Zero Energy Building

A zero energy building (ZEB) 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.

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 such 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, because so much energy is used in the constructon of a new building that this can dwarf the energy saved over its useful life.

Design and construction

The most cost-effective energy reduction in a building usually occurs during the design process. 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. 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 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.