|Fig. 1: Solar panels on top of a school building. (Source: Wikimedia Commons).|
Commercial and residential buildings comprise approximately 70% of the energy usage in the United States, and energy consumption in the building sector continues to rise. Between 1980 and 2000, electricity usage for commercial buildings doubled, and is expected to increase by another 25% by 2025.  Consequently, there has been an international effort to decrease commercial and residential buildings' energy consumption has led to the popularity and construction of ZEB's. A ZEB, or a zero energy or zero emissions building, is a commercial or residential building that has efficient energy usage and has reduced energy needs.  The nearly zero or minimal amount of energy required to operate the building should be covered by renewable energy sources on or nearby the site.  The common design goal of a zero energy building is that cheap, local, renewable, nonpolluting sources will allow the building to meet its energy requirements.  To harvest energy, ZEB's make use of wind turbines and solar cells for electricity (see Fig 1), and solar cells and solar thermal collectors for heat.  ZEB's are designed to regulate temperature by maximizing sunlight and solar heat, wind direction, and the cool of the earth. 
|Fig. 2: A zero energy building in Munster, Germany. (Source: Wikimedia Commons)|
Zero energy buildings can be homes, office buildings, schools, etc., and their designs come in many different variations, for example Fig. 2. There are four main types of ZEB's: net zero site energy buildings, net zero source energy buildings, net zero energy costs buildings, and net zero energy emissions buildings. Net zero site energy buildings produce as much energy as it uses, when accounted for at the site, and this can be verified through on-site measurements.  Some examples of energy generators for site ZEB's include roof-mounted photovoltaic cells, small-scale wind power, or solar hot water collectors. A net zero source energy building produces as much energy as it uses relative to the source energy, which is the primary energy created and delivered to the site.  Imported and exported energy is multiplied by a site-to-source conversion multiplier to calculate the building's total source energy. A 3.37 to 1 ratio must be employed for site gas energy use to be balanced with on-site electricity generation.  A zero energy cost building is one where the amount paid to the building owner for the energy exported to the grid is greater than or equal to cost of the energy services for the year.  Lastly, a zero energy emissions building is a building that compensates for its usage of emissions producing energy sources by producing at least as much emissions-free renewable energy. 
With over 40% of the European Union's energy demand stemming from the building sector, the EU has placed an emphasis on energy efficiency policies. In its 2050 roadmap, the EU delineates establishes the goal that member countries overall should cut emissions to 80% by 2050 below the 1980 levels.  In 2016, effort to reduce the energy consumption of buildings, the EU updated its original 2010 Energy Performance of Buildings Directive to say that all new buildings must have either zero or very low energy needs by 2020.  EU member countries must set minimum energy performance requirements for the construction of all new buildings and the renovation of buildings, and countries must determine national financial measures that will improve the energy efficiency of buildings. Additionally, the EU put the Energy Efficiency Directive in place, which mandates that EU governments only purchase highly energy efficient buildings and member countries make energy efficient renovations to at least 3% of the central's governments buildings.  In combination, these efforts should help the European Union lower its energy demands in the future.
© Madie Chou. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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