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| Fig. 1: A residential solar installation. (Source: Wikimedia Commons) |
In a world where climate change is unequivocal, governments have implemented steps to reduce emissions and pollutants to the environment. While much attention has focused on mitigating the damage done by automobiles, the home has been largely neglected by the government as a source of pollution. In reality, homes burn more petroleum for heating and electricity than is consumed in the operation of automobiles. [1] The federal government has taken action to minimize the future environmental footprint of its buildings. By Executive Order 13693, beginning in fiscal year 2020 all new construction of Federal buildings greater than 5,000 sq. ft. must be designed to be energy net-zero. As defined in that order, "net-zero energy building means a building that is designed, constructed, or renovated and operated such that the actual annual source energy consumption is balanced by on-site renewable energy." [2] Such scrutiny, if applied to new home construction, could greatly enhance the sustainability of the modern lifestyle. The two main methods of achieving a net-zero energy building are reducing its consumption of energy and producing energy in a renewable manner. By combining a multitude of techniques which reduce energy demand or harness renewable energy, the net-zero energy home can be achieved.
To ensure a house's ability to be a net-zero energy building without relying on external sources, the techniques for power generation that follow pertain solely to on-site supply options. Such methods are ones which can be located within the building footprint or at the building site. [3] The main method for doing so is through the use of solar panels (Fig. 1). In fact, I have yet to come across a net-zero energy building that does not employ the use of photovoltaic electricity. These panels convert energy from the sun into electricity that can be used to power a home. Another resource for renewable energy is on-site wind power. Despite being limited in scale due to their large geographical footprint, wind turbines provide an alternate energy source to solar panels. A third source of on-site energy production is solar hot water systems. Like solar panels, these devices use the energy from the sun to heat water for the occupants of the house. Finally, geothermal heat pumps are an efficient method for heating, air-conditioning and ventilation systems. It uses the relative warmth of the ground in the winter and the relative coldness of it in the summer to maintain a comfortable living environment. These are just some of the many methods that can be used in parallel to power a net-zero energy home.
In order for the above methods to be able to produce enough energy to power a home, improvements in efficiency must also be implemented. In zero-energy buildings, energy demand is up to 68% less than that of buildings constructed under the current code. [4] This is achieved through the use of superior insulation, passive solar building design, lighting improvements and home automation technologies. Better insulation minimizes the load placed on heating and air-conditioning systems. Passive solar design can further improve this efficiency by facilitating natural heating and cooling of a building. Lighting improvements can be made by using LED light bulbs. In addition, smart architectural design can allow for natural daylighting. Home automation technologies can drastically improve the efficiency of both air-conditioning and lighting systems. [5] Products like the Nest Thermostat (Fig. 2) do so and are currently available on the market at reasonable cost. The combination of these technologies sufficiently improves the efficiency of buildings to a level at which they can be net-zero energy compliant.
While the tools for establishing a net-zero energy home are readily available due to modern technological advancement, some environmental and economic challenges remain. Since 2011, the price of solar panels has decreased by 60%. However, the national average up-front cost for a five-kilowatt solar installation remains near $23,000. [6] This is a significant investment with a lengthy payback period for an entry level homebuyer. Climactically, a mild environment is ideal for implementing net-zero energy buildings. This complicates the goal of achieving widespread adoption of this classification. In order for photovoltaic electricity generation, there must be sufficient sunlight to provide energy to the solar panels. Yet, an overly high or low external temperature leads to a higher demand for energy to power heating and air-conditioning systems. Finally, wind power requires a steady source of wind which is only available in certain locations. The success of net-zero energy buildings is enhanced when the environmental conditions are mild and balanced which cannot be guaranteed at all locations. Because of these environmental and economic challenges, governmental action is needed to accelerate the adoption of net-zero energy buildings.
One standard that has been adopted for energy efficient buildings is that of the passivhaus. These are units which can maintain a comfortable interior climate without the use of active heating or cooling systems. [7,8] Yet, the utopian vision of minimizing energy use is difficult to implement in scale due to the demands of modern technology and machinery. A net-zero energy requirement is a much more realistic regulation to place on new home construction. Projects like the Start.Home concept provide a blueprint for large scale adoption of net-zero energy homes. [9] By both minimizing the need for energy and generating it from renewable sources, net-zero energy homes can begin to curtail the environmental impact of houses. This will keep pace with similar reforms aimed at abating the harmful byproducts of the transportation sector. It is undeniable that a complete plan to mitigate the effects of human life on the environment must include the impacts caused within the household.
© Trey Strobel. 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.
[1] E. Evarts, "Cars vs Houses - What Consumes More Energy?," Consumer Reports, 27 Aug 09.
[2] "Executive Order 13693 - Planning for Federal Sustainability in the Next Decade," Federal Register 80, No. 57, 25 Mar 15.
[3] S. Pless and P. Torcellini, "Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options," U.S. National Renewable Energy Laboratory, NREL/TP-550-44586, June 2010.
[4] P. Torcellini, S. Pless, and M. Deru, "Zero Energy Buildings: A Critical Look at the Definition," U.S. National Renewable Energy Laboratory, June 2006.
[5] N. A McNabb, "Strategies to Achieve Net-Zero Energy Homes: A Framework for Future Guidelines Workshop Summary Report," National Institute of Standards and Technology, NIST Special Publication 1140, April 2013.
[6] J. Rogers and L. Wisland, "Solar Power on the Rise," Union of Concerned Scientists, August 2014.
[7] N. Rahman, "Conservation At Its Best: The Passivhaus," Physics 240, Stanford University, Spring 2013.
[8] L. Thompson, "Green Building Standards," Physics 240, Stanford University, Fall 2010.
[9] B. Carey, "Construction Begins for Stanford's Student-Designed Solar House," Stanford Report, 28 Mar 13.
