Zero-energy building

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BedZED zero energy housing in the UK
BedZED zero energy housing in the UK

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. Zero energy buildings are gaining considerable interest as a means to cut greenhouse gas emissions and conserve energy. Buildings use 40% of the total energy in the US and European Union.[1][2]

Contents

[edit] Overview

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 issues, including reducing carbon emissions, and reducing dependence on fossil fuels. Most ZEB 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 called a near-zero energy building or ultra-low energy house. Buildings that produce a surplus of energy during a portion of the year may be known as energy-plus buildings. An energy autarkic house is a building concept where the balance of the own energy consumption and production can be made on an hourly or even smaller basis. Energy autarkic houses can be taken off-the-grid.

[edit] Definitions

Despite sharing the name 'zero energy building', there are several definitions of what ZEB means in practice, with a particular difference in usage between North America and Europe. [3]

Net zero site energy use
In this type of ZEB, the amount of energy provided by on-site renewable energy sources is equal to the amount of energy used by the building. In the United States, “zero energy building” generally refers to this type of building.
Net zero energy emissions
Outside the United States and Canada, a ZEB 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. Other definitions include 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.
Net zero cost
Consumers are the most interested in this type of ZEB, because 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. 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
Net zero primary energy use
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 off-site zero energy use
A building may be considered a ZEB if 100% of the energy it purchases comes from renewable energy sources, even if the energy is generated off the site.
Off-the-grid
Off-the-grid buildings are stand-alone ZEBs that are not connected to an off-site energy utility facility. They require distributed renewable energy generation and energy storage capability (for when the sun is not shining, wind is not blowing, etc).

[edit] Design and construction

To achieve minimal energy use, zero energy design departs significantly from conventional construction practice. Zero energy building designers typically use sophisticated 3D computer simulation tools to take into account a wide 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.

Zero Energy Buildings are usually built with significant energy-saving features. The heating and cooling loads are often drastically lowered by using high-efficiency equipment, added insulation, high-efficiency windows, passive solar techniques, and other techniques. These features can vary drastically between buildings in different climate zones. Water heating loads can be alleviated by using heat recovery units on waste water, and by using high-efficiency water heating equipment. In addition, lighting energy use can be lessened by daylighting, fluorescent and LED lighting, and miscellaneous electric loads can be lessened by choosing efficient appliances and minimizing standby power. Zero energy buildings are often designed to make use of energy gained from other sources including white goods; for example, use refrigerator exhaust to heat domestic hot water, ventilation air and shower drain heat exchangers, office machines and computer servers, and even body heat from rooms with multiple occupants. These buildings make use of heat energy that conventional buildings typically exhaust outside. They may use heat recovery ventilation, hot water heat recycling, and absorption chiller units. They are normally optimised to use passive solar heat gain, use thermal mass to stabilise diurnal 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.

Other unique energy-saving strategies include using absorption chillers, daylighting, Combined heat and power,[3], and Passive cooling.

[edit] Energy generation

ZEBs generate their own energy to meet their electricity and heating needs. In the case of individual houses, various microgeneration technologies may be used to provide heat and electricity to the building, 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 neighborhoods, such as the BedZED development in the United Kingdom, and those that are spreading rapidly in California and China, may use distributed generation schemes. This may in some cases include district heating, community chilled water, shared wind turbines, etc. There are current plans to use ZEB technologies to build entire off-the-grid cities, such as the PV-powered Huangbaiyu Sustainable Village, and the planned Dongtan Eco-City near Shanghai.

A benefit of such localized energy generation is the elimination of Electrical transmission and electricity distribution losses. These losses amount to about 7.2%-7.4% of the energy transferred.[4]

[edit] The "energy generation" versus "energy conservation" debate

One of the key areas of debate in zero energy building design is over the balance between energy conservation and the distributed point-of-use generation of renewable energy (solar energy, wind energy, etc.). Most zero energy homes use a combination of the two strategies.[5]

As a result of significant government subsidies for photovoltaic solar electric systems, wind turbines, etc., there are those who suggest that a ZEB is a conventional house with distributed renewable energy generation. Entire additions of such homes have appeared in locations such as California[6] and other locations where PV subsidies are significant,[7] but many so called "Zero Energy Homes" still have utility bills. This type of energy generation without energy conservation may not be cost effective with the current price of photovoltaic equipment (depending on the local price of power company electricity) [8], and also requires greater embodied energy and greater resources and is thus the lesser ecological approach..

For three decades, passive solar building design has demonstrated energy consumption reductions of 70% to 90% in many locations, without using any active power generation systems. With expert design, this can be accomplished with little additional new construction cost for materials over a conventional building, but very few industry experts have the skills or experience to do this. Such passive solar designs are much more cost effective than adding expensive PV panels on the roof of a conventional inefficient building.[8] A few kWh of PV panels (costing tens of thousands of U.S. dollar equivalent) may only reduce external energy requirements by 15% to 30%. A 100,000 BTU high seasonal energy efficiency ratio 14 conventional air conditioner requires over 7 kW of PV electricity while it is operating, and that does not include enough for off-the-grid night time operation. Using passive cooling, and superior system engineering techniques, can reduce the air conditioning requirement by 70% to 90%, where PV electricity then becomes more cost-effective.

[edit] The modern evolution of zero energy buildings

The development of modern zero energy buildings became possible not only through the progress made in new construction technologies and techniques, but it has also been significantly improved by academic research on traditional and experimental buildings, which collected precise performance data for today's advanced computer models, and the engineering design decision criteria for the many differences between alternative zero energy design patterns.

[edit] Influential zero- and low-energy buildings

Those who commissioned construction of Passive Houses and Zero Energy Homes (over the last three decades) were essential to iterative, incremental, cutting-edge, technology innovations. Much has been learned from many significant successes, and a few expensive failures.

The zero energy building concept has been a progressive evolution from other low-energy building designs. Among these, the Canadian R-2000 and the German passive house standards have been internationally influential. Collaborative government demonstration projects, such as the superinsulated Saskatchewan House, and the International Energy Agency's Task 13, have also played their part.

The 1999 side-by-side Florida Solar Energy Center Lakeland Florida demonstration project[1] was called the "Zero Energy Home." It was a first-generation university effort that significantly influenced the creation of the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Zero Energy Home program. George Bush's Solar America Initiative is funding research and development into widespread near-future development of cost-effective Zero Energy Homes in the amount of $148 million in 2008[2].[3]

[edit] New-generation ZEBs

One example of the new generation of zero energy office buildings is the 71-story Pearl River Tower, which is scheduled to open in 2009, as the Guangdong Company headquarters. It uses both high energy efficiency, and distributed renewable energy generation from both solar and wind. Built by Skidmore Owings Merrill LLP in Guangzhou, China[9], the tower is receiving economic support from government subsidies that are now funding many significant conventional fossil-fuel (and nuclear energy) energy reduction efforts.

One of the first zero-energy commercial buildings in the United States is Integrated Design Associates (IDeAs) Z-Squared Design Facility.[10][11] Opened and occupied as of October 2007, this San Jose, California building was designed to meet a net-zero-energy/zero-carbon-emissions (Z-squared) target. Notably, it is a remodel of a commonplace 1960’s-era tilt-up concrete structure that once served as a corner bank. Z-squared performance was achieved through simple, affordable strategies, including daylighting, radiant heating, ground source heat pump cooling, advanced insulation and glazing and reduced computer and appliance loads through careful equipment selection and wiring.

Google's Silicon Valley headquarters (in Mountain View, CA) has just completed a huge 1.6 megawatt photovoltaic campus-wide renewable power generation system. Google (and others) have developed advanced technology for major reductions in computer-server energy consumption (which is becoming a major portion of modern zero-energy commercial building design, along with daylighting and efficient electrical lighting systems).

[edit] ZEB development efforts

Wide acceptance of zero energy building technology may require more government incentives or building code regulations, the development of recognised standards, or significant increases in the cost of conventional energy.

The Google PV campus, and the Microsoft 480-kilowatt PV campus relied on U.S. Federal, and especially California, subsidies and financial incentives. California is now providing $3.2 billion USD in subsidies[4] for residential-and-commercial near-zero-energy buildings, due to California's serious electricity shortage, frequent power outages, and air pollution problems. The details of other American states' renewable energy subsidies (up to $5.00 USD per watt) can be found in the Database of State Incentives for Renewables and Efficiency.[5] The Florida Solar Energy Center has a slide presentation on recent progress in this area.[6]

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 percent. Survey respondents estimated that greenhouse gas emissions by buildings are 19 percent of the worldwide total, in contrast to the actual value of roughly 40 percent.[12]

[edit] Zero energy building versus green building

The goal of green building and sustainable architecture is to use resources more efficiently and reduce a building's negative impact on the environment.[13] Zero energy buildings achieve one green-building goal of significantly reducing energy use and greenhouse gas emissions. Zero energy buildings, however, are not necessarily green, because in order to achieve net zero energy use or carbon emissions, buildings do not require other green building practices such as reducing waste, using recycled building materials, etc.

Similarly, green building certification does not require a building to have net zero energy use, only to reduce energy use. Green building council certification criteria (such as the Leadership in Energy and Environmental Design Green Building Rating System, developed by the U.S. Green Building Council) involve evolving check lists that reduce the impact of new buildings on the environment, while improving environmental sustainability. Sustainable architecture, sustainable design, and natural building all embrace similar goals and solution concepts. The computer models used to evaluate green building design do not include the thermal science and architectural design patterns necessary to evaluate state-of-the-art passive solar building design or zero energy design.

One green building limitation is that the potentially-complex thermal physics necessary for zero energy design is not part of the required formal education for professional architects[citation needed]. Thus, the knowledge of zero energy design is less common than the basics of green building[citation needed].

[edit] Zero-energy buildings worldwide

[edit] Germany

Technische Universität Darmstadt won first place in the international zero energy design 2007 Solar Decathlon competition, scoring highest in the Architecture, Lighting, and Engineering contests[7]

"Self-Sufficient Solar House " Fraunhofer Institute's (ZEB), Freiburg, Germany [8]

[edit] Canada

In Canada the Net-Zero Energy Home Coalition[9] is an industry association promoting zero energy home construction. The Canada Mortgage and Housing Corporation is sponsoring the Equilibrium Housing Competition that will see the construction of twelve zero-energy and near-zero-energy demonstration projects across the country by the end of 2008, one of which is a retrofit of a postwar home. The Edmonton project is a duplex in Riverdale, currently at the rough-in stage. [10]

[edit] United States

In the U.S., ZEB research is currently being supported by the US Department of Energy (DOE) Building America Program[11], including industry-based consortia and researcher organizations at the National Renewable Energy Laboratory (NREL), the Florida Solar Energy Center (FSEC), Lawrence Berkeley National Laboratory (LBNL), and Oak Ridge National Laboratory (ORNL). From fiscal year 2008 to 2012, DOE plans to award $40 million to four Building America teams, the Building Science Corporation; IBACOS; the Consortium of Advanced Residential Buildings; and the Building Industry Research Alliance, as well as a consortium of academic and building industry leaders. The funds will be used to develop net-zero-energy homes that consume at 50% to 70% less energy than conventional homes.[14]

DOE is also awarding $4.1 million to two regional building technology application centers that will accelerate the adoption of new and developing energy-efficient technologies. The two centers, located at the University of Central Florida and Washington State University, will serve 17 states, providing information and training on commercially available energy-efficient technologies.[14]

According to Energy Design Update (February 2007), one home 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.

The U.S. Energy Independence and Security Act of 2007[15] created 2008 through 2012 funding for a new solar air conditioning research and development program, which should soon demonstrate multiple new technology innovations and mass production economies of scale.

One of the most comprehensive modern compilations of information on this subject is the U.S. Department of Energy (DOE) Oak Ridge National Laboratory (ORNL) Building Technology group "Thermal Performance of the Exterior Envelopes of Whole Buildings Tenth International Conference" held December 2007. The popular Zero Energy Design[16] DOE/ORNL Workshop materials include an 800-page eBook, 500 presentation slides, and related support materials.

[edit] United Kingdom

Further information: Energy efficiency in British housing

In the United Kingdom, in December 2006 the government announced that by 2016 all new homes will be zero energy buildings. To encourage this, an exemption from Stamp Duty Land Tax is planned. In October 2007 the UK Green Building Council warned that few zero carbon developments were actually being built as the criteria for carbon neutral stamp relief was so stringent.[citation needed]

[edit] Malaysia

In October 2007, the Malaysia Energy Centre (PTM) successfully completed the development and construction of the PTM Zero Energy Office (ZEO) Building. The building has been designed to be a super-energy-efficient building using only 286 kwh/day. The renewable energy - PV combination is expected to result in a net zero energy requirement from the grid. The building is currently undergoing a fine tuning process by the local energy management team. Findings are expected to be published in a year.[17]

[edit] Advantages and disadvantages of ZEBs

[edit] ZEB 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 - PV systems have 25-year warrantees - seldom fail during weather problems - the 1982 PV 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

[edit] Potential ZEB 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 - ZEB supply falls far short of current growing demand
  • 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 PV 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)
  • without an optimised thermal envelope embodied energy and resource usage is higher than needed


[edit] See also

Energy Portal
Sustainable development Portal


[edit] In the media

[edit] External links

  • [12] - US Department of Energy Building America
  • www.ornl.gov - Oak Ridge National Laboratory (ORNL) Building Technology
  • www.FSEC.UCF.edu - Florida Solar Energy Center

[edit] References

  1. ^ Baden, S., et. al., "Hurdling Financial Barriers to Lower Energy Buildings: Experiences from the USA and Europe on Financial Incentives and Monetizing Building Energy Savings in Private Investment Decisions." Proceedings of 2006 ACEEE Summer Study on Energy Efficiency in Buildings, American Council for an Energy Efficient Economy, Washington DC, August 2006.
  2. ^ US Department of Energy. Annual Energy Review 2006 27 June 2007. Accessed 27 April 2008.
  3. ^ a b Torcellini et al. Zero Energy Buildings: A Critical Look at the Definition. National Energy Renewable Laboratory (NREL). June 2006.
  4. ^ Powerwatch. Domestic Energy Use in the UK. 2000.
  5. ^ “Building Science Glossary.” Building Science Consortium. Accessed 27 April 2008.
  6. ^ Clarum Unveils California's First Zero Energy Home Community. 1 April 2003.
  7. ^ Database of State Incentives for Renewables & Efficiency (DSIRE) Home. 2007.
  8. ^ a b P. Eiffert. Guidelines for the Economic Evaluation of Building-Integrated Photovoltaic Power Systems. Prepared for National Renewable Energy Laboratory. January 2003.
  9. ^ Skidmore, Owings & Merrill Pearl River Tower. Retrieved on 2008-04-14.
  10. ^ From Zero to Net-Zero Squared. Archi*tech Magazine. Stamats Business Media (January 2008). Retrieved on 2008-02-04.
  11. ^ The Zero-Zero Hero. IEEE Spectrum. IEEE (September 2007). Retrieved on 2008-02-04.
  12. ^ World Business Council for Sustainable Development, August 2007, Energy Efficiency in Buildings: Business Realities and Opportunities Retrieved: 2007-09-05.
  13. ^ US Environmental Protection Agency, "Green Building," 16 Apr. 2008. Accessed on: 17 May 2008.
  14. ^ a b U.S. DOE - 2007 Solar Decathlon Closing Ceremony and Awards (October 2007.). Retrieved on 2008-04-14.
  15. ^ U.S. Energy Independence and Security Act of 2007. Retrieved on 2007-12-23.
  16. ^ Three Decades Of Zero Energy Design Lessons Learned. U.S. Department of Energy (DOE) Oak Ridge National Laboratory (ORNL) Buildings Technology - "Thermal Performance of the Exterior Envelopes of Whole Buildings Tenth International Conference". Retrieved on 2007-12-23.
  17. ^ PTM Zero Energy Office Building Project. August 2006.

[edit] 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.

National Renewable Energy Laboratory, 2000 ZEB meeting report