Net Zero Energy Building
As with many other businesses, advancements in technology have enhanced construction methods and performance. Our knowledge and excitement continue to increase as we learn more about efficient and sustainable construction products and applications. Here at AFT Construction, we have been fortunate to have built some amazing projects over the past several years and have been able to incorporate many of these technological advances in terms of building techniques, materials, and of course smart home products. While we have implementing certain elements in previous and current projects, the next opportunity that we are very excited about is constructing a net zero energy building.
What exactly is a net zero energy building?
There have been varying definitions used and there are certain reasons for that such as a lack of an industry standard definition and what the goals are the project are. At its core, a net zero energy building is one that produces at least as much (renewable) energy as it consumes on an annual basis. In other words, it must produce one unit of energy for each unit of energy it consumes over the course of a year. It is a building that is designed to be very energy efficient to reduce the required energy with the balance of the energy needs supplied by on-site renewable energy technologies. In fact, this is essentially the definition set forth by the World Green Building Council, which defines a net zero carbon building as “a building that is highly energy efficient and fully powered from on-site and/or off-site renewable energy sources.” (https://www.worldgbc.org/advancing-net-zero/what-net-zero)
The Department of Energy and its National Renewable Energy Laboratory (NREL) has defined a zero-energy building as “an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.” (https://www.energy.gov/sites/prod/files/2015/09/f26/bto_common_definition_zero_energy_buildings_093015.pdf)
Notice the Department of Energy definition uses source energy as its basis rather than simply the energy consumed. Source energy basis not only takes into account the actual energy used on-site by the building, but also the energy it takes to produce and distribute the energy to the building site as well as energy losses that may occur along the way. Using this basis will generally mean the building will need to produce and export more renewable energy to achieve net zero status.
Another concept contained in the Department of Energy’s definition to highlight is energy consumption versus exported energy. The reason to highlight this concept is to point out that net zero energy buildings are generally connected to the energy grid using traditional energy sources such as electric and natural gas in the same way any other building is connected to the energy grid. The purpose of staying connected to the traditional grid is there may be times when the energy loads (requirements) of the net zero energy building may be greater than the on-site production is able to supply. In these times, the traditional grid will supplement the required energy needs. However, there will be times when the on-site energy production is greater than the building’s loads and the excess energy will be exported back to energy grid. This excess production can offset later energy usage. Note, the Department of Energy defines exported energy as “on-site renewable energy supplied through the site boundary and used outside the site boundary.” (https://www.energy.gov/sites/prod/files/2015/09/f26/bto_common_definition_zero_energy_buildings_093015.pdf)
Technologies and Strategies to Construct a Net Zero Energy Building
Now that we have a basic understanding of what a net zero energy building is, the question becomes what technologies and strategies are required to achieve net zero status. This post is intended to only highlight and summarize these technologies and strategies.
At the heart of any net zero energy building, the technologies used for energy production will most likely be solar photovoltaics (solar panels) and, when appropriate, wind turbines. Additionally, more specific applications such as solar water heating can be incorporated.
However, energy production is only part of the equation of achieving net zero status. Just as important is building an extremely energy efficient building to reduce the overall use of energy. Not surprisingly, achieving net zero status starts early in the planning and design stages. The important concept to remember is to make design decisions that will further achieve the net zero energy goals. For purposes of this discussion, we will assume the building being constructed is a residential home.
One of the first steps in building an energy efficient home is to properly orient the building on the site. This means maximizing north and south exposure while minimizing east and west exposure. Proper orientation is extremely important in hot climates such as we have here in Arizona.
After proper orientation, other design concepts to incorporate include daylighting and natural ventilation. The concept of daylighting revolves around the controlled admission of natural light and direct sunlight into the home to help reduce electrical lighting. The basic idea is that proper design will allow sufficient natural light into the home to reduce and even eliminate the need for electrical lighting during certain times of day. The balance here is to let as much natural light in as possible while minimizing the amount of direct sunlight coming into the home as too much direct sunlight can lead to increased cooling costs. Ways to combat excessive solar heat from entering in the home is through the use of window technologies that reject heat such as low-e glazing or products such as windows films. Overhangs can also be installed to protect windows and exterior doors.
That concept of natural ventilation centers on ways to naturally remove heat and cool the inside of the home. Examples of this include intentionally placing windows in places that take advantage of natural wind patterns in order to get a cross breeze through the home. This allows the occupants to feel cooler without the need for air conditioning.
There are other materials and ways to naturally or passively cool the home. Reflective barriers such as choosing a light paint color, which reflects most heat is a better choice versus dark paint colors that can absorb 70-90% of radiant energy. Incorporating shading through trees, drapes, and blinds can help reduce heat entering into the home. Like the natural ventilation, ceiling fans can help rooms feel cooler for the occupants reducing the need for air conditioning. A couple other ideas include installing roof vents to ventilate hot air from the attic and the use of radiant barriers on the underside of the roof to reflect heat.
In terms of making the home more energy efficient requiring less energy usage, there are some building materials that we have used in current and past projects that are very effective. Advanced framing, a system designed for more spacing between studs to allow for more insulation, is a valuable building technique. Proper insulation is key to not just keeping the heat out in the summer, but also keeping the house warm in the cooler months. Utilizing spray foam versus tradition fiberglass insulation will make a home more energy efficient because it provides superior insulation, seals air leaks, and can be sprayed into places that are hard to reach with fiberglass insulation. Closed foam can be used in certain locations for additional structural strength. Another product for superior insulation comes in the form of insulated concrete foam (ICF) walls. ICF walls are double insulated, steel reinforced concrete walls that make up the exterior walls of the structure. Due to the expanded polystyrene foam sheets on both sides of the reinforced concrete, ICF walls provide two layers of insulation, which results in a high R-value and low air infiltration rate (reduced air leakage). Additionally, the insulation provided by ICF walls is generally more consistent than with traditional wood framing, which can reduce or eliminate cold or hot spots. All of this leads to a much more energy efficient home, which is key to achieving net zero status. We also use structural insulated panels (SIPs), which are insulated panels used for truss systems, floor systems, and even walls.
Lastly, it is important to incorporate energy efficient products into your home to reduce and minimize energy loads. These include items such as LED light bulbs, energy efficient appliances, properly sized HVAC systems, etc. The more energy these energy efficient products the save, the less exported energy the site will need to produce.
The good news is that building a net zero energy home is becoming more and more cost effective. The most important thing to remember is to go into the build with a solid plan from the very beginning, which requires making decisions that will further the net zero goal. By following these strategies, a net zero energy home can be a reality.