Zero Carbon Housing and Zero Energy Housing are terms used interchangeably to define single family dwellings with a very high energy efficiency rating. Zero Energy Housing requires a very low amount of energy to provide the daily needs and functions for the family occupying the home.
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A zero carbon home has a yearly net carbon footprint of zero. The carbon footprint is the total measure of all greenhouse gas emissions generated or produced directly or indirectly by activities in the home such as heating the home or running an appliance, personal activities such as driving a car, broader services such as the use of public transportation or air travel, and individual consumption of food and other products. A home’s carbon footprint consists of the sum of two parts, the primary footprint and the secondary footprint, expressed in units of metric tonnes of carbon dioxide equivalent(CO2e). The primary carbon footprint is a measure of the CO2 emissions from the direct consumption of fossil fuels for energy consumption and transportation. The secondary carbon footprint is the measure of indirect CO2 emissions related to the manufacturing process of products used in the home and eventual decomposition of products. Examples of the parts that make up the secondary carbon footprint are the manufacturing of clothes, cars, and furnishings, as well as recreational activities by the inhabitants.
The calculation of the carbon footprint becomes detailed when considering secondary factors. Secondary factors involve the home’s occupant lifestyle such as diet, foods are consumed (example organic vs. non organic), frequency of yearly air travel, commuting mileage to and from work, school, etc., use of public transportation, and number, type, and use of private vehicles. Secondary factors also include fashion or type of clothes purchased and worn, frequency of recycling, recreational activities and use of financial and other services throughout a given year. The frequency of airline flights in a year is considered due to the amount of fuel consumption and other energy usage and emissions generated by one flight. A person that travels frequently may have a significantly bigger carbon footprint than someone who flies once a year for a vacation. The emissions for an individual flight are calculated by using the greater circle method. First, the distance between airports is determined. Then calculations are completed to account for indirect distances and by an emissions factor in relation to the type of flight (international or a short flight, and what class seating the person is in). Another contributing factor to a person’s carbon footprint is their personal vehicle which includes the type of car driven, the efficiency or miles per gallon (MPG) rating, and the amount of miles driven each year. The frequency of public transportation used by an individual, miles traveled on public transportation and the type of public transportation used such as bus, train, or subway contributes to their carbon footprint as well. Other factors, as trivial as they might seem, are included in the calculation of a person’s carbon foot print to include things such as the type of diet. A vegetarian compared to a person that eats a lot of red meat will have a lower carbon footprint. All factors being the same except diet, a vegetarian secondary carbon footprint averages three metric tonnes of CO2, one tonne less than the individual who consumes meat. Other factors include the purchase of local and /or organically grown produce vs. imported items, the latest clothes fashions vs. more conventional purchases, buying individually packaged products vs. buying in bulk, recycling activities, and the types of recreation such as carbon-free activities like hiking and cycling or carbon-intensive activities like skydiving or boating.
Determining a Zero Carbon Home
Various private entities and government agencies are beginning to promote the concepts of zero carbon homes and zero carbon footprints. In the United Kingdom the Zero Carbon Hub helped the building of Zero Carbon Housing become a more common practice. The Zero Carbon Hub existed from the summer of 2008 until 31 March 2016 when the government closed it. The Zero Carbon Hub was a public/private partnership working together with the private industry and the government to help reach the government’s energy consumption reduction goals set by the European Union under the Kyoto Protocol of 1997. In the European Union, buildings are responsible for 40% of the total amount of energy needed by the European Union. This percentage is expected to rise with an increase in future building construction.
Despite UK being involved in pioneering some definitions of Zero Carbon Homes, it now appears that it will become unacceptable to market such homes using the term "Zero Carbon Home", because the UK's Advertising Standards Authority (ASA) have ruled that nothing which is manufactured can be called Zero Carbon.
Earthship Biotecture
An example of Zero Carbon Housing is Earthship Biotecture. Developed by Mike Reynolds, the Earthship is an environmentally friendly 100% sustainable type of home that can be built anywhere and in fact have been constructed all over the world. They are constructed with materials that would normally be discarded to take up space in a landfill including old tires, bottles, and cans. Reynolds has three requirements for Earthships. One, a sustainable architecture using natural (non-manmade) materials as well as recycled materials is utilized. Second, dependency on natural energy sources only ("Off-the-grid") and third, be financially feasible and a do-it-yourself concept so an average person could build their own Earthship.
Reynolds’s design was fairly simple. A southward-facing slope is used and partially excavated to nestle the back of the house into the earth and provide a thermal mass along with usage of discarded tires and earth for the walls. The tires are packed with dirt to make a very dense-like brick. These "tire bricks" are strong enough to support the load of a roof structure and also very resistant to fire. Recycled cans and bottles are used as filler in the walls, sometimes with the bottles placed strategically to give an inlay glass tile look.
Earthships use water four times before it is discarded. There are cisterns at roof level to collect rain water or snow melt. The cistern for a given Earthship is sized to the local climate. From the cistern the water is fed into a water-organizing module with a pump and filtering device. The water is pumped into a pressurized tank to meet the building code of required water pressure. This water is used for bathing, drinking, and activities like washing dishes. The water from these activities that is discarded is known as "gray water" and is used in the flushing of the toilets. "Gray water" is not sanitary for drinking but used for other uses in the Earthship. The gray water passes through a grease filter and then into an interior botanical cell. A botanical cell is an indoor garden with growing vegetation. Oxygenation, transpiration, filtration, and bacteria cleansing all take place in the closed cell which cleans and filters the water. After the botanical cell the process of filtering the "gray water" is complete and the water is used to flush the toilets. The state the water is in after being used in the toilet is known as "black water". "Black water" is not reused inside the Earthship but is transferred to a solar-enhanced septic tank with leach fields and used for watering of exterior botanical cells (landscape plantings).
Earthships also have the capacity to process the wastes (generated daily by a household) in the interior and exterior of the Earthship. The exterior botanical cells reduce the waste volume leaching into the ground and reduce the risk of contaminating an aquifer. This system eliminates the use of large public sewer systems and treatment facilities that sometimes cannot adequately treat. The reuse of gray water to produce food allows the Earthships to take sustainability to the next level.
The design of the Earthship structure into the side of a slope allows for maintaining a relatively constant climate inside the home with minimal energy usage. The earthen walls act as a thermal mass soaking up heat during the day and radiating heat into the interior at night. The heat is stored in the mass from the earth walls - when there is no more heat the stored heat radiates to the colder space. This allows the temperature of the inside of the house to stay stable throughout the day and night. Conversely, in warmer ambient temperatures, the earth-bermed house maintains a comfortable indoor temperature assisted by the relatively stable core temperature of the earth.
Earthships can live "off the grid" meaning they can produce their own electricity instead of having to rely on the current infrastructure for power. A power system that consists of photovoltaic cells and a wind power unit supply the Earthship with enough power for the daily actions/usage within a given household. The power from the wind and the solar system is stored in several deep-cycle batteries that deliver the power to the outlets as well as all of the appliances.
Role in Environmental Governance
Zero Carbon Homes and Earthships can play a considerable role in environmental governance. These structures are capable of serving the same everyday functions of a home against changing environmental conditions and are a form of engineering resilience. Engineering resilience is a part of adaptive governance. Adaptive governance is the idea that sustainability can be achieved by adapting to changes instead of changing something completely. Zero Carbon homes allow humans to adapt to the increasing global temperature. These types of homes make it possible for people to survive without the use of declining levels of fossil fuels, protects the inhabitants from food shortages, and water contamination. Zero carbon homes can provide resilience to the changes from the upset of a tipping point in dynamic stability. In this case "tipping point" represents the dangerous aspects of climate change. When a tipping point occurs the system would be subjected to a new domain of stability and the characteristics of stability will have changed. The system will have entered into a new "domain of attraction" and the system will be attracted to a new resting place. In the idea of this, the height of the valley that the "domain of attraction" is in determines the amount of stress or disturbances needed to force the system into another valley or "domain of attraction". Zero carbon homes provide engineering resilience to this event because they will be able to cope with the disturbances that occur. Exactly when these "tipping points" are going to occur is almost impossible to know and difficult to predict. They represent non-linear change, making it difficult to predict or prepare for.