Renewable Energy

Earthships

When my students enter high school they will begin to study contemporary issues. Energy availability is and will continue to be of high importance. But other issues will come to the forefront as they mature. There appears to be a widely held assumption that water, not oil, will soon become the most valued resource on earth. Underdeveloped and immerging nations such as China will require more energy and in the process produce more trash. How will the world handle these issues? With the background knowledge gained through this unit of study, my students will be prepared to make realistic decisions regarding the future of the world. Earthships were mentioned earlier in this unit. They came to mind as I considered the problems facing modern China and the impact that China's growth will have on the rest of the world. We will culminate our study of architectural alternatives by investigating this innovative structure called the Earthship. Almost every aspect of modern living is adapted to renewable energy in this sustainable system.

Michael E. Reynolds of Taos, New Mexico has created a design for home building which is affordable and innovative. He accomplishes this by using recycled trash and earth as building materials. Reynolds sees garbage as a renewable resource. By using such items as used tires and beverage cans for construction he is able to use one problem to solve another. "Garbage is a renewable resource-and we don't have to worry about raping the Earth to get it [31]." These Earthships can operate off of the grid and are designed to be totally self-sustaining. An Earthship provides its own heating and cooling, water, and sewage treatment. Electrical power is generated through photovoltaic cells and wind turbines. Food can be grown year round in the interior, no matter what the climate.

How does he do this? A brief description was given in the introduction; now I will give more detail. I strongly recommend pulling up pictures or videos from the bibliography when studying these homes in your classes. To take advantage of the free solar energy, Reynolds chose to create walls in his homes with a capacity for high thermal mass. This is where tires come into the picture. Thermal mass is any substance which can contain temperature. Earth, adobe and other bricks, rock, concrete and water are all thermal mass materials. Concrete is not renewable and comes with a price tag. That price can be calculated in dollars and CO ₂ emissions. "Roughly 7% of greenhouse gas emissions worldwide stem from the manufacture of Portland cement — a major component of most concrete mixtures [32]." With bricks, there is also the issue of transport, cost, and the environmental consequence of brick making. The energy equivalent of one gallon of gasoline is needed to manufacture eight common building bricks [33].

Water is the best material for thermal mass. It is used in radiant floor heating in contemporary construction. Hot water runs through tubes embedded in a slab. The heat radiates upwards towards the cooler air. It is a good system, but it does require the use of fossil fuel and mechanical technology for it to work. I have seen water used to retain the heat from solar gain. Friends had a huge cylinder of plastic (about six feet across) reaching from floor to ceiling in the entryway of their home. It absorbed the sun's energy and radiated it back into the house after the sun set, as the air in the house cooled. Unfortunately, this cannot be devised as an aquarium as the fish could not take the variations in temperature. A huge water tank, with the possibility of leakage, may not be the route most people would take to heat their homes.

Earth is free and readily available. The ever increasing number of tires in need of disposal is a world-wide problem. Think back to the beginning of this unit. It was the thought of all those automobile tires that will eventually become trash and the fact that some type of sustainable housing in the Chinese countryside could stem the flow of people into the already overcrowded cities that launched my desire to create this unit. To quote Reynolds, "You've got dirt and tires. Here's structure, here's mass and here's a heating system — and it's free. . .Thermal mass is usually expensive. Traditional houses have no mass [34]." While insulation helps to keep heat inside houses, it does nothing to store heat. Because it does not hold temperature, we continually heat or cool the air. This results in higher energy and emissions costs [35]. Reynolds decided to pack or ram earth into used tires. He knew that a denser thermal mass would hold and provide more heat [36]. This part of the construction is very labor intensive. Sledge hammers are used to pound an average of 300 pounds of earth into each tire [37]. They are then laid in courses just like those used to lay conventional bricks (see Figure 4). These tires are used to build the interior and back walls. At a width of 30 inches, they provide stability and thermal mass. This thick anchoring mass will absorb solar heat during the day and release it at night.

Figure 4. Reprinted with permission of the publisher from Earthship, Volume I: How To Build Your Own by Michael E. Reynolds: Solar Survival Press

To increase the heat retaining capacity of the house, it is bermed into the earth. The

house ends up looking like it is partially buried from the back towards the front. This, however, is not an underground home. Earthships are airy and open to the outside. By burying the sides and back, or north side, of the house, the thermal mass of the home is increased. By placing the foundation, which is hard-packed earth, below the frost line, the house can maintain a constant temperature no matter what the weather is like outside. At a depth of approximately four feet, the thermal constant of the earth is between 55 and 60 degrees F. For this reason, the tire walls are not insulated away from the earth. "By tapping into this natural thermal constant, the Earthship is consistently comfortable, because this is only 10 degrees away from the North American comfort zone of 70 degrees F [38]." In winter, the solar gain warms the house to a higher temperature if desired during the daytime. Meanwhile, the walls are recharging like a battery. If the house becomes too warm, there are air vents which are used to control temperature. At night, as the house temperature cools, the walls release stored heat. After several cloudy days, backup heat can be provided by a small propane heater or fireplace if desired. But the temperature in the house will not drop below the earth's thermal constant temperature. In summer, this constant temperature helps to keep the house cool.

In the spaces between the tires, where they curve towards each other, beverage cans are inserted as filler along with mud. The mud is used in the same way that cement would be used. Here again, the earth provides a free, renewable, and nonpolluting building material. Electrical wires are run between the courses of tires before plastering begins. Stucco wire covers the tire walls and they are plastered over with plaster, stucco, or mud. If using mud, the same traditional technique used to plaster over adobe bricks is used. The mud is stabilized with sand and bits of straw and can be painted. A flat roof is placed over the structure and a greenhouse is added to the front, or south facing wall. Vertical or angled glazing (glass windows) covers the front of the building where the solar gain will take place. As stated earlier, it is important that the longest axis of the house faces south. Through the use of its space and thermal mass provided by the tire walls, the entire house serves as a battery to store heat in winter [39].

An important aspect to building an Earthship, or any type of home heated by passive solar energy, is to provide enough thermal mass to heat the living space. Therefore, Reynolds recommends that rooms not be larger than 18x26 feet [40]. His layouts use oval or U-modules to form each room. If the living area is too large in relationship to the thermal mass of the walls, then the home may not be able to retain and later radiate enough heat to make it through the night when the sun's energy is not present. Each room acts as a battery storing and releasing heat. The open end of the U faces south, allowing the sun to warm the interior during the day as the walls absorb and store heat. Access between rooms is through an open hallway along the south wall fronting the greenhouse area and south facing windows.

Now the fun begins. The exterior may look like something from Star Wars, but the interior of an Earthship can be quite beautiful and creative (see Figure 5). The curves provided by the tires mean there do not have to be any sharp edges along the walls. Old bottles (more recycling), tiles, and stone can be embedded in the plaster to make beautiful

Figure 5. Reprinted with permission of the publisher from Comfort in Any Climate by Michael E. Reynolds: Solar Survival Press.

works of built-in art. While a single story is the most efficient and least expensive design, it is possible to build multi-level homes. By using cement and recycled beverage cans as bricks, interior walls and stairways take on curved and exotic shapes. Videos of a Taos home called Angels Nest and actor, Dennis Weaver's Colorado home, listed in the bibliography, are excellent examples of how creative one can become with this type of construction. More conventional Earthship designs can be viewed on the Earthship Biotecture web site. This site also has plenty of interior photographs.

With beauty comes function. Reynolds has incorporated all aspects of modern life into the Earthships. It is possible to be totally disconnected from the grid and still have all of the modern conveniences. The following paragraphs describe water systems. While this discussion strays from the solar functions, it describes an important aspect of total sustainability. Other solar innovations will be studied in detail as a part of our classroom activities.

Water from our homes generally flows into a sewer system or septic tank after it is used. Not everyone can hook up to a city sewer system. Septic tanks are expensive to install and have to be periodically cleaned out. There is the hidden danger that water tables close to the surface may become contaminated. There are areas of the world where it is difficult to live due to the scarcity of water. Earthships are capable of capturing water from the sky and reusing it for maximum efficiency.

Where does the water come from if a home is not connected to the utility grid? Digging a well is a possibility. This is another major expense and there is no absolute guarantee that one is going to strike water. Pumping the water up from the well involves more expense and electrical usage. In his book, Water From the Sky, Reynolds details options for collecting and storing rain water and snow melt. For people living in dry areas or in underdeveloped nations his ideas present viable options for leading a sustainable life. Based on Reynolds calculations, it is estimated that in the United States the average water usage per person/per day is 52 gallons. This is based on toilet usage, showers, faucets, dish washer, washing machine and a small amount of leakage [41]. By using the techniques he has developed for the Earthship, an individual's daily water consumption can drop down to approximately 19 gallons. In areas of water scarcity, that is a substantial savings. These savings are achieved by using some of the water more than once.

In an Earthship, the roof area acts as a catchment system, funneling the rain water and/or snow melt towards the first filtration step which is a silt catch device. This will take out any debris which has gathered on the roof. From there it flows into a cistern for storage. The cisterns are usually constructed of tires and located next to the house. This forms a circular structure which appears to be an artistic and integral part of the Earthship. From the cistern, the water flows through a series of filters where it becomes potable and on into a pressure tank. This is the same type of pressure tank used when bringing water up from a well and will require a small amount of electricity. From the tank, it flows through to the conventional system of pipes and faucets [42].

Water used in the home is separated into greywater and black water. The water from a toilet is considered black water. It cannot be reused. For homes not connected to a sewage system there are composting toilets available for purchase. Some of these do use a small amount of electricity. You learned earlier that eliminating even the smallest electrical usage is important. Reynolds has developed a sun powered composting toilet which can be built by the owner. The sun heats solid waste (without smell entering the home) until it turns to ashes which can then be added to a flower garden. This may not seem appealing, but it eliminates the need to dig a septic tank and makes it possible to live in areas with little water. The high temperatures of the process kill off microorganisms. This type of low-tech treatment could go a long way towards improving public health in third world countries.

Greywater is what comes from the sinks, shower, bath tubs, and washing machines. In an Earthship this water is reused. This is why it is possible to live in a dry area, such as the mesas of Northern New Mexico with an annual precipitation of perhaps 8 inches per year, and still have enough water for domestic usage. Here again, the implications for adaptation to underdeveloped countries is significant. Let's follow the greywater as it leaves the kitchen sink or shower. The water drains into a botanical cell which will usually be located in the greenhouse area. The cell is a rubber lined pit with layers of gravel, dirt and plants [43]. As the water filters through the cell, it nourishes the plants, some of which will provide food for the inhabitants, and eventually flows through a filter and into a pipe where it is reused to flush the toilet (if a composting toilet is not being used). The water can be used three times before being sent out to a leach field and or septic system [44]. With the solar, self composting toilet reducing human waste to sterile ashes, the need for a septic system is eliminated and the leach field becomes a minor expense. The plants in the interior botanical cell will grow lavishly, even in winter, absorb CO ₂ and provide oxygen as they filter the air. This function helps to lessen the carbon footprint of the systems within the Earthship. By reusing the water, it is possible to parlay 8 inches of annual precipitation into a usable amount of 24 inches [45]. Because the black and greywater are separated, the greywater when it finally leaves the house can be channeled into another outside botanical cell adding a fourth usage to the water. It should be noted that some municipalities may not allow this type of system within their building codes. In such cases, the Earthship would need to hook into a septic or sewer system.

Earthships have been adapted for use all over the world. In sites where runoff, possible flooding, or a high water table are present, alternative plans are available for building on or above grade. In warmer climates, the large windows are turned north, since heat gain is not an issue. Air conditioning can be achieved by introducing warm, outside air into underground cooling tubes where the temperature is dropped to the earth's thermal constant before being circulated through the house [46]. Reynolds has also developed more contemporary designs, which can be viewed on his website, for those wishing to fit into the urban environment. In April of 2007, the city of Brighton, England approved plans for a sixteen unit development in the heart of the city.