The Power and Peril of Reaching for Net Zero Energy in Affordable Multifamily Developments

Katie Ackerly, AIA, LEED AP, CPHC
August 2021
Simple diagram of a building.

Does achieving “zero net energy” for affordable housing matter? Or do we learn more about our real goals along the way?

Until very recently, zero-net energy projects have been flagship commercial, institutional or small residential projects. They are proofs of concept for a new era of building that sits lightly on the planet and contributes to a new, 100% renewable distributed grid infrastructure.

In 2019, many of us tried to process the reality laid out in the 2018 IPCC report: Humanity has until 2030 to not only change our habits, but to have changed our habits to avoid 1.5°C global temperature change and turn emissions downward. At the conferences I attended that year, I heard a distinct shift in tone from one-off demonstrations to scale: “We’re out of the pilot phase.” Awesome. And also, uh-oh: the pencils were supposed to go down before many people had even picked them up.

Then the last two years brought into vivid focus our collective vulnerability: near-constant weather events with unprecedented ferocity, and a global pandemic that laid bare the pervasive injustices of our society and links between these injustices to ecological collapse.

Coliseum Place

Entitled in 2015 and finally finishing up this year, Coliseum Place has been with us through these shifts in awareness around sustainable building. In 2016, we studied the feasibility of making this six-story, 59-unit affordable housing project a Living Building. In 2019, we committed to an ambitious goal to achieve a net zero energy design for an affordable housing project with developer Resources for Community Development (RCD). To skip to the end, the project will not be ZNE. Coliseum Place will have a 38% solar offset, which will cover all common loads, leaving the building to be virtually zero emissions—assuming residents maintain the 100% renewable energy offerings of the local community choice utility provider, East Bay Community Energy.

Set to be completed in October, Coliseum Place is predicted to tie for the lowest energy use intensity of any building in our portfolio, primarily due to the elimination of central hot water distribution. But it will not earn the sought-after designation that has inspired owners to take sustainability to the next level.

Being a sustainable design leader immersed in multifamily housing brings me face-to-face with the question: What happens when ambitious goals like ZNE meet a more conventional building industry that is structured on repetition and minimized first cost, especially one that struggles to keep up with massive demand?

Putting “zero” goals in context

As an essential construction type, housing interfaces with climate change mitigation in multiple dimensions. Housing defines how people live in relation to work, commerce, and society; it determines residents’ access; it can predict general health, welfare, and resilience of entire communities. Because of the many intersections of housing and climate change response, it isn’t easy for any specific sustainable design framework to accurately define what “good” looks like for urban housing. The chaos of a tight construction market further complicates the situation, challenging even the most resolute priorities.

That’s why the holy grail of “zero net energy affordable housing” poses a real dilemma: it presents a very clear and compelling goal with an understood value. But at the same time, such a narrow focus can limit recognition of other design opportunities—ones that may be equally impactful and come at little or no cost—and leave a wake of uncertainty should the ZNE goal fall apart. This is a problem for housing. When you leave opportunities on the table, you may be making climate change problems harder to solve while you’re trying to solve them.

The most obvious problem with ZNE affordable housing is density. A strict “on-site” definition of ZNE runs counter to the goal of denser residential construction, which reduces transit emissions and displacement by adding more stories and building more compact units. Although taller buildings have less room for solar panels (PV), height tends to drive energy use intensity down (assuming a similar wall R-value and unit mix). Energy use intensity (EUI) is the total amount of energy used over a year, per square foot of building. Meanwhile, denser buildings can add 5 points to the predicted gross EUI of a building because there are more refrigerators and televisions per square foot in more compact units. This spread is shown in new, detailed modeling results (see below chart) from the National Renewable Energy Laboratory in support of the ASHRAE Advanced Energy Design Guide.

Energy Use Intensity (EUI) for multifamily

Setting “zero energy” as a goal for housing doesn’t inherently provide feedback about how aggressively to pursue energy efficiency or where best to put limited resources. And until the ASHRAE design guide referenced above (the release of which has been delayed due to COVID), there has been very little effort to define a “lowest attainable” gross EUI for a dense, urban multifamily building.

In 2020, I worked on an advisory group to provide feedback on the ASHRAE guide, which offers target EUIs by climate zone for multifamily buildings, and allows any apartment building to call itself “zero-energy-ready” simply by meeting the target EUI (before PV application). In reality, the modeling yields a range of EUIs based on factors like height and density. But, as the guide explains, it offers one target representing a “high limit,” giving developers plenty of flexibility. For buildings in our climate (DOE climate zone 3C), the target EUI is 21. Comparatively, this is about a 50% reduction from a typical 2030 Challenge (“zero-tool”) baseline.

The predicted EUI for Coliseum Place is 17 kbtu/sf-year, which falls to 9 kbtu/sf-year with on-site PV. However, we will hold our applause until we collect actual utility data. In general, the few recently-completed buildings for which we have data use 20-50% more energy than predicted. Some of this can be attributed to inaccurate initial modeling combined with the use of cheap, natural gas to fuel hot water systems. But I would estimate that there is a significant disparity also due to the lack of testing verification and commissioning.

Edwina Benner Plaza, our first all-electric building, which was also designed to be zero-energy ready (predicted EUI of 15), is proudly operating very close to its prediction and below the ZNE-Ready threshold at 16.7 kbtu/sf-year. This success is most likely owed to a special focus on monitoring and optimizing the building’s energy use, making sure its super-efficient heat pump hot water system worked perfectly.

For Coliseum Place, we made a special point to advocate and carve out scope for blower door testing, quality insulation inspection and hot water pipe insulation inspection, which are elective points under GreenPoint Rated certification. The systems at Coliseum Place will also be tested by a third-party in spite of their simplicity, and building operators will receive a training on the rather unusual hot water system.

It is important to remember that for conventional multifamily housing development, it is still the little innovations—primarily in process, not product—that offer the most powerful emissions reduction opportunities. This is why, for me, pursuing ZNE housing is not so much about new technologies and solar energy as it is about driving a change in our standard decision-making process.

Five ways we can think differently

#1 Set a clear goal. The first step of a successful ZNE design process is committing to a clear goal, making sure it’s the right goal, and that it’s backed up by a hard commitment. Unfortunately, funding and municipal green building requirements do not tend to be based on EUI targets. Energy metrics are usually based either on a California Title 24 compliance margin or PV offset, neither of which prioritize the right efficiency measures. The goal should include a target EUI and as much PV as the owner can possibly afford, but the goal should also set the groundwork for these next steps.

#2 Evaluate value with cost. The second step is to use design processes and tools that allow the team to evaluate design options on the basis of value—a measure’s ability to enhance the quality of the project—rather than cost and compliance tools by themselves. For example, whole-building, predictive energy modeling, comfort, and life-cycle cost information should out-weigh energy code compliance modeling as a decision tool.

#3 Tie value to social equity. How the team defines “value” should be based on an examination of residents’ improved access to opportunity and be mindful of the complicated relationship between social equity and to technological innovation.

Coliseum Place taught us that energy efficiency was actually the least important selection criterion for residential heating, cooling and ventilation systems. Because HVAC system options are limited and bring enormous cost implications, resident health, comfort, resilience and sense of dignity and control, must take precedence. The good news is that you usually don’t have to trade efficiency for human benefits. But the attitude and approach matter. This logic should extend to all areas of design if we recognize all the ways in which the design of our homes and neighborhoods impacts our quality of life. The more that residents have to cope with a home that is isolating, unhealthy, or unsafe—or that becomes unsafe in a disruptive event—the harder it will be to reduce the overall, long-term footprint of housing.

To successfully reduce emissions in the multifamily sector, we should strive to give people of all incomes and abilities equal and fair access to technologies that allow them to adapt and thrive in a changing world. The COVID pandemic has thrown this imbalance of access into high relief. It also highlights a relatively cheap measure that might seem way outside the scope of a ZNE discussion: high-speed internet and virtual mobility. Many low-income households lack access to this essential service, which, pandemic or not, limits the community’s ability to thrive. Buildings can’t solve systemic inequities, but this represents the kind of blindspot we can have when global, greenhouse gas reduction goals define how we think about sustainable housing.

#4 Remember carbon. It’s important to remember that ZNE buildings can have very different carbon reduction profiles because ZNE buildings still use grid electricity, even though they contribute to an overall greener grid. Strategies to load shift and add storage can not only deepen emissions reduction, but also save the owner utility costs and contribute to community resilience.

Embodied emissions, which compete for more of our attention as our carbon-neutral deadline looms closer, is another factor. Coliseum Place taught us that, while we might assume there is not much room to reduce embodied emissions in a typical multifamily building, we can’t forget to have a conversation about our options. For a wood-framed building with one level of concrete, our structural engineer, KPFF, revealed that meeting achievable cement replacement levels would save about 175 metric tons of CO2e, which happened to be the very same reduction our ZNE measures would achieve by 2030, based on a crude, back-of-the-envelope estimation.

#5 Commit to verification. The last and most important change to our process is not new, but puzzlingly new to this sector: verification. This would include basic but thorough examinations of things like envelope framing efficiency, insulation installation and air tightness, efficient hot water distribution, and systems commissioning. The cost of the actual inspection and testing is minor within the context of large systems decisions, and setting the tone influences everything from more effective pre-construction meetings to successful hand-offs with building operators.

If Coliseum Place meets its ambitious EUI goals, it will be because the unconventional, distributed hot water system works optimally, which relies on the building manager’s understanding and compliance with the design intent.

We have many immediate changes to make and more to strive for in the coming years. To reach our goals—to have already changed our habits—by 2030, we have to act now. Part of that climate-responsive design always goes beyond meeting any singular, absolute goal like zero net energy. This is because most building types—most notably housing, perhaps—have inherent value to both climate change mitigation and adaptation, along with challenges peculiar to the building use that should cause a design team to shift priorities to reap the most benefit from investments. Finding the right set of strategies for each project is key to building a more resilient future.

Katie Ackerly, AIA, CPHC, is Principal and Sustainable Design Director at David Baker Architects, an award-winning firm known for elevating the design of multifamily housing. Katie came to architecture from a background in building science and energy efficiency policy, and holds a Master of Architecture and a Master degree in Building Science from UC Berkeley.