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.

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 nuclear power, fuel imports, and the use of fossil fuels in general, and providing a measure of protection against increased future energy prices.

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, but one that also minimises all energy use, irrespective of the fact that 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 sizeable 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.

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 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.

[edit] Design and construction
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.

[edit] 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.

For zero energy building to wide acceptance is likely to require government support or regulation, the development of recognised standards, or significant increases in the cost of energy.

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

Potential advantages of ZEB
it appears to isolate the buildings' occupant(s) from energy price increases
buildings built using ZEB concepts tend to be more comfortable due to more uniform interior temperatures (this can be demonstrated with comparative isotherm maps)
it is substantially less expensive 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

Potential disadvantages of ZEB
first costs can be expected to be higher in the near term
possible significant declines in future energy costs could strand capital invested in energy efficiency
new technology in the field of solar cells could strand capital invested in a solar electric generating system
challenge to recover higher first costs on resale of building
passive design may limit future ability to respond to rising ambient temperatures

In the media
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

References
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

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