Have you heard the term ‘net zero energy building’ and wondered what it means? If so, you are not alone. Its definition can vary significantly depending on which country you are in and with whom you are speaking.
At one end of the spectrum, a net zero site energy building is one that collects the same amount of energy on site as it uses from energy utilities over a year. One step up from this is a net zero source energy building, which collects the same amount of energy on site that is consumed at the source to generate the required energy delivered. Not exactly a subtle difference. According to the EPA, between 2001 and 2005 only about 30% of power plant energy consumed made it to the end user due to power plant inefficiencies and distribution losses.
Further, a net zero emissions energy building is one that generates enough energy on site to save an equal amount of carbon emissions produced by the utility for the energy required. While this sounds similar to the previous definition, some take this to include emissions from construction, transportation, and manufacturing, referred to as a building’s total embodied energy. There are also net zero energy building definitions that involve purchasing renewable energy only and truly off-the-grid building that uses no energy utility whatsoever. Even with off-the-grid building, there is debate regarding embodied energy, sanitary discharge, and water supply, which also require energy for treatment and distribution but are often forgotten in the conversation. Composting toilets and grey or rainwater harvesting are tools available to help reach total independence. Generally, U.S. net zero energy building commonly implies net zero site energy building, while Europeans focus more on embodied energy and emissions.
“No matter the exact definition, all net zero energy buildings utilize, and often epitomize, the same design tools applied in green building, particularly integrated design.”
No matter the exact definition, all net zero energy buildings utilize, and often epitomize, the same design tools applied in green building, particularly integrated design. The central goals behind net zero energy building are first to restrict, then to reduce, and finally to replace the energy needed. To avoid and restrict initial demand, a mix of both ancient and hi-tech tools exists. From Pueblo to Viking to Sumerian, ancient cultures had to use natural means for protection from the elements. Today, we have returned to many of their techniques – passive solar, thermal mass, natural ventilation, and selective daylighting – to provide some of the most cost effective and low maintenance tools in achieving energy neutrality. Aside from providing shelter, these climate-specific methods can also engage us with our environment. Hi-tech analytical tools like energy modeling, daylighting, and computational fluid dynamics software allow calculation of the impact of some of these ancient techniques. In addition, new high performance products, such as low emissivity glazing and adjustable, bioclimatic facades, are constantly being introduced and improved.
Reducing energy use simply involves efficiently addressing loads that cannot be restricted and therefore relates to systems like HVAC and lighting. Geothermal heat pumps, LED lights, Energy Star appliances, and condensing boilers are examples. Energy replacement entails the installation of systems that collect and store or share energy. These take the form of solar thermal, photovoltaic, and wind turbine systems, among others. While debate exists between energy conservation and harvesting, there is no doubt that restricting and reducing energy use limits the amount needing to be replaced.
The more holistic net zero energy definitions help explain how the perceived altruistic parts of green building standards, such as LEED, relate to energy neutrality. Through material selections accounting for embodied energy and neighborhood designs addressing travel and infrastructure, there will come a day when ‘energy plus’ buildings yield more than they demand, reverse and diversify the grid, and end the age of fossil fuel.
– Bryan C. Smith, PE, LEED AP
Bryan is a Licensed Mechanical Engineer, a LEED Accredited Professional, and Board Member of the USGBC Central Pennsylvania Chapter. Please feel free to contact Bryan for further details regarding the above information.