|Fig. 1: Heat map that shows that an older house loses by far more heat due to worse insulation than a passive house. (Source: Wikimedia Commons)|
The consumption of fossil fuels has allowed for human civilization to progress at an accelerated rate. These fuels are the basis for the gasoline in our cars, trucks, and planes, we use them to generate power for illumination and electronic devices or to heat our homes. However, using fossil fuels comes with the cost of pollution, acid rain, and greenhouse gasses which contribute to global warming. In addition to that, energy is one of the most profitable and volatile markets. Thus, it makes sense to reduce our energy consumption and our dependence on fossil resources from both an economic and an environmental perspective. In countries that do not have significant oil deposits, such as Germany, governments, energy companies, and entrepreneurs shift away from fossil resources and towards renewable energies. However, shifting from fossil to renewable energy is not the only way to improve the ecological footprint of our society. If we can reduce the amount of energy that we consume by increasing energy efficiency, then we can reduce our footprint without limiting ourselves in our daily routines. For example, in 2002 the German government released an Energy Saving Ordinance that required all private and commercial buildings to fulfill energy requirements to receive a building license.  Interestingly, a whole new market developed worldwide that focuses on the commercialization of highly energy-efficient houses.
Because the term "low-energy house" was never defined, its meaning is ambiguous and in addition to that a confusing amount of energy classifications for houses exist. Most of them are based on the energy consumption per square meter per year. A famous example is the passive, which has a maximum space heating requirement of 15 kWh/m2 per year. [2-4]
For highly energy-efficient houses, insulation is of paramount importance. With three-pane windows, state of the art insulation methods for walls, roofs and doors, the insulation of these new energy saving houses is so efficient that it becomes a problem. Together with the heat, humidity is trapped within the houses and can cause mold. Thus, air-conditioning with heat-exchangers are an essential and expensive element for low-energy houses. Other methods used to save energy are the strategic positioning of houses relative to the sun, dynamic shading to optimize solar gain for different weather conditions and green roofs. [3,5] In addition, architects are making an effort to design homes such that natural light can be used for illumination throughout the whole house. Furthermore, more and more people rely on sustainable ways to generate their own energy: water gets heated with solar thermal or geothermal energy and power can be generated with photovoltaic systems.
Although fossil fuel consumption is still reality, transitioning to highly energy efficient houses with a smaller ecological footprint provides a solution towards sustainable living. After high initial costs, homeowners are promised certain protections from the turbulent energy market and the homes consume by far less energy than traditional homes. Although the concept has already proved its capabilities, there is still plenty of room for improvements. The final step might be the autonomous house, a vision of Brenda and Robert Vale, who describe it as a "house with no bills." 
© Constantin Dory. 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.
 "Gesetz zur Einsparung von Energie in Gebäuden, Juris, 2013.
 W. Feist et al., "Climate Neutral Passive House Estate in Hannover-Kronsberg: Construction and Measurement Results," Passivhaus Institut, 2005.
 L. Thompson et al., "Green Building Standards," Physics 240, Stanford University, Fall 2015.
 N. Rahman, "Conservation at its Best: The Passivhaus," Physics 240, Stanford University, Spring 2010.
 T. Strobel, "The Zero Energy Home," Physics 240, Stanford University, Fall 2015.
 B. Vale and R. Vale, The New Autonomous House: Design and Planning for Sustainability (Thames & Hudson, 2002).