Zero-energy building

A zero energy building (ZEB) or net zero energy building is a general term applied to a building with zero net energy consumption and zero carbon emissions annually. Zero energy buildings are autonomous from the energy grid supply - energy is produced on-site. This design principle is gaining considerable interest as renewable energy is a means to cut greenhouse gas emissions. Buildings use 40% of the total energy in the US and European Union.^[1][2]

Contents 1 Overview 2 Definitions 3 Design and construction 4 Energy generation 5 The "energy generation" versus "energy conservation" debate 6 Occupant behavior 7 The modern evolution of zero energy buildings 7.1 Influential zero- and low-energy buildings 7.2 New-generation ZEBs 7.3 ZEB development efforts 8 Zero energy building versus green building 9 Zero-energy buildings worldwide 9.1 Canada 9.2 Germany 9.3 Ireland 9.4 Malaysia 9.5 Norway 9.6 United Kingdom 9.7 United States 9.7.1 Examples 10 Advantages and disadvantages of ZEBs 10.1 ZEB advantages 10.2 ZEB disadvantages 11 See also 12 External links 13 References 14 Further reading

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 could be seen as invalidating the claim of zero energy. So much energy is used in the construction of a new building that this can dwarf the energy saved over its useful life. The definitions below provide a useful clarification of how to further classify zero energy buildings, and show that a zero net energy building can still be improved upon.

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.

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 source energy use

This ZEB generates the same amount of energy as is used, including the energy used to transport the energy to the building. This type accounts for losses during electricity transmission. These ZEBs must generate more electricity than net zero site energy buildings.

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

In this type of building, the cost of purchasing energy is balanced by income from sales of electricity to the grid of electricity generated on-site. Such a status depends on how a utility credits net electricity generation and the utility rate structure the building uses.

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).

Design and construction

The most cost-effective energy reduction in a building usually occurs during the design process.^[4] 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 on site assets. Sunlight and solar heat, prevailing breezes, and the cool of the earth below a building, can provide daylighting and stable indoor temperatures with minimum mechanical means. Z.E.B.'s 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 superinsulated.^[5] All the technologies needed to create zero energy buildings are available off-the-shelf today.

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, natural ventilation, and other techniques. These features can vary drastically between buildings in different climate zones. Water heating loads can be lowered using water conservation fixtures, heat recovery units on waste water, and by using solar water heating, and high-efficiency water heating equipment. In addition, free solar daylighting with skylites or solartubes can provide 100% of daytime illumination. Nighttime illumination is typically done with fluorescent and LED lighting that use 1/3 or less of the power of incandescent lights, without adding unwanted heat that incandescent lights do. 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, superinsulation walls using strawbale construction, and exterior landscaping for seasonal shading.

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, combined heat and power, and absorption chiller units.

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.

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, export electricity to the grid when there is a surplus, and drawing electricity when not enough electricity is being produced. Other buildings may be fully autonomous.

Generation is most often more effective (in cost and resource utilisation) when done on a local scale eg a group of houses, co-housing, local district, village, etc. rather than an individual basis.

Zero Energy Production, in commercial and industrial applications. Taking into account the diverse topography of each location and designing a renewable energy development approach to satisfy the production energy required to develop each product. This production energy always reduces the profitability of each facility constructed in the future. With Zero Energy Production comes the arena of placing Geothermal, Microhydro, Solar, and Wind resources to lower the initial impact of each facilities requirement to be self sustainable using only sustainable energy.

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 or net zero energy use cities, such as the planned Dongtan Eco-City near Shanghai or Masdar City in Abu Dhabi in the United Arab Emirates.

A benefit of such localized energy generation (note localised as apposed to individual) is the elimination of electrical transmission and electricity distribution losses. These losses amount to about 7.2%-7.4% of the energy transferred.^[6]

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.^[7]

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^[8] and other locations where photovoltaic (PV) subsidies are significant,^[9] 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) ^[10], and also requires greater embodied energy and greater resources and is thus the lesser ecological approach..

For three decades, passive solar building design and Passive house has demonstrated heating 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 photovoltaic panels on the roof of a conventional inefficient building.^[10] A few kilowatt-hours of photovoltaic panels (costing tens of thousands of U.S. dollar equivalent) may only reduce external energy requirements by 15% to 30%. A 100,000 BTU (110 MJ) high seasonal energy efficiency ratio 14 conventional air conditioner requires over 7 kW of photovoltaic 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 photovoltaic electricity then becomes more cost-effective.

Occupant behavior

The energy used in a building can vary greatly depending on the behavior of its occupants. Studies of identical homes in the United States have shown dramatic differences in energy use, with some homes using more than twice the energy of others.^[11] Occupant behavior can vary from differences in setting and programming thermostats, varying levels of illumination and hot water, and the amount of miscellaneous electric devices used.^[4]

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.

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 ^[12] 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 ^[13].^[14]

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 modest energy efficiency, and a big distributed renewable energy generation from both solar and wind. Designed by Skidmore Owings Merrill LLP in Guangzhou, China^[15], 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.^[16][17] Opened and occupied as of October 2007, this San Jose, California building was designed by EHDD Architecture 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. http://z2building.com/mainpage.html

Googleplex, Google's headquarters in Mountain View, California, completed a 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).

Hudson Valley Clean Energy in Rhinebeck, NY has proven it is zero net energy. 15 kW of solar pv, geothermal heating and cooling and air tight construction allow this building to generate more energy than it consumes to heat, cool and power the building. After one year of operation the unassuming metal building generated more than 110% of total energy consumption.

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 photovoltaic campus, and the Microsoft 480-kilowatt photovoltaic campus relied on U.S. Federal, and especially California, subsidies and financial incentives. California is now providing $3.2 billion USD in subsidies ^[18] 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.^[19] The Florida Solar Energy Center has a slide presentation on recent progress in this area.^[20]

The World Business Council for Sustainable Development ^[21] 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.^[22]

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.^[23] Zero energy buildings achieve one key green-building goal of completely or very significantly reducing energy use and greenhouse gas emissions for the life of the building. Zero energy buildings may or may not be considered "green" in all areas, such as reducing waste, using recycled building materials, etc. However, zero energy, or net-zero buildings do tend to have a much lower ecological impact over the life of the building compared with other 'green' buildings that require imported energy and/or fossil fuel to be habitable and meet the needs of occupants.

Because of the design challenges and sensitivity to a site that are required to efficiently meet the energy needs of a building and occupants with renewable energy (solar, wind, geothermal, etc), designers must apply holistic design principles, and take advantage of the free naturally occurring assets available, such as passive solar orientation, natural ventilation, daylighting, thermal mass, and night time cooling.

The US LEED Green building certification does not require a building to have net zero energy use, only to reduce energy use a few percentage points below the minimum required by law. And, many Green building certification programs (such as the Leadership in Energy and Environmental Design developed by the U.S. Green Building Council, and Green Globes, all involve evolving check lists that are measurement tools, not design tools. Inexperienced designers or architects may cherry-pick points to meet a target certification level, even though those points may not be the best design choices for a specific building or climate.

Zero-energy buildings worldwide

Canada

In Canada the Net-Zero Energy Home Coalition ^[24] is an industry association promoting net-zero energy home construction and the adoption of a near net-zero energy home (nNZEH), NZEH Ready and NZEH standard. The Canada Mortgage and Housing Corporation is sponsoring the EQuilibrium Sustainable Housing Competition^[25] that will see the completion of fifteen zero-energy and near-zero-energy demonstration projects across the country starting in 2008. The Now House Project, which is a retrofit of a postwar home in Toronto, Ontario. The Riverdale project is a duplex near Edmonton, Alberta, completed in 2008. ^[26] The EcoTerra TM House in Eastman, Quebec, is Canada's first nearly net zero-energy housing built through the CMHC EQuilibrium Sustainable Housing Competition. ^[27] The house was designed by Dr. Masa Noguchi of the Mackintosh School of Architecture for Alouette Homes and engineered by Prof. Dr. Andreas K. Athienitis of Concordia University. ^[28] Dr. Athienitis and his research group have also participated in the design of the Hudson, Quebec Alstonvale Net Zero House project^[29], led by the Montreal-based architect Sevag Pogharian.

Germany

Technische Universität Darmstadt won first place in the international zero energy design 2007 Solar Decathlon competition, with a passivhaus design (Passive house) + renewables, scoring highest in the Architecture, Lighting, and Engineering contests ^[30]

• Self-Sufficient Solar House Fraunhofer Institute for Solar Energy Systems(ISE), Freiburg im Breisgau

^[31]

Ireland

In 2005 Scandinavian Homes^[32] launched the worlds first standardised passive house in Ireland, this concept makes the design and construction of passive house a standardised process. Conventional low energy construction techniques have been refined and modelled on the PHPP (Passive House Design Package) to create the standardised passive house. Building offsite allows high precision techniques to be utilised and reduces the possibility of errors in construction.

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 kW·h/day. The renewable energy - photovoltaic 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.^[33]

Norway

In February 2009, the Research Council of Norway assigned The Faculty of Architecture and Fine Art at the Norwegian University of Science and Technology to host the Research Centre on Zero Emission Buildings (ZEB), which is one of eight new national Centres for Environment-friendly Energy Research (FME). The main objective of the FME-centres is to contribute to the development of good technologies for environmentally friendly energy and to raise the level of Norwegian expertise in this area. In addition, they should help to generate new industrial activity and new jobs. Over the next eight years, the FME-Centre ZEB will develop competitive products and solutions for existing and new buildings that will lead to market penetration of zero emission buildings related to their production, operation and demolition.

United Kingdom

In the English region of 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 Wales the plan is for the standard to be met earlier in 2011, although it is looking more likely that the actual implementation date will be 2012.

• The Hockerton Housing Project

United States

In the U.S., ZEB research is currently being supported by the US Department of Energy (DOE) Building America Program ^[34], 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.^[35]

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.^[35]

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^[36] 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^[37] DOE/ORNL Workshop materials include an 800-page eBook, 500 presentation slides, and related support materials.

New Leaf America, founded by zero-energy pioneer Chris Prelitz, offers a web based, climate specific roadmap for U.S. homeowners. Weatherization, behavior change, conservation, efficiency, and passive solar strategies are identified to ready homes for the most efficient renewable system needed to offset total energy demand.

Examples

• zHome is a 10 unit zero energy community utilizing detailed energy modeling to achieve true zero net energy, located in Issaquah, WA. Key zero energy features of zHome include a hyper insulated shell, ground source heat pump for heating and hot water, and photovoltaic panels. This project is scheduled for completion at the end of 2009. zHome is believed to be the first production, multifamily, fully zero net energy community in the United States. ^[38]

• The 31 Tannery Project, located in Branchburg, New Jersey, serves as the corporate headquarters for Ferreira Construction, the Ferreira Group, and Noveda Technologies. The 42,000-square-foot (3,900 m²) office and shop building was constructed in 2006 and is the 1st building in the state of New Jersey to meet New Jersey's Executive Order 54. The building is also the first Net Zero Electric Commercial Building in the United States.

• The Audubon Center at Debs Park, Los Angeles is an example of an off-the-grid zero energy building that relies on extensive energy efficiency strategies combined with solar thermal and photovoltaic renewable energy systems to supply its energy needs.

• The Putney School's net zero Field house was opened October 10 2009. The building features sun tracking solar panels, recycled floors, and maple walls, and floors that were harvested locally, and on Putney School grounds. It is the first net zero school building. In the summer The Field House produces more energy than it consumes, The Putney School will sell the extra energy back to grid.

Advantages and disadvantages of ZEBs

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 - photovoltaic systems have 25-year warrantees - 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

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 to build ZEBs ^[39]
• 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 optimised 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 concept cannot be optimized in South facing shade or wooded surroundings.

See also

External links

• The Alstonvale Net Zero House
• The Now House Project
• US Department of Energy Building America
• www.ornl.gov - Oak Ridge National Laboratory (ORNL) Building Technology
• www.FSEC.UCF.edu - Florida Solar Energy Center
• zHome - Issaquah, Washington, USA
• The Research Centre on Zero Emission Buildings, Norway
• Palo Alto Net Zero Energy House - The Palo Alto Net Zero House is the green renovation of a home in Palo Alto, California. Completed in June 2009, the house is net zero energy. It creates energy with a photovoltaic solar array panel. It saves energy with a hydronic HVAC, EnergyStar appliances, and improvements to its building envelope. The renovation's website teaches home owners and building professionals about green renovations.
• The Putney School Zero Energy Field House - Completion scheduled for September 2009. No performance data as yet.

References

Notes

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
• Noguchi, Masa, ed., "The Quest for Zero Carbon Housing Solutions", Open House International, Vol.33, No.3, 2008, Open House International