Zero Energy Buildings

A zero energy building [ZEB] is one with a net energy consumption of zero over a typical year in terms of:

• Energy cost
• Energy consumption
• Carbon emissions

Energy balance requires both energy generation and energy conservation. In calculating the net energy rating, consideration must be given to emissions generated in the construction of the building and energy embodied in the structure which can invalidate claims of reducing carbon emissions.

Some buildings even produce a surplus of energy to requirements. These are known as 'energy-plus' buildings.

In practice, there are a wide range of energy ratings applied to buildings:

Net zero cost - where the price of energy from offsite sources equates to income from sales of electricity to the grid of electricity generated on-site.

Net zero site energy use - the amount of energy provided by on-site renewable energy sources equals to the amount of energy used by the building.

Net off-site zero energy use - energy used by the building is purchased from offsite, 100% renewable energy sources.

Net zero primary energy use - accounts for the inefficiency of off-site generated energy, particularly electricity. Electricity is only around 35% efficient, and further losses [7.2%-7.4%] occur during transmission. Hence, to reach a zero definition for primary energy use, the amount of electricity exported must be substantially higher than the amount of energy brought in.

Net zero energy emissions - also known as a zero carbon building or zero emissions building. Carbon emissions generated from on-site or off-site fossil fuel use are balanced by the amount of on-site renewable energy production.

Off-the-grid - an autonomousself-sufficient Zero Energy Building that is not connected to any off-site energy supply. This requires both renewable energy generation and energy storage capability.

Balancing energy conservation and point-of-use renewable energy generation [solar energy, wind energy, etc.] is hotly debated. The aim of most zero energy designers is to design a building that:

• Uses zero energy
• Produces zero emissions
• Minimises all energy use
• Minimises damge to the environment

The debate is around which element is more important than the others. Regardless of individual opinion, more important is the understanding that a zero energy building does not result from a single product or technology, but rather a group of closely-integrated technologies. Thus design must be approached from a whole-house energy-consumption perspective. Each component must work efficiently and cost-effectively with all other parts, to achieve maximum energy savings, as well as the living needs of the occupants.

Annual net energy bills, and contribution to pollution are only partial measures of zero energy building success. Wider acceptance of zero energy building technology will likely require more government incentives or building code regulations, as well as development of recognised standards.

The World Business Council for Sustainable Development has launched a major initiative to support the development of ZEB.

Zero Energy Building versus Green Building

The goals of ZEB and Green Building are both congruent and disparate.

ZEB design criteria involve major reduction, and eventual elimination of, energy bills and greenhouse gas emissions.

Green building aims to reduce the impact of new buildings on the environment, while improving environmental sustainability. Green architecture, sustainable design, and natural building all embrace similar goals and solution concepts.

Detailed knowledge of zero energy design is less common than Green Building, with many design and building certification programs deficient in coverage in these areas. In addition, computer models used to evaluate Green Building design do not include the thermal science and architectural design patterns necessary to evaluate passive solar building design or zero energy design.

Once constructed, most ZEBs are very “green,” but very few Green Buildings are off-the-grid, or use zero energy. Governments are slowly developing minimum performance standards that recognize the availability of zero-energy technologies for high-performance energy-efficient buildings.

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