In the District of Columbia (District), the Building Energy Performance Standards (BEPS) take into consideration existing buildings performance but leave new construction requirements in the scope of DC Energy Conservation Code (DC ECC) . Since new construction buildings become existing buildings the moment they are occupied, it is critical to understand where the two policies overlap during design and construction to ensure compliance with both. To aid owners and designers in this endeavor, this resource:
- Addresses the central question of whether or not a DC ECC-complaint building will meet the thresholds for the first BEPS compliance cycle. Readers familiar with DC ECC can skip to that section.
- Analyzes how DC’s most recently constructed projects are faring for the first BEPS compliance cycle.
- Dissects the DC ECC for areas that will most likely have the greatest impact in BEPS compliance.
- Describes opportunities to make decisions in new construction and major renovations for long-term BEPS compliance.
“The 2017 DC Energy Conservation Code was finalized and took effect on May 29, 2020. As one piece in a new suite of codes, the DC ECC is the most applicable code section to help meet the BEPS standard.DC ECC
The DC Energy Conservation Code
Energy codes have long been the primary (and often only) means of regulating the energy performance of buildings. Energy codes regulate construction events—whether the construction of new buildings or alterations made to existing buildings—and set minimum requirements for the components of the building’s energy systems. As a consequence, energy codes regulate design and don’t regulate actual energy use.
Compliance paths and performance proxies
Within the DC ECC, there are three paths for demonstrating compliance: prescriptive, modeled performance, and alternative compliance. This resource focuses on analysis of the first two compliance pathways only and their proxy to determine actual energy use.
The prescriptive path establishes a set of specific requirements for the components of each of the energy systems, with minor variations based on building type and system type. As a result, compliance with the prescriptive path is fairly straightforward, but can also lead to widely different actual performance outcomes from one building to another. Some of the primary variables that lead to different outcomes include:
The prescriptive path sets a maximum window-to-wall ratio (WWR), and buildings with less WWR will perform very differently than buildings with higher WWRs.
The prescriptive path is not material neutral, so it has different requirements for different fenestration materials and different envelope assemblies. Actual outcomes can therefore vary based on which envelope materials are included in a design
Some HVAC system types are inherently more efficient than others, yet the prescriptive path considers them all equally code compliant. Actual energy outcomes can therefore vary based on which HVAC system is included in the design.
The commercial section of the energy code has the same base requirements for all non-residential buildings, even though larger and taller buildings may have much denser internal loads (from higher occupancy densities and the additional equipment that is required in taller buildings) than shorter buildings, which can have significant impact on the space conditioning energy use.
Other design decisions such as building massing, geometry, orientation and site exposure also impact energy performance but are largely unaddressed in code.
The result is that two buildings using the same energy code, following the same prescriptive path, can have widely different actual performance outcomes, making it clear that the requirements in the prescriptive path do not lead to a certain actual outcome, but serve as a proxy for a base level of performance.
Modeled performance path
The modeled performance compliance path relies on computer-based modeling to compare the energy performance of the proposed design to the energy performance of a code-defined reference design. The modeled performance path allows for considerably more flexibility—lesser performance in some building components can be traded off against greater performance in other building components. Even though modeling removes some of the variables that impact actual performance, it leaves others in place and even introduces new ones, listed below.
Modeled Performance Path
The modeling done for code compliance is not meant to provide a prediction of the building’s energy performance, but an evaluation of the building’s performance compared to code under a set of prescribed conditions.
Modeling methodologies contain simplifications of how energy moves and is consumed in a building. For example, most code compliance methodologies assume that heat transfer through envelope assemblies is parallel when it is actually three-dimensional. As a result, modeling methodologies typically underestimate the impact of thermal bridges, which can vary substantially among different envelope assemblies and different designs.
Modeling methodologies often allow simplifications of systems. For example, water heating distributions systems can be modeled with a simple heat loss factor for the distribution system and simplified schedules for when hot water will be flowing through the distribution system. This can under- or over-estimate the amount of heat that is moving from the hot water distribution system into the conditioned space, which can result in an inaccurate impact on space heating and cooling loads. And this impact will be much larger in some building types such as high-rise multifamily than in other types with much smaller hot water loads such as retail.
The building’s actual operational characteristics—schedule, temperature setpoints, occupant density, plug loads, etc.—could be different from those assumed in the model, even widely so, and may change over time.
The closer the project will be located to the weather station where the weather data was recorded, the more accurate the model will be
The quality and accuracy of the modeler can also lead to very different building performance.
Regulated and unregulated loads
Energy codes only have requirements for some of the loads in buildings. Some user-driven loads—particularly plug loads and process loads—are not entirely regulated by the energy code, leaving a significant portion of building energy consumption largely unregulated. Therefore, these unregulated loads, which would not be tracked for compliance with the DC ECC, would have a potentially significant impact to a building’s actual energy use.
Building Energy Performance Standards
Unlike building codes, the BEPS regulate actual building performance. A new building becomes an existing building as soon as it’s built, meaning that new construction will almost immediately need to measure real world performance—which is regulated under BEPS.
For newly constructed projects, taking on additional work shortly after the building is complete may be out of the question, so careful planning for both the compliance with the DC ECC and BEPS is required at design.
Will a 2017 DC Energy Code-complaint building meet the BEPS threshold?
The short answer is that it depends on building typology and whether short- or long-term compliance with BEPS is a goal of the project. Given that ENERGY STAR score is a mix of contributing factors around energy use, energy source, and occupancy density, the DC ECC will only benefit the energy use impact of the score. The operations and human density will need to be determined through lease agreements (offices) and design decisions (multifamily).
In 2017, PNNL completed an analysis of the DC ECC. The team at New Buildings Institute analyzed the results of that study as it relates to the BEPS regulation. A full description of their technical analysis and how conclusions were derived is available upon request.
It is highly likely that commercial office buildings built under the current code would meet the thresholds for the first BEPS period. However, it is not a guarantee, and it’s quite possible that an office building constructed to current code-minimum standards would only be compliant in the first cycle of BEPS, and may not be compliant long term as the standards ratchet up over time.
It is, unfortunately, more likely that multifamily housing built to current code minimums would not meet the BEPS threshold, even in the first cycle. The performance ranges are more varied depending on size of units and the unit mix in a building. These buildings would be considered compliant with DC ECC, but not necessarily with BEPS.
How DC’s recently-built projects are performing
Based on publicly disclosed benchmarking data, buildings constructed recently (from 2015–2017, which were first benchmarked in 2018–2019) are performing fairly well compared to the current the 2021 Building Energy Performance Standards.
Most of the office buildings reviewed will comply with the first cycle of BEPS, and even though it is presumed these buildings were built under the previous code (2013 DC ECC), many comply with the performance requirements of the 2017 DC ECC.
Of the multifamily housing buildings reviewed, almost 30% will not comply with the first cycle of BEPS. While the average ENERGY STAR score for these properties is above the standard, there is a wider range in scores.
For a full assessment of the buildings reviewed, contact us.
How the new code can aid in BEPS compliance?
The DC ECC provides opportunities for buildings to meet the BEPS thresholds through prescriptive options (with scores likely to range) and performance options. When pursuing the performance path, testing the energy model regularly by inputting results into Target Finder will help the design team know if they are on track to meet the BEPS.
In the prescriptive path, there are new areas that are going to help drive down building energy use, and options such as providing onsite solar generation that will help move a building’s ENERGY STAR score up:
- Solar (Chapter 13). This section gives designers two options: Provide 10 kBTU/sq. ft. of solar generation based on roof size, or provide 4 kBTU/sq. ft. combined with higher-efficiency mechanical systems and additional plug and process load requirements. Both options will help improve a building’s ENERGY STAR score. On-site solar will influence the source energy use portion of the score, and the higher-efficiency mechanical systems and lower plug loads will help to bring down the overall site energy use.
- HVAC Controls (Chapter 6). Captured in multiple sections of Chapter 6, HVAC controls give the owner and operator the ability to set back, ramp up, and turn off HVAC systems when they are not needed. Proper installation and calibration during commissioning will allow these systems to optimize the system to meet the building’s temperature and ventilation requirements at the same time as managing the energy consumption and peaks. These systems can also easily allow for regular recommissioning to ensure that set points and operating schedules are meeting the needs of the building owner and occupants.
- Plug and Process Loads (Chapter 8 and Chapter 10). Plug and process loads are playing an increasing role in the total energy use of a building (see Figure 1 above). By regulating even a small number of plug loads, significant energy reduction can be achieved. Chapter 8 requires automatic control of outlets in office spaces, while Chapter 10 requires the installation of ENERGY STAR equipment, which is shown to use less energy annually than its peers.
- Energy Type Metering (Chapter 8). Metering will most likely not save money or energy immediately, but by setting up metering by fuel type and end use (typically referred to as submetering), the building operators will have the information they need to monitor systems and fuel consumption to best optimize the building’s energy use and have easy access to data for continuous commissioning, retuning, or retro commissioning when numbers move outside of normal ranges.
- Commissioning (Chapter 11). Commissioning of the building systems will ensure they are set to operate at the most efficient levels.
Why building owners and practitioners should consider going above code minimums to aid in long-term BEPS compliance
For owners and designers to consider the long-term impacts of their design decisions, emphasis should be placed on reducing overall energy use, and decisions that will have long-term staying power. Often building envelopes last for the entire life of a building, while HVAC and water heating equipment will get changed out every 15–20 years. Providing better insulated wall assemblies helps to reduce internal loads for heating and cooling, which can also reduce the required HVAC system size. Using the façade design intentionally to aid in daylighting for interior spaces will reduce lighting loads when paired with daylight sensors (as required by DC ECC). Investing in the longest lasting systems with energy impact will provide the greatest return in long-term BEPS compliance.
The code is full of minimums, and achieving better values is often within reach of generic off the shelf equipment and ready-made solutions. Instead of specifying the minimum values for equipment and systems, look to go beyond the required minimums.
Is the building built only to code minimums sufficient for long-term compliance with BEPS? It appears that in some cases, the code will get you across the finish line for the first compliance cycle. Unknowns in future thresholds make longer term projections difficult, but careful design and decision making during the construction process using the 2017 DC ECC should produce a building that complies for the first few compliance cycles, if it is maintained and operated correctly. Building owners looking to invest in their construction for longer term compliance with BEPS should focus on envelope optimization and high-efficiency heating and cooling systems, paired with modern control systems that will allow them to carefully monitor systems and the need for intervention and upgrades going forward.