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A zero energy building (ZEB) or net zero energy building is a general term applied to a building with a net energy consumption of zero over a typical year. This can be measured in different ways (relating to cost, energy, or carbon emissions) and, irrespective of the definition used, different views are taken on the relative importance of energy generation and energy conservation to achieve energy balance.

Although zero energy buildings remain uncommon in developed countries, they are gaining in importance and popularity. The zero-energy approach is seen to be a potential solution to a range of social and environmental issues, including reducing carbon emissions, reducing dependence on oil power, fuel imports, and the use of fossil fuels in general, and providing a measure of energy security against future energy crises.

A building approaching zero energy use may be termed a near zero energy building or ultra-low energy building. Those that produce a surplus of energy may be known as energy-plus buildings.

Contents 1 Definitions 1.1 Net zero cost 1.2 Net zero site energy use 1.3 Net zero energy use 1.4 Net zero primary energy use 1.5 Net zero energy emissions 2 The energy generation - energy conservation debate 3 Energy generation 4 Design and construction 5 The development of zero energy building 5.1 Canada 5.2 United States 5.3 United Kingdom 6 Potential advantages of ZEB 7 Potential disadvantages of ZEB 8 Technology 9 See also 10 In the media 11 References 12 Further reading

Despite sharing the name 'zero energy building', there are several definitions of what this means in practice, with a particular difference in usage between North America and the rest of the world.

At the simplest level, 'net zero energy' relates to the price of energy. In such a building, the cost of purchasing energy is balanced by income from sales of electricity to the grid of electricity generated on-site. Whether this balance can be maintained over the medium to long term is subject to fluctuations in energy prices. To distinguish it from other types of zero energy building, the term net zero energy cost building may be used.

In this type of zero-energy building, the amount of energy provided by on-site renewable energy sources is equal to the amount of energy used by the building.

This variation of zero-energy building considers that purchasing energy used by the building from 100% renewable energy sources, even if the energy is generated off the site, is sufficient to constitute a zero-energy building.

More sophisticated than the previous definitions, the zero primary energy building or zero energy source building recognises that the off-site generation of energy, particularly electricity, is very inefficient. Typically only around 35% of the energy used in a conventional fossil fuel power plant is converted to electricity, with the remainder lost as waste heat. Further losses accumulate during electricity transmission. Because of this, in order to meet the definition of zero primary energy use, the amount of electricity exported must be substantially higher than the amount of energy registered on the electricity meter.

Outside the United States and Canada, a net zero energy building is generally defined as one with zero net energy emissions, also known as a zero carbon building or zero emissions building. Under this definition the carbon emissions generated from on-site or off-site fossil fuel use are balanced by the amount of on-site renewable energy production.

A variation of this definition includes not only the carbon emissions generated by the building in use, but also those generated in the construction of the building and the embodied energy of the structure. Others debate whether the carbon emissions of commuting to and from the building should also be included in the calculation.

One of the key areas of debate in zero energy building is over the balance between energy conservation and the use of renewable energy.

To the majority of zero energy designers, the aim of zero energy building is not only to design a building that, on balance, uses zero energy or produces zero emissions, but one that also minimises all energy use, irrespective of the fact that the energy may come from renewable resources. This approach can perhaps best be seen in the German Passivhaus standard.

However, while recognising that energy conservation has a part to play, a significant body of designers consider that it is of lower importance and instead rely to a greater extent on 'active' techniques (solar power, wind turbines, etc.) to make up the energy / heat shortfall.

In the case of individual houses, various microgeneration technologies may be used to provide heat and electricity to the building, perhaps using solar cells or wind turbines for electricity, and biofuels, or solar collectors linked to seasonal thermal stores, for space heating. To cope with fluctuations in demand, zero energy buildings are frequently connected to the electricity grid, and may export electricity to it when there is a surplus. Others may be fully autonomous (off-grid) buildings.

Zero-energy neighbourhoods, such as the BedZED development in the United Kingdom, may use distributed generation schemes combined with district heating. There are currently plans to use similar technologies to build entire zero-energy cities, such as Dongtan near Shanghai.

To achieve minimal energy use, the design and construction of zero energy buildings departs significantly from conventional building practise. In conventional building design the emphasis is normally on minimizing construction costs. Designers rarely do any energy analysis or lifecycle operating cost calculations beyond those necessary to comply with local building codes.

In the ZEB approach every decision about major sub-system selection is evaluated in terms of its future consequences on energy demand using life cycle energy analysis. ZEB designers are usually prepared to increase construction costs if doing so will reduce energy demand and operating costs by an equal or greater amount. The ZEB approach might be described as "energy first" building design.

In addition to using renewable sources, zero energy buildings are also designed to make use of energy gained from other sources including white goods, lighting, and even body heat. They are normally optimised to use passive solar heat gain, use thermal mass to even out temperature variations throughout the day, and in most climates are superinsulated. All the technologies needed to create zero energy buildings are available off the shelf today.

Designers typically use sophisticated computer simulation tools to take into account a wide range of design variables such as building orientation (relative to the sun), window type and placement, overhang depth, insulation values of the building elements, air tightness, the efficiency of heating, lighting and other equipment, as well as local climate. These simulations help the designers to know how the building will perform before it is built, and enable them to model the financial implications on building cost.

The development of zero energy buildings has been made possible not only through the progress made in new construction technologies and techniques, but has also relied on academic research on traditional and experimental buildings in order to generate the data for the computer models.

The zero energy building concept can be seen as a progression from other low-energy building techniques. Amongst these, the Canadian R-2000 and the German passive house standards have been influential. Government and internationally sponsored demonstration projects such as the first superinsulated Saskatchewan House, and the International Energy Agency's Task 13 have also played their part. And, in particular, the many enthusiastic private individuals who commissioned houses using cutting edge low energy technologies has been vital.

One of the first ZEB office buildings is the 69 story Pearl River Tower which will open in 2009 as the headquarters for the Guangdong Tobacco Company. This building takes advantage of both high energy efficiency and generation from both solar and wind to create a ZEB design. The Skidmore Owings Merrill LLP project is currently under construction. Economic support from government subsidies has been used to help fund the project.

For zero energy building to achieve wide acceptance is likely to require government support or regulation, the development of recognised standards, or significant increases in the cost of energy. The World Building Council for Sustainable Development has launched a major initiative to support the development of ZEB. Led by the CEO of United Technologies and the Chairman of LaFarge (large cement producer/polluter see www.emccement.com for a production process that uses 50 percent less cement) , the organization has both the support of large global companies and the expertise to mobilize the corporate world and governmental support to make ZEB a reality.

In Canada the Net-Zero Energy Home Coallition is an industry association promoting zero energy home construction. Recently the Canada Mortgage and Housing Corporation sponsored a public competition that would see the construction of twelve to sixteen zero energy demostration projects across the country by the end of 2007. The final competition winners will be announced at the end of February 2007.

In the USA ZEB research is currently being conducted by Jeff Christian and others at Oak Ridge National Laboratory (ORNL).

In the United Kingdom, in December 2006 the Government announced their 'ambition' that, by 2016, all new homes will be zero energy buildings. To encourage this, an exemption from Stamp Duty Land Tax is planned. Whilst some organisations have applauded the December 2006 pre-budget statement from the UK Chancellor, Gordon Brown, others challenge the motives and the governments ability to deliver on the promise [1]. The voluntary AECB Gold Standard sets rigorous criteria for such buildings.

See energy efficiency in British housing.

• potential isolation of buildings' occupant(s) from energy price increases
• increased comfort due to more uniform interior temperatures (this can be demonstrated with comparative isotherm maps)
• reduced cost to improve energy efficiency during initial design and construction than it is to do so through a retrofit
• higher resale value
• the value of a ZEB building relative to similar conventional building increases as energy costs increase

• initial costs can be higher
• possible significant declines in future energy costs could strand capital invested in energy efficiency
• new solar cells technology could strand capital invested in a solar electric generating system
• challenge to recover higher initial costs on resale of building
• passive design may limit future ability to respond to rising or falling ambient temperatures

After the construction of the Glaspaleis in the Netherlands, it was found that the construction of glass and concrete collected and stored so much solar energy that much less heating was needed, even though that was a side-effect (the goal of the glass was maximum entry of sunlight).

• Arcology
• Passive house
• Superinsulation
• Solar cell
• Insulation
• Weatherization
• Active solar
• Thermal conductivity (for an explanation of thermal conductivity, thermal conductance, and thermal resistance)
• Thermal mass
• Earth sheltering
• Earthship
• Energy-efficient landscaping
• Environmental design
• Life cycle energy analysis
• Natural Building
• Renewable energy
• Autonomous building
• Straw-bale construction
• Peak oil
• Sim Van der Ryn
• Steve Baer
• Ecopolis (city)
• Low-energy house
• Green building
• EnerGuide for Houses
• Environmental economics

• February 2002, Energy Design Update, "Zero Energy Homes Face Marketing Hurdles"
• September 2002, Oak Ridge National Laboratory & Building America to Build a Zero Energy House
• July 2004, Energy Design Update, "Getting Down to Zero"
• April 2006, Mid-Atlantic PowerHouse Showcases Energy Efficiency

• Common Fire Foundation Comprehensive Overview of Green Building, plus info on the net-zero energy "Greenest Building in the Eastern US" (non-profit)
• Oak Ridge National Lab (ORNL)
• Download 2000 ZEB meeting report
• Zero Energy House - NAHB Research Center
• "Self-Sufficient Solar House " Fraunhofer Institute's (ZEB), Freiburg, Germany
• ecoLogical Home Ideas Magazine for green home building/remodeling

Nisson, J. D. Ned; and Gautam Dutt, "The Superinsulated Home Book", John Wiley & Sons, 1985, ISBN 0-471-88734-X, ISBN 0-471-81343-5. Markvart, Thomas; Editor, "Solar Electricity" John Wiley & Sons; 2nd edition, 2000, ISBN 0-471-98853-7.

Clarke, Joseph; "Energy Simulation in Building Design", Second Edition Butterworth-Heinemann; 2nd edition, 2001, ISBN 0-7506-5082-6.

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