EUI and Custom Homes
Energy Use Intensity (EUI): This is a mathematical figure that is calculated by dividing the energy usage of a building over the course of a year by the building's square footage. Why does this number matter? By measuring energy expenditure we can understand the efficiency of a building and it’s environmental impact. Think of EUI for a building as Miles Per Gallon (MPG) for a combustion engine car.
EUI is measured by taking the energy input for a building, which in the United States is measured in kBTU, and dividing that number by the square footage of the building. We can convert that number to an average over a year to best understand the building’s performance. Energy use is first an estimated number during the design stage. Later is can be measured to a more exact number once a building has been used for its intended purpose for a year.
For custom homes, at the design stage we are looking at the amount of energy consumed as predicted at the building site by energy modeling software. We take the 3D model that we use for design and construction documents, and we run an analysis that takes into account the thermal performance of materials, the type of mechanical system, the efficiency of the glazing, the amount of inhabitants, the use of electricity, the amount of passive lighting and heat gain and the heating and cooling degree days to predict what the EUI may be for that house. Once we know the prediction, we can adjust the design to meet our energy reduction goal.
A common energy reduction goal is the 2030 challenge. The 2030 challenge is part of the Paris Climate Agreement, and sets the goal of creating carbon neutral buildings by the year 2030 of which operate on renewable energy sources without greenhouse gas emissions. There are milestones along the way that building professionals aim to meet to ensure they are on track for the 2030 challenge: 80% reduction in energy consumption as compared to the average building performance in the project’s region by 2020, 90% reduction in energy consumption as compared to the average building performance in the project’s region by 2025, and finally, the carbon neutral goal by 2030.
-At beginning of design you can determine a baseline and try to meet that target. Think of this first step as setting the goal. A resource for understanding what the current baseline is, and determining an EUI reduction target is the Zero Tool.
-Use passive design strategies to create low or no cost solutions for building operation. Different strategies vary depending on different climates, but can include earthen homes, or partially sinking the home into the ground to regulate temperature. Using intentional passive lighting strategies like light shelves, skylights, solar tubes and the appropriate ceiling and window height for the room depth, using vegetation for shading, and water features for evaporative cooling.
-Use energy efficient technologies and building systems. Some examples are occupancy sensors for electricity control, energy efficient heating and cooling systems, geothermal heating and cooling and heat recovery ventilators for fresh air.
-On or off site renewable energy to account for the building demands. Most sites can benefit from photovoltaic panels as a flexible and cost effective solution to generating renewable energy. Other sites may be able to utilize wind turbines.
-Continual EUI modeling to analyze the building design as the design progresses.
Energy efficient technologies and sustainable materials usually come with a price as compared to traditional building materials and equipment. For this reason, designing for the lowest EUI possible is not for every client. Most often, we are seeing a few measures making it into the project, but there often is not the budget to include all of the options available to us. We foresee the cost barrier vs. demand as being a continual challenge in the near term and encourage any level of EUI reduction that the client is open to using.
