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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 promoted as 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 Fuel s in general, and providing a measure of Energy Security against future Energy Crises . Most definitions do not include the emissions generated in the construction of the building and the embodied energy of the structure which would usually invalidate claims of reducing carbon emissions. 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 '''. DEFINITIONS 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. Net zero cost 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. For commercial buildings, a cost ZEB is typically the hardest to reach, and is very dependent on how a utility credits net electricity generation and the utility rate structure the building uses (Torcellini et al. 2006). Net zero site energy use 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. Net off-site zero energy use 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. Net zero primary energy use 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 . Net zero energy emissions 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 more honest 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. THE ENERGY GENERATION - ENERGY CONSERVATION DEBATE 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 (perhaps encouraged by the HVAC sector) consider that it is of lower importance and instead rely to a greater extent on 'active' techniques ( Solar Power , Wind Turbine s, etc.) to make up the energy / heat shortfall. ENERGY GENERATION In the case of individual houses, various Microgeneration technologies may be used to provide heat and electricity to the building, perhaps using Solar Cell s or Wind Turbine s for electricity, and Biofuel s, or Solar Collector s linked to Seasonal Thermal Store s, 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) Building s. Efficiency measures such as daylighting or energy conversion like combined heat and power ( CHP ) devices cannot be considered on-site production in the ZEB context. Fuel cells and microturbines do not generate energy; rather they typically transform purchased fossil fuels into heat and electricity. Passive solar heating and daylighting are demand-side technologies and are considered efficiency measures (Torcellini et al. 2006). Zero-energy neighborhoods, 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 . DESIGN AND CONSTRUCTION To achieve minimal energy use, the design and construction of zero energy buildings departs significantly from conventional building practice. 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 Code s. 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. Furthermore, these buildings make use of heat energy that conventional buildings typically let go to waste by use of Heat Recovery Ventilation and Hot Water Heat Recycling units. 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 BUILDING 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 Business 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 , 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. Their first report, a survey of key players in real estate and construction, indicates that the costs of building green are overestimated by 300%, survey respondents put greenhouse gas emissions by buildings at 19 percent of world total, while the actual number of 40 percent is double this. World Business Council for Sustainable Development, August 2007, ''Energy Efficiency in Buildings: Business Realities and Opportunities'' Retrieved: 2007-09-05. Canada In Canada the Net-Zero Energy Home Coalition 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 demonstration projects across the country by the end of 2007. The final competition winners will be announced at the end of February 2007. United States In the USA ZEB research is currently being supported by the US Department of Energy Building America Program (www.buildingamerica.gov), including 5 industry-based consortia and researchers at the National Renewable Energy Laboratory (NREL), the Florida Solar Energy Center (FSEC), Lawrence Berkely National Laboratory (LBNL), and Oak Ridge National Laboratory (ORNL). According to Energy Design Update (February 2007), only one house in the United States has demonstrated 12 months of data showing net-zero-energy performance; that house, located in Wheat Ridge, Colorado, was built by Metro Denver Habitat for Humanity, with help from NREL engineers. United Kingdom In the sets rigorous criteria for such buildings. :See '' Energy Efficiency In British Housing ''. POTENTIAL ADVANTAGES OF ZEB
POTENTIAL DISADVANTAGES OF ZEB
TECHNOLOGY 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 sun''light''). SEE ALSO
IN THE MEDIA
REFERENCES
FURTHER READING 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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