It has been clear for some time that energy codes are on course to require carbon-free buildings by 2030. Adoption at the local level will see some areas of the country getting there even sooner. For example, California has set net zero goals for its residential code by 2020. These developments have accelerated the debate about the effectiveness of energy modeling versus performance-based approaches to compliance.
Let’s start with energy modeling, where change is coming for the better. In the past, the energy modeling community has been required to continuously respond to energy code cycle updates with new baseline models. That is, the bar for uncovering savings would be increased each and every time a new energy code was adopted. Following a code update, program staff and the energy modeling community would have to go through another learning curve to determine where to set a new bar and how to model the changes.
The stable baseline concept first introduced as Addendum bm to ASHRAE Standard 90.1-2013 fixes the baseline and calls for a differential performance for a proposed building. New energy code adopted, no problem. Same baseline, just increase the differential.
The benefits of this approach are myriad. To paraphrase a very thorough and informative Pacific Northwest National Laboratory (PNNL) paper on this subject:
- Same baseline and modeling rules can be used for both minimum code compliance and beyond code programs. The differential performance required is simply adjusted based on the purpose.
- Multiple uses for the same simulation ruleset make it more attractive for software developers to create reliable modeling tools with automated baselines.
- Consistent rulesets should increase the ability of building modeling professionals to produce consistent and comparable results that are much more reliable, less prone to gaming, and more likely to be acceptable to building officials.
Whether using a prescriptive approach or modeling for energy code compliance, these pathways are considered unreliable predictors of performance post-occupancy. Unfortunate but true, energy modeling can only take us so far. Despite our efforts, we cannot capture future building operations practices or simply put, how much of a priority energy efficiency will be for future owners, managers and operators. As they say, you can lead a horse to water….
Many have then argued for energy codes to go a step further– requiring performance thresholds. While this is not the current direction of the model code IECC and ASHRAE 90.1 Standard, which form the basis of state and municipal energy codes, post-occupancy targets are starting to gain momentum. The challenges here are significant. For one, how do we identify appropriate targets? And two, what are the rules for enforcement and what are the consequences for non-compliance?
The advantage of a performance or outcome based code is that it could extend to all buildings, not just new construction. Enter New York City, which has introduced a number of City Council bills to address both design and performance:
- Stretch Code. Building upon the NY State Energy Code, the Stretch Code will require new and major alterations designed and constructed as low energy intensity buildings beginning in 2025. Without getting into the weeds, this would essentially mandate Passive House level construction for both commercial and residential buildings, and would also enable a subset of these buildings to approach net zero with the use of renewables.
- Building Energy Grades. Starting in 2018, all buildings subject to NYC’s Benchmarking Law (buildings ≥ 25,000 sf) will be required to post their energy efficiency letter Grade A-F (based on Energy Star® source EUI – Energy Use Intensity measured in kBtu/SF). In addition, the bill will also require an “Energy Asset Score” to be disclosed at the time of sale or lease.
- On-site Fossil Fuel & Whole Building Energy Limits. Limits for on-site fossil fuel and whole building energy use will be applied to the subset of buildings subject to the NYC Benchmarking Law. Limits will be defined based on building type. Penalties for non-compliance would be implemented in 2030.
If NYC’s proposed regulations are any model, it seems as though we are on a collision course with an outcome based code. These regulations will likely spur new innovations in how we approach the design, construction, and operation of buildings. The new construction industry, including architects, engineers, contractors, and sub-consultants, will have to be more aware of the performance of their existing buildings. The next 10 years should be an interesting ride. Buckle up.
Written by Ryan Merkin, Director, Multifamily Energy Services