- energy benchmarking and goal setting
- passive design features/climate responsive design
- energy modeling
- onsite renewables (solar, wind)
- Net Zero Energy/Net Zero Carbon Building
How much energy does the project use? Is any of that energy generated on-site from renewable sources, and what is the net carbon impact? The burning of fossil fuels to provide energy for buildings is a major component of global greenhouse gas emissions, driving climate change. Sustainable design conserves energy while improving building performance, function, comfort, and enjoyment. How did analysis of local climate inform the design challenges and opportunities? Describe any energy challenges associated with the building type, intensity of use, or hours of operation, and how the design responds to these challenges. Describe energy-efficient design intent, including passive design strategies and active systems and technologies. How are these strategies evident in the design, not just the systems?
This particular topic is vast, and particularly difficult for generalists to master. The resources in the Toolkit focus on the purview of the architect. For example, although passive measures are usually the sole responsibility of the architect, impacts to other systems such as lighting and HVAC design will likely follow. Very-high-performing buildings will require some knowledge of all the resources in this measure, particularly by the design team leader and project manager. To close the loop on predicted energy use versus actual energy use, link Design for Energy with Design for Discovery.
High-performance buildings have been a central focus in the COTE® lexicon since its inception. What is different now? With advanced technologies, new tools, and workflows, the architect has an increased ability and responsibility to plan for high performance.
Energy benchmarking and goal-setting
- This is a critical first step for every project. For a simple building, this process can be done in an hour, and is easily accessible to an architect. A more complicated building type or more advanced analysis can take a day or more, but can yield greater insights into energy end uses, costs, and unique loads on the building.
- The Resources section below highlights several tools to help build a robust benchmark for most building types.
- Benchmarks are easily shared with the design team and owner, and are a basis for a deeper conversation about how the building is intended to work. Everyone on the team should understand a project’s benchmark and its energy goals.
- Lighting Power Density (LPD) is measured in watts per square foot (W/sf) of installed lighting. This is a great indicator of a project’s energy performance. Projects with a lower LPD will use less energy. Set a goal for LPD of 25–50 percent better than code. Check the LPD often throughout the design process.
- Windows are a major indicator of total building energy use. A Window-to-Wall Ratio (WWR) above 40 percent will provide no additional benefit for daylighting but will cause significantly higher conditioning loads. Keeping the WWR between 30 percent and 40 percent will set the stage for both good daylighting and energy performance. (Limiting the WWR may feel like a design restriction for project teams; however, the way designers leverage constraints to their advantage is one of the key considerations of the AIA COTE® Top Ten Awards, celebrating both beauty and performance.)
- Very efficient buildings tend to have a great percentage of the energy coming from plug loads. Like LPD, it is important to set a goal for plug loads and check them throughout the design process. Determine the typical plug load (in W/sf) for buildings with a similar program, and aim for a 25 percent to 50 percent reduction. Scheduling nonessential plug loads to turn off when not in use can be a primary strategy for reaching 50 percent reduction.
Passive design features/climate responsive design
- Indigenous and native typologies offer great clues for climate-responsive design. Prior to the advent of air conditioning and other modern technologies, materiality, massing, orientation, roof design, and penetrations were the strategies used to build comfortable and protective enclosures. Use vernacular and indigenous buildings as a guide to determine the passive strategies that are most applicable for a given region.
- Focus on WWR, orientation of glazing, and sun shading as major passive strategies. WWR should be limited in all climates, but the location of glazing will shift depending on the latitude. In colder climates, primary glazing should be on the south, to collect beneficial solar radiation. In warmer climates, primary glazing should be on the north, to avoid harsh summer sun. For the most part, windows should be shaded on the south, east, and west in all climates.
- Envelope air tightness is just as important as insulation but often receives less attention. To ensure good air tightness, designate one layer of the assembly as the air barrier and ensure that this layer in continuous on six sides, with all seams taped, and all penetrations filled. Use a blower door test to verify the building's air tightness, both for mockups and for the whole building.
- Provide operable windows for all occupants so that the building can benefit from fresh outdoor air when the weather is agreeable. Arguments have been made that non-operable windows provide better control for building systems and save energy. This can be true only if the building knows more about each occupant’s thermal comfort than the occupant does. This is not the case; always provide operable windows.
- AIA’s 2030 Commitment clearly demonstrates the relationship between energy modeling and high performance. When an energy model is performed, higher performance is a typical outcome. While energy modeling is very specialized, there are clear roles for the architect in the process.
- Build iterative energy modeling into your project’s design budget. Whether the work is done in-house, in cooperation with a utility program, or working with a consultant, there are many ways to integrate analytics that inform the design into your project.
- Energy modeling can be done to varying degrees of detail and scale. An energy model done early in the project might be rough and include many assumptions, versus a more detailed model later in the design process. It is also a good idea to think about energy modeling related to specific assemblies. For example, thermal bridging can be modeled, and the envelope design can be tested and fine-tuned.
- Consider the energy model as a cost-control measure, not as an add-on for sustainability. Energy is relatively easy to quantify and predict (as opposed to savings from daylighting), and the report can be used to manage first costs (system size), operational costs (utility bills) as well as other Non-Energy-Benefits (NEBs).
- If the scope of the project is too small for an energy model, manage the WWR and LPD. These simple calculations are excellent proxies for energy modeling.
- Much of a building’s energy use is tied to the building’s function. A hospital can be incredibly energy-intensive with a baseline average Energy Use Intensity (EUI) of 280, whereas an office might have an EUI around 90. Look closely at occupancy schedules, occupant densities, operational hours, and physical form. How do these variables affect what measures are employed?
Onsite renewables (solar, wind)
- An in-depth study by the National Renewable Energy Laboratory shows a 60 percent decrease in the cost of commercial photovoltaic (PV) systems over the period from 2010 to 20171. PV costs continue to fall; renewables are now less expensive than some common energy-efficiency measures. Due to the frequency of change and the number of variables, seek an up-to-date professional quote to accurately assess cost.
- Coordinate the system sizing and area of your array with NREL’s PV Watts tool.
- While large-scale on-site wind production can provide a significant amount of power to the building, it is appropriate only in certain conditions (usually very rural locations with uninterrupted wind sources).
- Building-mounted wind turbines have not performed well in tests to date. Also, solar thermal systems are not appropriate for most building types. The focus for on-site renewables should be on solar PV.
- Design all buildings to accept solar PV and hot-water arrays in the future. This includes increasing roof load capacities, maintaining large clear areas on the roof or site to mount panels with no obstructions, selecting the correct meters, leaving room for inverters, and providing additional capacity for electrical panels.
Net Zero Energy/Net Zero Carbon Building
- Several definitions exist for Net Zero Energy Buildings; for the sake of simplicity, we define it here as a building that creates as much energy as it uses through renewable sources (typically PV or wind) over the course of a year. For a Net Zero Carbon Building, the building must offset as much operational carbon as it uses over the course of a year. This can include some mix of on-site renewables and off-site Renewable Energy Credits (RECs).
- A challenging goal for any building, NZC may nevertheless be a more accessible target for some projects. Project type, shape, size, and access to adequate renewable energy sources all factor heavily into a building’s ability to meet this goal.
- A building is not considered to be NZE until after at least a year of operations it can be verified that it performs at this extremely high level. Third-party verification or certification is highly recommended.
- Prioritize energy efficiency and the use of on-site renewables over the use of RECs. RECs play a key role in a resilient and decentralized power grid made up of primarily renewable energy sources. However, it is far more impactful to minimize the energy used on-site than to draw clean energy from a distant source. Consider achieving NZC with no more than 20 percent RECs.
- Consider a Power Purchase Agreement (PPA), with which a portion of the building or site is leased to a third party for on-site renewable energy. The owner receives the benefits of a low carbon energy source without substantial first costs of the renewable systems.
- A higher priority should be placed on RECs that are local to the project.
- RECs must be third-party–verified so that they cannot be sold more than once on the open market.
- An “operation carbon calculation” isolates the carbon emitted during the life of a building, as opposed to an “embodied carbon assessment” that would include the carbon entrained in the materials.
- Eliminate carbon downstream of the meter by designing all-electric buildings.
- Building Commissioning (Cx) is incredibly important for ensuring that the owner is getting the building for which they paid. Cx can be expensive but tends to pay back quickly and provides valuable quality assurance/quality control. Scope can vary greatly and should be carefully coordinated with the systems being proposed in design.
- Retro-commissioning should be recommended to the owners to assess systems performance after the first three to five years of operation.
- Fu, R., Feldman, D., Margolis, R., Woodhouse, M., & Ardani, K. (2017). U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017. National Renewable Energy Laboratory. Retrieved from https://www.nrel.gov/docs/fy17osti/68925.pdf