimenting with the highly refractive material, peispex, to complete a process called total internal reflection. In this process, because of the concentrators shape, sunlight cannot escape; therefore, the light bounces around until it reaches a PV cell. By incorporating this, Malick’s calculations show that one square foot of his fabric can produce up to 200 watts of usable energy. In addition, “when [applied] to a window, the [solar fabric] would allow 25% of the available light through to illuminate the room. In addition, the remaining 75% is used to generate electricity” (Knight , 2010, para.7). The photovoltaic fabric would block the sun’s direct rays, as well as using its power to provide electricity to the temporary shelter.
Image 1 - A shelter using solar fabric to lighten the useable spaces during the night or a cloudy day
The first element to create an independent shelter is photovoltaic fabric. Photovoltaic (PV) fabric, which is made by layering a semi-conductive material around fibers, can be used to harvest the sun’s energy, as well as shading a structure from internal heat gain. In the market of solar fabrics, there is one product that has made some cutting edge breakthroughs. Researcher at Herriot-Watt University in Edinburg, UK, Tapas Mallick is experimenting with the highly refractive material, peispex, to complete a process called total internal reflection. In this process, because of the concentrators shape, sunlight cannot escape; therefore, the light bounces around until it reaches a PV cell. By incorporating this, Malick’s calculations show that one square foot of his fabric can produce up to 200 watts of usable energy. In addition, “when [applied] to a window, the [solar fabric] would allow 25% of the available light through to illuminate the room. In addition, the remaining 75% is used to generate electricity” (Knight , 2010, para.7). The photovoltaic fabric would block the sun’s direct rays, as well as using its power to provide electricity to the temporary shelter.
Image 2 - The process of storing solar energy in a battery
The second element to create an independent shelter is storing the solar energy. Following a natural disaster, an area’s electricity can be down for several weeks, if not months. Therefore, there is a need for a secondary power source. This secondary source is solar energy. However, there is a need to store unneeded energy for use on cloudy days. The solution to this is the use of solar energy battery cells. Deep cycle batteries are used in the storage of solar energy, due to the fact that they can discharge as much as 80% of their energy, over a longer period of time, without significant damage to the battery. The type of deep cycle battery that will be incorporated into the shelter will be an AGM (Absorbed Glass Mat), due to the fact that its advantages and its ability to withstand harsh environments overweigh its increase in cost. The following is a bulleted list of the AGM battery’s advantages:
· No maintenance is required
· It can withstand shock and vibrations
· Its ability to take abuse
· It is completely sealed against releasing fumes
When choosing a battery, it is important to research the lifespan of that battery. To determine a battery’s lifespan, you must take into account its cycles and the temperature effects on that battery. The first characteristic, a battery’s cycles, is the main determinate of the battery’s lifespan. A cycle occurs every time the battery’s stored energy is discharged. For example, “a battery [that] discharges 50% everyday will last twice as long as one that is cycled to 80%.” The second characteristic, the temperature’s effect on a battery, can increase or decrease a battery’s life and storage capacity. The standard temperature for rating a battery is 77 degree Fahrenheit. At 32 degrees Fahrenheit, the storage capacity is reduced by 20%; however, the lifespan increases by 60%. At 122 degrees Fahrenheit, the storage capacity is increased by 12%. In addition, for every 15 degrees over the 77 degrees standard, the battery’s lifespan can be reduced by 50%. In average conditions, an AGM deep cycle battery can last up to four years (Deep Cycle Batteries, n.d.).
Imgae 3 - A water collection cistern system
The third element in creating an independent shelter is water collection and minimalization. The first step, when sizing a cistern system, is determining the total water consumption of the shelter per day. In a post-disaster situation, the top priority must be water conservation. Due to phys.ufl.edu, the average water usage per day per person is 30 gallons. In addition, the production rate per square foot of roof area per inch of rain is 0.6. However, the 30 gallons refers to an average household, which includes during laundry and three sinks. By removing the laundry component and reducing the sinks to two, the water needed per person per day is condensed to 21 gallons.
Using these variables, a shelter, which houses 3 people for 60 days, would require 3,780 gallons of water (21 gallons per person per day x 60 day shelter duration x 2 people). In addition, a 400 square foot shelter, with a 2 foot overhang, can produce 345.6 gallons of usable water per 1 inch or rain (567 square feet of roof area x 0.6 production rate x 0.1 overflow coefficient) (Determining Need, n.d.). According to The Weather Channel, the average precipitation per month in New Orleans, during peak hurricane season (June - August), is 6.4 inches. Therefore, the 3,780 gallon minimum can be surpassed (345.6 gallons x 12.8 inches = 4,423.7 gallons) (Monthly Averages, n.d.).
Image 4 - The process of turning human waste into usable fertilizer using a composting toilet
The best solution to minimize water use is to install a composite toilet. In 1971, Hardy Sundberg developed the first waterless toilet reducing the average domicile water average by 45%. This is accomplished by using “aerobic bacteria to convert the carbon atoms in the waste to carbon dioxide, and the hydrogen atoms to water” (The History of, n.d., para. 1). Therefore, the separated water can be used and collected in a grey water system. In addition, utilizing the aerobic bacteria and the three step process of composting, evaporation, and finishing, a composite toilet can have many advantages which include being an odorless system, using little or no water, and can be installed anywhere (The History of, n.d.).
Image 5 - How the Bernoulli porduces a lifting force
The fourth element to create an independent shelter is counteracting the wind’s lifting force. Utilizing an area’s wind pattern can decrease a structure’s dependency on electricity. However, a major problem with structures located in tornado and hurricane-prone areas, is the wind’s ability to create a lifting force which can demolish a structure’s roof. The most popular way for a structure to become destroyed in a high wind situation, is the lifting the roof. Once the roof is removed, the integrity of the overall structure is weakened, usually resulting in the total destruction of the structure. Using Bernoulli’s Principal, a roof can be designed to withstand the pressure a hurricane’s wind can produce. Bernoulli’s Principal accounts for the pressure difference, on the interior and exterior of a structure, during a hurricane or tornado.
Image 6 - How the Bernoulli Effect's lifting force affects on a house
In a hurricane, the air in a structure is still; therefore, in Bernoulli’s equation, “the pressure difference between the inside and outside of the roof is half the air density multiplied by the wind speed squared (Heckert, P). During a 150 m.p.h. category 5 hurricane, with an air density of 1.3 kilograms per cubic meter, the difference in pressure from inside to outside is 0.4 pounds per square inch. For the 250 square foot Uber Shelter, there would be a lifting force of nearly 14,400 pounds (multiplying 250 square feet by 144 square inches per square foot by 0.4 pounds per square inch). However, a roof’s mass must be calculated to determine the net lifting force.
Assuming [a roof] has about the same density as water (1,000 kilograms per cubic meter), a roof’s mass can be roughly estimated. Wood is less dense [than water], thus it floats; however, nails and roofing materials are denser, [as a result, the two approximately average out]. Mass is density times volume. If [a 250] square foot (22.5 square meters) roof is about 0.1 meters thick, its volume is 2.25 cubic meters. Multiplying gives an approximate mass of 2,250 kilograms, [which rounds to] 4,500 pounds (Heckert, 2007, para. 7).
The net lifting force of 150 mph winds on a 250 square foot roof (the lifting force minus the weight) equals about 9,900 pounds.
To contradict the lifting force of the Bernoulli Effect, certain measures need to be taken to firmly anchor the roof to the walls and ground structure. The forces are then transferred to a solid foundation. In traditional domicile construction, roof trusses are toe-nailed to the top of walls, providing little to no structural strength. However, many products have been designed to improve traditional anchoring systems. One technique is to nail metal straps to the wall, which then wrap over the truss. Another technique, temporary hurricane straps, can quickly anchor a roof structure to the foundation, ensuring structural strength (Heckert , 2007).
Deep Cycle Batteries. (n.d.). Northern Arizona Wind and Sun. Retrieved January 4, 2011, from
http://www.windsun.com/Batteries/Battry_FAQ.htm
Determining the Need. (n.d.). Retrieved January 2, 2011, from htpp://www.phys.ufl.edu/-liz/
water.html
The History of SUN-MAR is the History of Composting Toilets. (n.d.). Retrieved January
2, 2011, from http://www.sun-mar.com
Heckert, P. (2007, May 15). Why a Tornado or Hurricane Can Lift the Roof off a House.
Retrieved January 3, 2011, from fttp://wwwsuite101.com/content/bernoullis-principle-
and-storms-a21290.
Knight, H. (2010, April). Green Machine: Cheaper Home Power from Sunlight. Retrieved
January 2, 2011, from http://www.newscientist.com/article/dn18822-green-machine-
cheaper-home-power-from-sunlight.html
Monthly Averages for New Orleans, LA. (n.d.). Retrieved January 4, 2011, from http://www.
weather.com/outlook/travel/vacationplanner/vacationclimatology/monthly/USLA0338
Images
Image 1 - http://www.treehugger.com/orange-solar-tents-image.jpg
Image 2 - http://sunenergyfacts.com/wp-content/uploads/2008/02/solar-energy-storage.jpg
Image 3 - http://www.thecistern.comstorage/roofcooling__diagram.jpg
Image 4 - http://static.howstuffworks.com/gif/composting-toilet-diagram.gif
Image 5 - http://reniyoung.files.wordpress.com/2010/11/bernoullis-principal.jpg
Image 6 - http://www.stormsurvival.org/image/windforces.JPG
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