Zero carbon housing

Zero Carbon Housing and Zero Net Energy Housing are terms used interchangeably to define buildings with low energy usage that generate all that energy from zero-carbon sources (such as solar panels or wind turbines) located on the property. "Zero net energy" does not mean that a house uses zero energy. All houses use energy for lighting, heating/cooling and electrical appliances. However, a house can use zero net energy if it generates all the energy it uses from zero carbon sources located on site. Zero net energy is typically defined as being for a whole year. https://www.energy.gov/eere/buildings/downloads/common-definition-zero-energy-buildings

Roof-mounted solar panels are the most established way to generate zero-carbon power on site. In practice, Zero Net Energy Housing requires reducing a house's energy use sufficiently that all that energy can be generated by roof-mounted solar panels. A house's energy use can be reduced by increasing insulation, draft proofing, using double or triple-glazed windows and using high efficiency heating sources like heat pumps (either ground-sourced, also known as geothermal, or air-sourced), which can be four times as efficient as heating with a furnace or boiler. Once the houses energy use has been significantly reduced, solar panels can generate all that energy from the roof. Particularly if the roof is facing to the south. Zero Net Energy houses are becoming possible with new construction but are still rare as upgrades to existing houses.

A zero carbon house has a yearly net carbon footprint of zero. The carbon footprint is the total measure of all greenhouse gas emissions generated or produced by that house such as heating the home, cooking and using electricity. A family's carbon footprint (as distinguished from a house's carbon footprint) consists of the sum of two parts, the primary footprint (the carbon footprint of the house) and the secondary footprint. 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. Both the primary and secondary carbon footprint can be expressed in units of metric tonnes of carbon dioxide equivalent (CO2e).

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.

Calculating a family's secondary carbon footprint is very hard to do because the carbon footprint of most purchased products is not readily available.

In contrast, the primary carbon footprint can be calculated directly from the energy bills sent to the house by the utility companies that provide electricity, natural gas, heating oil and propane. For instance, electricity generates approximately 1 pound of CO2 per kilowatt hour, natural gas generates about 0.4 pounds of CO2 per kilowatt hour and heating oil generates about 0.5 pounds of CO2 per kilowatt hour. There are 2000 pounds per ton so pounds of carbon dioxide can be converted to tons of carbon dioxide by dividing by 2000. Fuel data is from the US Energy Information Administration https://www.eia.gov/tools/faqs/faq.php?id=73&t=11 and electricity data is from Eversource which is a large utility company based in Massachusetts. https://www.eversource.com/content/docs/default-source/nh---pdfs/insert_nh_disclosure_label_sep15_web-final.pdf

Standards for determining zero-carbon home and net-zero home: Zero Carbon / Net Zero, Passivhaus, LEED Certification, ZERH, HERS and Greenness

Zero-carbon footprint and net-zero energy

The terms zero-carbon footprint and net-zero energy mean essentially the same thing. Since even a single light bulb uses electricity (which is a form of energy) a house can never use zero energy. However, since you can generate electricity from solar panels it is possible to have a house that generates all of the energy it uses over the course of a year. If you generate enough energy to power your home every single day of the year then you have gone “off grid”. If you generate as much energy as your house uses over the course of a full year, but not every day, then you have a net-zero energy house, which will require a connection to the electrical grid via a net meter so you have power at night.  If the energy used by the house is all generated by zero-carbon sources (such as solar panels or a wind turbine) then the terms net-zero energy and zero-carbon footprint mean the same thing. In theory, if you used a diesel-powered generator to make all the electricity your house used (and that was all the energy your house used) then you would have a net-zero energy house, but this is not usually how the term is used. In common usage a net-zero energy house means a house which generates all its energy on site and that energy is made from zero-carbon sources like solar panels or wind turbines. Hence it is equivalent to a zero carbon house.

PassivHaus (Passivehouse), PHIUS

PassivHaus is a standard for low-energy or zero-energy houses. It was developed in Germany by the PassivHaus Institute. There is a U.S. branch of the PassivHaus Institute called the Passive House Institute US or PHIUS. PassivHaus certification requires compliance to their exacting standards for both building materials and methods of construction as well as the final result in terms of energy efficiency expressed in kilowatt-hours per square meter of floor space. To achieve PassivHaus certification every element of the construction must be audited back to its source. The PassivHaus standard for total energy use is 60 kilowatt-hours per square meter of floor space per year. This is equal to 5.6 kWh per square foot per year. If your house has 2,500 square feet of living space (which is typical in the U.S.) then your total energy budget to meet the PassivHaus standard (including the energy in heating fuel like natural gas or heating oil, plus your electricity use) is about 14,000kWh per year. The average U.S. house uses about 11,000kWh per year in electricity alone. When you add in the extra energy used to heat the home, often five times the amount of energy used in electricity, the average U.S. house uses about 500% more energy than the PassivHaus standard.

Because of the prescriptive details and audit trail on building components required by PassivHaus it is almost impossible to apply it to the renovation of an existing house and PassivHaus certification is only applicable to new construction. It is both expensive and time consuming to do the audit.

LEED (Leadership in Energy and Environmental Design) Certification

LEED Certification is a program of the U.S Green Building Council and is somewhat similar to the PassivHaus standard except it provides more flexibility on reaching overall energy efficiency performance rather than requiring the strict adherence to the prescriptive building elements of the PassivHaus standard. However, LEED does not currently offer a standard for renovating an existing house, it only applies to new construction.

Zero-Energy Ready Home (ZERH) and Home Energy Rating System (HERS)

The U.S. Department of Energy offers its Zero Energy Ready Home (ZERH) program but it is more aimed at certifying builders rather than buildings. Hence, just like the PassiveHaus and LEED programs it is focused on new construction, not how to go zero on your existing home. The ZERH program relies heavily on EnergyStar standards for appliances and windows and the HERS (Home Energy Rating System) for performance. HERS is focused on energy use relative to a benchmark house (i.e., how your home compares to a model house of the same floor area) rather than minimizing energy or spending. A HERS rating is only available on new houses, not for existing ones. A review of the HERS rating system in Home Energy magazine found that, in practice, “there was no clear relationship between the rating score of an individual home and actual energy cost.” See the quoted article here: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-home-s-hers-index-calculated

Greenness

These existing energy efficiency-rating programs have significant drawbacks. None of PassivHaus, LEED or ZERH/HERS quantify either how much you can cut your carbon footprint or how much money you can save, they don’t work on existing houses and are also burdensome and costly to implement usually requiring you to hire experts to do an audit.

Also, none of these standards adjusts the energy used for the climate in which your house is located. An average house in Massachusetts consumes far more energy than an identical house in Arizona simply because it is much colder in winter in Massachusetts than it is in Arizona. A bigger house will consume more energy than a smaller house. There is a need for a new standard that accounts for both the size of a house and the climate in which it is located. Kilowatt-hours (of total energy used) per square foot of living space per heating-degree-day per year has been proposed as the measure of energy efficiency and kilowatt-hours net of on-site zero-carbon energy production per square foot of living space per heating-degree-day per year as the measure of overall greenness. See link here for details: https://greenzerocarbonhome.com/energy-and-finance-terms-explained/net-zero-passivhaus-leed-certification-zerh-and-hers/

Within the USA the heating degree days for your area can be found by entering your zip code at http://www.degreedays.net

How to create a zero-carbon home part 1 – new construction

New homes that have a year-round zero-carbon footprint can now be built by commercial builders. See these examples:

Professor Phil Jones designed this house which was built in 2015 in the U.K.: https://www.bbc.com/news/science-environment-33544831

Farr Associates designed this house which was built in 2011 in Chicago, U.S.: https://www.wired.com/2011/08/green-housing/

Newly constructed homes that have achieved a zero-carbon footprint have these key factors in common:

·      High levels of insulation in the attic, walls and basement

·      High levels of draft proofing. In fact, the houses can be so airtight as to require ventilation pumps to ensure fresh air in the house. Such fresh air ventilation systems often remove the heat from the air that is exiting the house and use it to warm the air that it coming in. These are called heat-recovery ventilators or HRV’s for short.

·      Windows with high-insulation values. E.g, double or triple-pane windows with low-E glazing which can be 700% as efficient at single-glazed windows.

·      Passive solar gain, meaning south facing windows with overhangs or shades that can provide solar gain in the winter but can keep out the solar gain in summer.

·      Heating and cooling with high efficiency systems such as geothermal (ground-sourced) heat pumps or air-sourced heat pumps rather than furnaces. Heat pumps can be about four times as efficient as furnaces for heating a house.

·      Appliances such as refrigerators, clothes dryers and dishwashers that use less energy than normal appliances. A common standard is the U.S. government’s EnergyStar rating system. In particular, modern refrigerators are far more efficient than ones that are more than about 10 years old.

·      LED light bulbs that use far less electricity for the same amount of light than incandescent ones.

·      Solar panels (often mounted on the roof) to generate carbon-free electricity. Wind power can also be used but it is far less common than solar panels.

It is the improvements in many of these technologies such as: heat pumps, solar panels, low-E triple-glazed windows, spray-foam insulation and LED lighting that have made it possible to now create newly built homes that have a primary carbon footprint of zero.

Zero-carbon footprint homes cost about 5-10% more to build than a comparable house built to the existing housing code, but cost less to run as there are lower (or no) heating and electricity bills. The cost of financing the additional 5-10% investment by taking out a larger mortgage is more than offset by the energy savings over time as illustrated here: http://zeroenergyproject.org/buy/cost-less-to-own/

The U.S. builds approximately 1m new houses a year https://www.census.gov/construction/nrc/pdf/compann.pdf

and has approximately 126m houses in total https://www.statista.com/statistics/183635/number-of-households-in-the-us/

So more than 99% of all homes in the U.S. are already built. Hence the real challenge in reducing the country’s carbon footprint is not in designing new homes that are zero-carbon, but in renovating existing home to give them a zero-carbon footprint or at least a greatly reduced carbon footprint.

How to create a zero-carbon home part 2 – upgrading an existing house

A zero-carbon footprint has been achieved on existing homes but it is much rarer than on newly built homes. These examples show how it can be done:

https://greenzerocarbonhome.com/home-page/outlines-of-the-chapters-of-the-book/summary-if-you-only-have-two-minutes-please-read-this/

https://www.fastcompany.com/3046525/in-just-a-week-this-kit-turns-old-houses-into-zero-energy-homes-for-free

http://www.greenbuildingadvisor.com/blogs/dept/musings/high-cost-deep-energy-retrofits

Many aspects of creating a zero-carbon home on an existing house are similar to those for creating a zero-carbon home that is newly built. However, some aspects that are fairly inexpensive on a new home (such as choosing a south facing orientation, using thick insulation on the walls or using triple-glazed rather than double-glazed windows) are far more expensive as upgrades to an existing home. Hence upgrades to an existing home often use only the sub-set of aspects listed above for new construction that pay for themselves when used to upgrade an existing home. Homeowners have found that the following upgrades can pay for themselves (see here for an example):

·      High levels of insulation in the attic and basement. Adding insulation to the walls is typically too expensive to pay for itself with savings on the energy bills.

·      Modest levels of draft proofing such as adding draft proofing strips to windows and doors. Achieving the very high levels of air-tightness seen on newly built zero-carbon homes requires major renovation that is too expensive to pay for itself on an existing home.

·      Windows with high-insulation values such double or triple pane windows with low-E glazing can rarely improve the energy efficiency enough to pay for themselves from the savings on heating bills alone (at least not for decades). However, the additional cost of triple-glazing over the cost of double-glazing can pay for itself, making triple-glazed windows possibly a good investment if the homeowner is replacing windows for other reasons such as because the windows are rotting or the windows are falling apart.

·      Passive solar gain, which is largely determined by the orientation of the house to the sun, is almost impossible to improve significantly in an existing house. However, if the house is overheating due to strong solar gain through the windows, it can be cooled off with pergolas, overhangs and blinds.

·      Heating and cooling with high efficiency systems such as geothermal (a.k.a. ground-sourced) heat pumps or air-sourced heat pumps rather than furnaces. Heat pumps can be about four times as efficient as furnaces for heating a house. This is true for existing homes as well as new homes.

·      Appliances such as refrigerators, clothes dryers and dishwashers that use less energy than normal appliances. A common standard is the U.S. government’s EnergyStar rating system. In particular, modern refrigerators are far more efficient than ones that are more than about 10 years old. This is true for existing homes as well as new homes and appliances are fairly easy to replace.

·      LED light bulbs that use far less electricity for the same amount of light than incandescent ones. This is true for existing homes as well as new homes.

·      Solar panels (often mounted on the roof) to generate carbon-free electricity. This is true for existing homes as well as new homes. Wind power can also be used but it is far less common than solar panels

The total investment (after tax breaks and subsidies) to get an existing home to a zero carbon footprint has been reported as about 5% of the home value. See here . Return on investment was reported as being approximately 15%.

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.

Most people do not have the skills or time to build their home from reclaimed materials. Hence these types of homes remain idealistic examples and they have not been widely implemented.

The Citu Home

Citu, a company working to accelerate the transition to zero carbon cities, has developed a zero-emission home in partnership with Leeds Beckett University, in part funded by Innovate UK . With the goal of creating a system able to be produced at scale to allow mass adoption, the Citu Home is built in a factory from timber-framed panels. The factory is located in the 'Climate Innovation District', an area on the outskirts of Leeds City Centre where 500 zero emission Citu Homes will be built.

The Citu Home was developed using Passive House tools to create a building so efficient that its heating needs will be on average ten times lower than a conventional house. The home does not have a gas boiler, instead it uses a MVHR system to recycle heat from people and appliances. This means the home's small heating requirements can be satisfied entirely with renewable energy. Citu supply all Citu Homes with 100% renewable energy via Good Energy, one of the UK's leading renewable electricity suppliers.

The homes timber framed design allows it to sequester several tonnes of CO2 in the building's structure, whilst the fact it is powered by 100% renewable energy for all its energy needs (including heating) means people living in it can expect to reduce their carbon footprint by over two tonnes of CO2 per year, as the average UK household emits 2.3 tonnes of CO2 heating their home .

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.

Possible Complications

·Affordability: The Net Zero home, can be cheaper in the long run as it has very low (or zero) energy bills. However, it requires an investment in the systems (like insulation, windows and heat pumps) up front that has been reported as being 5-10% of the initial cost of the house. See above sections on both getting a new home and an existing home to a zero-carbon footprint.

·Energy Production: One of the most important factors in the construction a Net Zero structure is the amount of energy it will save in comparison to the previous structure. Any Net Zero building needs to be able to function at the same capacity at which it had prior to the retrofitting. This means that each structure will need to produce enough energy to sustain itself. Net Zero homes are most commonly fitted with solar panels as the main energy production source on the roof of the structure. Solar panels on the roofs of existing and newly built homes are becoming common in places like California, Massachusetts and Germany. These are not necessarily the sunniest places but tend to be the places with reasonable sun plus high electricity prices and generous subsidies. As solar panels have got better and cheaper it has become feasible to generate all the energy a house uses from panels on its roof. However, this is only possible if the house's walls, roof, basement and windows are very well insulated, if its heating system is very efficient (usually meaning heat pumps rather than burning fossil fuels in a furnace or boiler) and it uses very efficient appliances and LED light bulbs.

·Financing: Even though net-zero homes can now cost less in the long run (even including the cost of financing the extra investment in insulation, efficiency and solar power generation) the upfront investment can still be several tens of thousands of U.S. dollars that many families do not have. Recent initiatives by governments, particularly in the U.S., (such as the Massachusetts Solar Loan and Heat Loan programs) have focused on making low-interest or zero-interest loans available to homeowners to attempt to overcome this financing barrier.