Set performance goals for the project
After you have performed a benchmark analysis, there are several approaches that can be taken to set performance goals for the project. Regardless of the goal-setting approach, it is important to set the goals as early as possible in the design process such that there is a measuring stick against which to track progress.
Meet or exceed code baseline performance
All projects must comply with the local energy code, so the base level of performance must meet the code requirements. Be sure you understand the modeling rules as they may vary depending on the project's location.
While code compliance is mandatory, many projects will set a performance goal that exceeds (i.e. performs better than) the code requirements. These types of goals are often expressed in terms of "percent better than" the code. Projects that set this type of goal are often motivated to do so by a specific program. For example, beyond-code programs such as green building rating systems, or utility incentive programs often award credit (in the case of green building programs) or monetary incentives (utility incentives) based on energy modeling analysis that demonstrates that the proposed design performs better than the energy code baseline by a specific percentage.
While this is a fairly common target-setting approach, it must be noted that, because the energy codes are updated on a regular basis, this type of target becomes less meaningful over time. As an example, if a project was designed to exceed the 2010 energy code by 10%, but the code was updated in 2013, 2016, and 2019, then how does the building perform compared to the 2019 code? In order to get the answer, a new energy model would need to be created to compare the design against the 2019 baseline.
Energy Use Intensity (EUI) is one of the more common metrics used for benchmarking building performance, so it is becoming common for projects to also set performance goals based on EUI. Some programs such as the AIA 2030 Commitment call for participants to submit EUI values for their projects on an annual basis and therefore, architects will often set an EUI target early in the design process in order to design towards that performance. As noted in the benchmarking page, EUI may be expressed in terms of site and source energy, so be sure to understand the difference.
EUI has become a commonly used metric because it allows for the potential for modeled performance (during the design stage) to be compared against measured performance (during the operational phases of the building). However, there are some notable challenges associated with this comparison. During the design phase, there are many unknown variables about how the building will be operated such as (but not limited to): hours of operation, quantity and magnitude of plug loads, number of occupants in the building, and many operational factors related to the building systems. Additionally, building use may change over time (for example, a tenant that works long hours may replace a tenant that used the space 9:00 to 5:00, or a space may add large server equipment). While best efforts may be made to estimate these operational features during design, the operational (measured) EUI is likely to differ compared to the predicted EUI during design.
Zero Net Energy (ZNE) performance
Zero energy buildings combine energy efficiency and renewable energy generation to consume only as much energy as can be produced onsite through renewable resources over a specified time period. Achieving zero energy is an ambitious yet increasingly achievable goal that is gaining momentum across geographic regions and markets. Private commercial property owners have a growing interest in developing zero energy buildings to meet their corporate goals, and in response to regulatory mandates, federal government agencies and many state and local governments are beginning to move toward zero energy building targets.
Zero energy buildings may be defined by different metrics (e.g. zero net site energy is different than zero net source energy).
A useful set of resources for determining strategies to achieve zero net energy performance for specific building types are the Advanced Energy Design Guides. DOE notes that : "This series of guides, created through an industry partnership [between U.S. DOE,] ASHRAE and other market leaders, provides user-friendly guidance for achieving a zero energy performance in various building types. They include sets of energy performance targets for all climate zones. Strategies on how to achieve these energy targets are provided throughout and include setting measurable goals, hiring design teams committed to that goal, using energy simulation throughout the design and construction process, and being aware of how process decisions affect energy usage. The intended audience of this guide includes architects, design engineers, energy modelers, contractors, facility managers, building operations staff and facilities planning staff."
Carbon emissions targets
Some projects use carbon emissions as a metric for setting performance targets as opposed to energy consumption. Interestingly, this may result in choosing different design strategies than buildings that are only focused on site energy reductions. For example, installing on-site batteries may help to store energy (generated by PV systems, or drawn from the grid) during periods where the grid is operating with lower GHG emissions (e.g. during mid day when PV generation accounts for a greater proportion of production). This battery-stored energy can then be used by the building during peak grid periods (e.g. in the evening when PV production reduces and fossil fuel "peaker plants" come back online). While this battery storage/discharge doesn't actually save energy (in fact, the storage/discharge actually results in a slight increase in energy consumption), it does effectively shift the loads and reduce reliance on the grid during periods when the grid is producing higher levels of GHG.. Projects that seek to reduce GHG emissions tend to look for both strategies that reduce energy consumption, and shift demand on the grid to periods when the grid is operating with low GHG emissions.
In addition to operational carbon emissions, some projects also seek to offset embodied carbon - carbon emissions that are the result of the manufacture of building construction products, and emissions associated with the construction process itself. For buildings that wish to offset carbon, the process would be to:
- Model the building to determine its annual operational carbon emissions
- Calculate the embodied carbon of the building
- Design a PV system that can offset all of the annual operational carbon emissions and embodied carbon (embodied carbon would likely be offset over time by oversizing the PV system such that it is essentially net-negative carbon each year and eventually the embodied carbon would be offset by that annual surplus).
As a final note, while this section largely deals with "carbon" emissions, there are many other greenhouse gases (GHGs) that must be accounted for. These additional GHGs are often accounted for using a metric called CO2e (equivalent carbon emissions). CO2e accounts for the global warming potential (GWP) of carbon and other GHGs such as methane, nitrous dioxide, and others by consolidating their GWP into a single metric.
Energy cost targets
While many of the other targets noted above are focused on reducing energy consumption or environmental impacts associated with energy consumption, another target may be based on financial considerations. A project may set a target to reduce energy cost compared to the code baseline, or it may aim to perform such that the predicted utility bills are less than a target cost. These analyses are performed by producing an annual whole-building energy model, then using the utility rate structure to calculate predicted energy costs. As noted above in the discussion on EUI targets, many assumptions about operational factors during the design phase could cause these energy cost predictions to differ from the actual energy costs once the building is operational.
- Zero Energy Performance Targets for New Construction Buildings - New Buildings Institute has released a paper that details energy use intensity (EUI) recommendations for zero energy new construction projects across all U.S. climate zones and for common building types.
- Advanced Energy Design Guides - ASHRAE resources for determining strategies to achieve zero net energy performance for specific building types.
- Embodied Carbon in Construction Calculator (EC3) - A calculation tool that gives builders and designers information about the embodied carbon impact of building materials during the material selection process.
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