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To achieve minimal energy use, the design and construction of zero energy buildings departs significantly from conventional building practice. 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. Furthermore, these buildings make use of heat energy that conventional buildings typically let go to waste by use of heat recovery ventilation and hot water heat recycling units. 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.
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