Let’s Talk Net Zero: Preparing for Evolving Code

BUILDING DIALOGUE: It’s All About the Carbon

ASHRAE and IECC are headed toward creating net-zero energy standards for commercial buildings by 2030. California will have zero net energy building codes in place by 2030. It will not be too long before other states and cities adopt these standards as code. Boulder (Climate Mobilization Action Plan) and Denver (80×50 Climate Action Plan) already have set goals that all new buildings achieve net zero energy by 2031 and 2035, respectively.

Mohit Mehta, LEED AP BD+C
Principal/Building Performance Director, ME Engineers

If you are considering a net-zero project, you will want to be aware of the various definitions of net zero energy and how projects should go about achieving it.

• What is a net-zero energy building? There are many definitions of net-zero energy floating around our industry developed by world-renowned organizations like the U.S. Department of Energy, and national laboratories like the National Renewable Energy Laboratory. Simply put, a zero-energy building, also known as a zero net energy building, or a net-zero energy building, is a building with zero net energy consumption, meaning the total amount of energy (electricity, gas, chilled water, steam, etc.) used by the building on an annual basis is equal to the amount of renewable energy generated on-site.

The International Living Future Institute’s Zero Energy Building certification requires 100% of the building’s energy needs on a net annual basis be supplied by on-site renewable energy without the use of on-site combustion (i.e., all-electric buildings).

Architecture 2030 (goals adopted by the American Institute of Architects) allows purchasing approved offsite renewable energy and/or renewable energy credits but only up to 20% of a building’s remaining energy use to meet their definition of a carbon-neutral building – a building that uses no fossil fuel, greenhouse-gas-emitting energy to operate. This definition makes it possible for more buildings to achieve ZNE, even with poor solar access or other site and roof area constraints.

We do not know what final definition the cities of Denver or Boulder will end up with as part of their net-zero energy codes as conversation among experts and advocates have introduced alternative terminologies like net-zero carbon and net-zero emissions codes.

Relationship between EUI reduction and increase in onsite renewable energy. Source: Jamy
Bacchus (ME Engineers).

These are currently under consideration. There is no shortage of articles, guides, books and organizations dedicated to net-zero buildings if one is interested, and regardless of which definition we’d like to adopt for our project, achieving ZNE comes down to implementing two steps (in addition to hiring an A/E team that has the expertise, creativity and commitment needed to achieve zero energy goals):

1. EUI reduction or minimization.

2. Offsets using renewable energy:
a. On-site predominantly; and
b. Off-site secondarily (no more than 20% per AIA’s 2030 Commitment Program).

EUI stands for energy use intensity expressed in kBtu per square foot per year. It is the energy use per sf at a property (energy divided by sf). EUI enables us to compare different sized buildings. Other common terminologies to keep in mind:

• Site energy use– the annual amount of all the energy your property consumes on-site, as reported on your utility bills.

• Source energy use– a more accurate representation of a building’s energy footprint as it considers the site energy as well as the energy lost during production, transmission and delivery to the site.

Nevertheless, a low EUI is needed to achieve ZNE. With that said, there are some building types that set up better for ZNE than others. For example, in Colorado the most energy-intensive (high EUI) building types are restaurants, health care facilities, hotels and data centers, where achieving ZNE will be challenging (not impossible) since there may be not enough roof area available to offset the energy the building uses. ZNE likelihood also is limited by the building’s height and the number of floors in the building that some urban sites might demand. ZNE is easier to achieve on warehouses (not refrigerated), offices (excluding high-rise), retail buildings and schools.

• Whole-building energy modeling is a critical first step to achieve ZNE. Whole-building energy modeling (BEM) is a versatile, multipurpose tool that is used in new building and retrofit design, code compliance, green certification, qualification for tax credits and utility incentives, and real-time building control. By “energy modeling,” we mean using computer-based tools to simulate the energy use of a building throughout an entire year of operation. This also is commonly referred to as annual energy use simulation or building performance simulation.

We use the energy model to calculate a building’s pEUI (predicted EUI) – the only reliable way to do so. For this we need to have knowledge of the building’s real-world operation (i.e., how will it be used).

Understanding how a building uses energy allows us to target the areas that have the most impact to get the maximum bang for the buck. For example, not every building type will benefit from exceeding code-required envelope insulation values – one of the first things we consider when thinking “high-performance.” This helps us direct the project’s resources wisely to the areas that move the needle.

Steps to Approach Net Zero

To achieve NZE, we suggest the following order of operations:

1. Reduce energy demand through aggressive load reduction.

2. Use free energy resources and passive engineering.

3. Use the most efficient technology possible.

4. Recover waste energy.

5. Incorporate renewable resources/energy (on- and off-site).

In our experience, success is achieved only if each step is exhausted before moving to the next step.

Strategies for EUI Minimization

There are many pathways to achieve a ZNE building with more becoming available as new technologies are developed, as existing technologies improve, and as renewable energy technologies rapidly advance. Here is a list of areas and strategies that projects pursuing ZNE will need to address and optimize to be successful within the framework of the five steps listed above: climate analysis; building massing; window-to-wall ratio; solar controls and passive solar design; building envelope and infiltration; user behavior, educating and engaging building occupants; daylighting and lighting; equipment, receptacle schedules and loads; HVAC and service water heating systems; and renewable energy systems.

Conclusion

Each project will forge its own path to achieve ZNE. We have seen average projects achieve ZNE because the project was able to fund a large enough on-site solar PV array to offset all its energy use, while several high-performance and even ultra-low energy projects not reach ZNE status because they did not have that extra capital to fund on-site renewables or did not have the roof or the site area available.

ZNE may be a concept and a choice today but it will be baseline building energy code for new construction sooner than later in Colorado, especially with signing into law the recent House Bill 19-1261 – Climate Action Plan to Reduce Pollution. This law sets the state on a path to reduce 90% of statewide greenhouse gas emissions by 2050.

With that said, there are numerous tangible and intangible benefits of ZNE buildings. Total cost of ownership is potentially lower. These buildings are thoughtfully designed and constructed and are better insulated with tighter envelopes that lead to quieter, more thermally comfortable spaces and have longer lifespans with increased durability. They maximize the use of daylighting thus connecting the occupants to the outside/nature.

Key Takeaways

To recap, the central takeaways from the first column in the series were:

1. Atmospheric CO2levels are rising year after year and corresponding to warmer global surface temperatures.

2. The building industry is the leading cause of CO2emissions.

3. Merely designing to energy code compliance and green building certifications such as LEED are not enough; thus, state and local governments have committed to adopting net zero building energy codes and source 100% fossil fuel-free energy.

And from this column:

1. Energy codes in Colorado and especially cities along the Front Range are moving toward developing ZNE building codes.

2. Begin every project with a whole-building energy model to assess pEUI and energy by end-use (how and where the building uses energy).

3. Exhaust all measures and strategies to reduce your project’s EUI.

4. Consider renewable energy offsets: on-site plus approved offsite options.

Published in the December 2019 issue of Building Dialogue.