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Designing And Building A Zero Carbon Home Construction Essay

Taking a holistic approach to the minimization of carbon emissions from a building by taking action to:

Ensure energy efficiency.

Use micro-generation and low or zero carbon energy technologies to move toward energy self-sufficiency of the building.

Definitions often ignore the prickly issue of the carbon emissions caused by the sourcing of materials and the construction of the building and its supporting infrastructure. A genuinely zero carbon building will pay back the carbon invested in its construction through exporting zero carbon energy back into the national grid.

In this research we believe that this definition of a genuine zero carbon house is the most appropriate. The payback of invested carbon and the aspiration to move toward negative carbon buildings (buildings that have exported more zero carbon energy back into the national grid than was expended in construction) are cornerstones of our zero carbon building definition.

What is a zero-carbon home?

What exactly is a zero-carbon home?

A zero-carbon home is one that returns to the National Grid as much power as it uses over the course of a year. Unless you plan on living somewhere with no heating, electricity or water, that means a zero-carbon home will need to be kitted out with equipment for micro generation – the production of energy on a small scale.

So, in come mini-wind turbines, solar panels and a wood pellet burner for generating energy. Meanwhile, to keep that precious energy in you will need clever, draught excluding construction with super-insulated walls, a geothermal heating system extracting heat from the ground and triple-glazed windows. You might also want a rain water collecting tank to supply the washing machine and lavatories and to be connected to a reed-bed sewage system for organically cleaning human waste.

The zero-carbon recipe

Design Consultants Arup have suggested a number of innovations:

• Triple-glazing, filled with special gas such as argon, which maintains room temperature. Pipes carrying cool, recycled water instead of air-conditioning.

• More water-efficient washing machines and improved boilers.

• Systems that can recycle 65% of household water by using water from sinks, showers and washing machines for flushing toilets and watering gardens.

Definitions of Zero Carbon

The zero carbon building produces no Carbon Dioxide and by combining all the available innovations can actually export carbon free energy back into the electricity grid.

There are other definitions of buildings that inform any classification, the Zero Carbon Building takes its place amongst them:

Zero Heat Building

Comfortable interior temperatures are maintained through insulation and draft proofing, with no additional heat source. The heat provided by the occupants, appliances, the sun and lighting is sufficient for ordinary requirements.

Zero Carbon Building

A zero heat building when supplied with electricity and additional heating from renewable sources becomes a zero carbon building. It must produce zero net emissions of carbon-dioxide over its lifetime.

The Autonomous Building

Take a zero CO2 building; remove it from mains services (gas, water, electricity and sewage) provide it with electricity generation, sewage processing and water collection solutions (all of which are renewable, sustainable and ecologically sound) and you have an autonomous building.

A redefinition of Zero Carbon

According to the UK Housing and Planning minister Margaret Beckett the meaning of ‘zero carbon’ now needs to be re-evaluated.

“We need a revolution in the ways in which we plan, design and construct our buildings.

“They currently account for nearly half of all our carbon emissions. If we could improve construction methods, the ways in which we heat, light and power our homes, then we would make huge strides towards our overall ambitions.”

So perhaps the suggestion is that we walk before we run that we in the UK start small and become more efficient as a beginning. I’m not sure that necessitates a new definition of zero carbon, but appreciate that in light of the political goal of all new homes being ‘zero carbon’ by 2016 the politicians may want one.

To make it achievable, there are various ways to build the “Zero Carbon Houses”; they can be summed up as: -

Energy generation - Photovoltaic Cells

A photovoltaic (PV) cell is an electronic device that converts solar energy into electricity.

The (very) basic process is:

Photons in sunlight hit the cell and are absorbed by the semiconducting materials (usually silicon) from which the cell is made.

These photons collide with atoms in the cell and in doing so electrons are loosened.

The electrons flow through the material and produce electricity.

PV cells are bundled together and through some very clever technology the low voltage electricity generated by the cells is converted to a higher voltage for use in appliances.

PV cells are able to utilize both direct light and indirect sunlight and so, contrary to popular myth are effective even under grey overcast skies.

There are then three options of what to do with the generated electricity:

Use it to power electrical appliances!

Store it locally - ‘batteries required’.

Export it to the national grid - removing the need for battery storage.

Pros and Cons

Pros (+)

A typical domestic installation in the UK will save around 1.2 tons of carbon dioxide per year

No emissions of CO2 so renewable and sustainable

No moving parts therefore minimal maintenance

Cons (-)

Require a open roof (within 90 degrees of South) that is able to support the substantial weight of the system

High cost - currently around £10,000 for a typical domestic installation in the UK

Energy generation - Wind Turbines

A wind turbine converts the power of the wind hitting the rotor blades of the turbine into rotational force that is converted into electrical energy by a generator.

In the UK relatively large turbines are required for anything other than minor applications - to provide the power for a medium sized home requires a 5 meter diameter rotor blade that is capable of generating around 5kw of power. This will need to be sited in a relatively clear location with an open vista, clear of buildings, trees and other potential barriers. Costs are likely to be between £10,000 & £20, 0000.

Power output increases approximately eight times for a doubling in wind speed so a good location is vital.

Although many micro-generation methods are now permitted developments, planning permission is still required in the UK for wind turbines (although it is expected that this will change).

Once generated, there are then three options of what to do with the generated electricity:

Use it to power electrical appliances!

Store it locally - ‘batteries required’.

Export it to the national grid - removing the need for battery storage.

You can read more on these options - energy storage options

- Pros and Cons

Pros (+)

A typical domestic installation in the UK will save around 1.2 tons of carbon dioxide per year.

No emissions of CO2 so renewable and sustainable.

Cons (-)

Moving parts! - can break!

High cost - currently around £10,000 for a typical domestic installation in the UK.

UK Planning permission required - can be a lengthy expensive process.

Energy storage options

For a truly Zero Carbon solution, we will need to aim for self-sufficiency (or a partial-self-sufficiency) in relation to the electrical energy that we consume. We must couple our energy generation system(s) with a storage system. Current options for what we do with the power we generate are:

Use it to power electrical appliances! - ‘no batteries required’.

Store it locally - ‘batteries required’.

Export it to the national grid - removing the need for battery storage.

Regardless of the type of electricity generation system we choose any electricity not immediately used will need to be stored for future usage.

Batteries are a thorny issue as storage using batteries is an anathema to good environment design. This is because batteries contain toxic metals and unless they are discarded and reprocessed appropriately can easily lead to hazardous waste. Unless for truly off-grid situations, where few viable alternatives exist, batteries are best avoided.

That leaves us with exporting generated electricity to the national grid. These systems remove the need for battery storage. The generation system is connected to the local electricity network (grid) and any electricity not consumed locally can be sold to the electricity supply company. Where the local generation system is unable to provide all electricity demanded, for example at night, then electricity is bought from the grid. The ‘grid’ acts as the storage system. These systems avoid the risk of wasting unused power and also provide a back-up system that ensures that supply is maintained even when the local system is unable to fulfill demand.

PassivHaus

The PassivHaus (German for passive house) standard is the leading standard for energy efficient construction. Despite its name, the standard is applicable to all types of building. The standard was derived in Darmstadt in Germany, in 1990 with the Passivhaus-Institut being setup in 1996 to develop and promote the standard.

The PassivHaus standard aims to provide comfortable year round living conditions through minimal energy expenditure. This is achieved through:

An effective passive solar design that will provide the necessary heat gain (heating).

Coupled with this, to manage the heat gain:

very highly specified effective insulation,

Almost complete air tightness (highly specified triple glazed windows, sealed joints and air barriers are key to this).

Mechanical ventilation coupled with highly efficient heat recovery and ‘backup’ heating systems to manage the internal climate.

The PassivHaus standard defines maximum energy consumption levels, these are:

Heating & Cooling: 15kWh per m2 floor area per annum.

Total Primary (externally sourced) Energy Consumption: 120kWh per m2 floor area per annum for all appliances, domestic hot water and heating and cooling.

Super Insulated Buildings

Key to zero carbon building design is insulation. To minimize energy consumed in heating the volume of the building, insulation should he highly specified and as efficient and effective as possible.

There are varying categories of super insulated buildings.

 

Zero Heat Building

Through highly specified insulation and draft proofing the Zero Heat Building, requires no additional heating, except for in extreme conditions. The heat provided by the occupants’ bodies, household appliances, the sun and artificial lighting is sufficient to maintain a comfortable temperature during normal occupancy. Typically such buildings require triple glazed windows and doors, insulation of 500mm of cellulose fiber the roof, 300mm of expanded polystyrene in the floor, and a 250mm filled wall cavity.

 

Zero CO2 Building

A Zero Heat Building when supplied with power and heating from renewable sources becomes a Zero CO2 Building. A further important criteria is that it must produce zero net CO2 emissions over its lifetime.

 

The Autonomous Building

Remove a Zero CO2 Building from mains gas, water, electricity and sewage services, provide it with a method of electricity generation, sewage disposal and water collection solutions (all of which are renewable, sustainable and ecologically sound) and you have an autonomous building.

- Do these homes exist?

Zero-carbon homes do not widely exist at the moment but there are some aspiring to a carbon neutral life dotted around, housing pioneering environmentalists or architects. There are four developments in London, including a small building, BowZED, in East London and BedZED, in South London, created for the Peabody Trust Housing Association, which has 82 homes designed as zero-carbon. BedZED was finished in 2001/2 but there have problems with its zero-carbon status reported since, meaning extra power has had to be used to heat it and provide energy. Plans have also been unveiled by Aberdeen-based builder Stewart Milne group for a home that meets the zero-carbon criteria.

A semi-detached house in St Albans, Hertfordshire, has been billed as Britain's greenest house, with wind turbine, a roof covered with grass-like plants to keep heat in, and other environmentally friendly measures.

The Zero Carbon House

The Zero Carbon House is a massively intelligent project being funded by the folks at Energy for Sustainable Development in Scotland. The house is being built using all Scottish wood; it will be powered by two on site wind turbines with flow evened by a fuel cell storage unit. All heat will come from heated by air-to-water heat pumps and passive solar. The house will even produce food for its residents in an on-site greenhouse.

Design and construction OF A MODEL ZERO CARBON HOUSE:

The most cost-effective steps toward a reduction in a building's energy consumption usually occurs during the design process. To achieve efficient energy use, zero energy design departs significantly from conventional construction practice. Successful zero energy building designers typically combine time tested passive solar, or natural conditioning, principles that work with the onsite assets. Sunlight and solar heat, prevailing breezes, and the cool of the earth below a building, can provide day lighting and stable indoor temperatures with minimum mechanical means. ZEBs are normally optimized to use passive solar heat gain and shading, combined with thermal mass to stabilize diurnal temperature variations throughout the day, and in most climates are super insulated All the technologies needed to create zero energy buildings are available off-the-shelf today. Sophisticated 3D computer simulation tools are available to model how a building will perform with a range of design variables such as building orientation (relative to the daily and seasonal position of the sun), window and door type and placement, overhang depth, insulation type and values of the building elements, air tightness (weatherization), the efficiency of heating, cooling, lighting and other equipment, as well as local climate. These simulations help the designers predict how the building will perform before it is built, and enable them to model the economic and financial implications on building cost benefit analysis, or even more appropriate - life cycle assessment.

Zero-Energy Buildings are built with significant energy-saving features. The heating and cooling loads are lowered by using high-efficiency equipment, added insulation, high-efficiency windows, natural ventilation, and other techniques. These features vary depending on climate zones in which the construction occurs. Water heating loads can be lowered by using water conservation fixtures, heat recovery units on waste water, and by using solar water heating, and high-efficiency water heating equipment. In addition, day lighting with skylights or solar tubes can provide 100% of daytime illumination within the home. Nighttime illumination is typically done with fluorescent and LED lighting that use 1/3 or less power than incandescent lights, without adding unwanted heat. And miscellaneous electric loads can be lessened by choosing efficient appliances and minimizing phantom loads or standby power. Other techniques to reach net zero (dependent on climate) are Earth sheltered building principles, super insulation walls using straw-bale construction, and exterior landscaping for seasonal shading.

Zero-energy buildings are often designed to make dual use of energy including white goods; for example, using refrigerator exhaust to heat domestic water, ventilation air and shower drain heat exchangers, office machines and computer servers, and body heat to heat the building. These buildings make use of heat energy that conventional buildings may exhaust outside. They may use heat recovery ventilation, hot water heat recycling, combined heat and power, and absorption chiller units.

To conclude the efficacy of our project, we; hereby, mention the advantages and dis advantages of this design: -

Advantages and disadvantages

Advantages

isolation for building owners from future energy price increases

increased comfort due to more-uniform interior temperatures (this can be demonstrated with comparative isotherm maps)

reduced requirement for energy austerity

reduced total cost of ownership due to improved energy efficiency

reduced total net monthly cost of living

improved reliability - photovoltaic systems have 25-year warranties - seldom fail during weather problems - the 1982 photovoltaic systems on the Walt Disney World EPCOT Energy Pavilion are still working fine today, after going through 3 recent hurricanes

extra cost is minimized for new construction compared to an afterthought retrofit

higher resale value as potential owners demand more ZEBs than available supply

the value of a ZEB building relative to similar conventional building should increase every time energy costs increase

future legislative restrictions, and carbon emission taxes/penalties may force expensive retrofits to inefficient buildings

Disadvantages

initial costs can be higher - effort required to understand, apply, and qualify for ZEB subsidies

very few designers or builders have the necessary skills or experience to build ZEBs possible declines in future utility company renewable energy costs may lessen the value of capital invested in energy efficiency

new photovoltaic solar cells equipment technology price has been falling at roughly 17% per year - It will lessen the value of capital invested in a solar electric generating system - Current subsidies will be phased out as photovoltaic mass production lowers future price

challenge to recover higher initial costs on resale of building - appraisers are uninformed - their models do not consider energy

climate-specific design may limit future ability to respond to rising-or-falling ambient temperatures (global warming)

While the individual house may use an average of net zero energy over a year, it may demand energy at the time when peak demand for the grid occurs. In such a case, the capacity of the grid must still provide electricity to all loads. Therefore, a ZEB may not reduce the required power plant capacity.

Without an optimized thermal envelope the embodied energy, heating and cooling energy and resource usage is higher than needed. ZEB by definition do not mandate a minimum heating and cooling performance level thus allowing oversized renewable energy systems to fill the energy gap.

Solar energy capture using the house envelope only works in locations unobstructed from the South. The solar energy capture cannot be optimized in South facing shade or wooded surroundings.

(Figure 1 – Zero Carbon House)

Therefore, there are basic principles to be followed when designing such a project:

The basic principles that can be followed for designing zero energy homes are described in the My Home fact sheets and include:

Incorporating energy efficiency strategies with renewable energy options from the outset of the project.

Choosing a site or location that allows for renewable energy opportunities and reduces transportation and food production needs.

Maximizing passive design strategies in the design of the home to reduce energy demand.

Reducing water use in conjunction with reducing the demand for hot water.

Selecting materials use appropriately, by incorporating materials that enhance the passive design strategy and have a low embodied energy.

Reducing energy use in all areas of the home.

Maximizing energy efficiency allows energy needs to be met with reduced amounts of energy needing to be supplied. Renewable energy opportunities then become:

Physically viable with reduced space requirements.

Economically viable with a reduced amount of renewable energy source being required; and

Environmentally viable with less resources being used to manufacture the renewable energy source.

The expected sources of energy to be used are: -

Embodied energy

Embodied energy is the total energy used to create a product including all the processes involved in harvesting, production, transportation and construction. It can represent a significant proportion of the total energy used during the lifecycle of a home.

Consequences (or impacts) of particular materials and construction systems are often not apparent because they often occur long distances from where the product is used.

This fact sheet outlines some cost effective ways to reduce the embodied energy of materials. These include using construction systems appropriate for climate, substituting materials with high recycled content, and using materials made from new or nonrenewable sources.

Waste minimization

This fact sheets examines methods for lowering costs and reducing consumption of materials by minimizing waste and recycling or re-using materials.

It focuses on the design and construction phases as these are the stages of the lifecycle where the greatest inefficiencies exist and the greatest gains can be made.

Biodiversity Off-site

Biodiversity is the variety of all life forms – the different plants, animals and micro-organisms, the genes they contain and the ecosystems of which they form a part. Biodiversity is an essential human life support system.

The harvesting of many materials used in building a home may cause many adverse impacts on biodiversity including:

Extinction of species.

Destruction of natural systems and habitat.

Degradation of life support systems.

Fragmentation of habitat and populations.

These impacts are rarely apparent at the point of purchase or use. As a result, we continue to specify and use materials that destroy our life support systems, even where alternatives exist.

Construction systems

This fact sheet guides the selection of systems with lowest economic and environmental cost.

It examines the performance of various roof, wall and floor systems in a range of climates and compares their costs and benefits.

Choosing an appropriate system for climate and location will increase thermal comfort, lower construction and maintenance costs and reduce the overall environmental impact.

More detail on construction systems is provided in the following fact sheets:

Mud Brick (Adobe)

Rammed earth (Pisé)

Straw Bale

Lightweight timber

Clay Brick

Autoclaved aerated Concrete (AAC)

Concrete Slab Floor

Green roofs and Walls

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