The Problem With Net zero
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Transcript of The Problem With Net zero
The Problem with Net-Zero Buildings (and the Case for Net-Zero Neighbourhoods)
By Nadav Malin
SERA is working with Portland State University as one of five pilot Eco Districts designated by the
Portland Sustainability Institute in a program aimed at removing institutional barriers to creating
sustainable neighborhoods. The team is looking at cogeneration, waste-to-energy, lots of heat exchange
among the energy strategies they’re hoping will help them get to net-zero.
Rendering: SERA Architects
Achieving a net-zero building with today’s technologies and occupant expectations is hard.
There are a handful of projects out there proving that it is possible—for the right building in the
right setting with the right team. But sometimes going after the goal of net-zero energy use in
the building can have unwanted side effects. For example, a low-rise building on a low-density
site will have a better chance of being net-zero with onsite renewables, but that type of
development is often known as “sprawl.” The investment in dollars and resources to get to net-
zero are significant and might be better spent on more cost-effective energy saving options,
such as a more efficient building envelope or creating a district energy system that can serve an
entire campus.
For all those reasons and more, some argue that while both have an important role to play, it’s
more useful and important to work toward net-zero energy communities rather than net-zero
buildings. Individual high-performing buildings don’t mean so much if the neighborhood as a
whole is wasteful, while if an entire community is net-zero, that’s meaningful even if the
individual buildings within it are not.
The Problem with Net-Zero Buildings
Net-zero energy is an ambitious goal for any building—one that can’t be achieved without
scrupulous attention to every aspect of a building’s design, construction, and operation. Like the
related goal of creating a carbon-neutral building, any net-zero building has to first achieve
significant load reductions and system efficiencies, and then meet the remaining loads with
onsite energy generation.
In some ways, net-zero is a tougher goal than carbon-neutral: By most definitions, a project
could become carbon-neutral using biofuels from off-site—that’s not as widely recognized a
solution for achieving net-zero. On the other hand, carbon calculations often account for the
energy and carbon expended to create a building—its embodied carbon—which is not usually
the case with net-zero energy.
Not every building can get there
Limits to Net-Zero for Multi-Story Buildings
Source: B. Griffith et al., “Assessment of the Technical Potential for Achieving Net-Zero-Energy
Buildings in the Commercial Sector,” NREL/TP-550-41957
Most buildings that generate their own energy do it with solar photovoltaics (PV). If we assume
that a building has only its roof area available for mounting PV, then a single-story building is
much more likely to achieve net-zero than a high-rise.
A 2007 report from the National Renewable Energy Lab (NREL) and the U.S. Department of
Energy (DOE) analyzes the potential for buildings in the U.S. to achieve net-zero energy using
energy technologies—both for energy efficiency and PV—that they expect will be widely
available in 2025. The graph below shows how their predictions play out based on the number
of stories. Getting to net-zero is extremely difficult for buildings of more than four stories. If the
project includes energy-intensive data centers, labs, or other spaces, the challenge gets tougher.
Other impacts ignored—or worse
Even if cost is not an obstacle and the building has a low profile, getting to net-zero means that
the solar panels can’t be shaded by trees or adjacent structures. That means that sprawling
suburban homes are much more likely to achieve the net-zero goal than dense urban
townhouses or apartments, and suburban office parks have a leg up on central business
districts. This is a problem we’ve seen before, according to architect Muscoe Martin, AIA, of
M2Architects: “In the ’80s a few solar architecture pioneers like Doug Kelbaugh and Peter
Calthorpe noted that most of the highest–performing solar buildings were in rural or suburban
locations, ignoring transportation and infrastructure energy use.” Martin notes, “Single-scale
problem-solving leads to solutions that don’t always make sense.”
The King Abdullah University of Science & Technology (KAUST) is a new 5.3 million
ft2 (500,000 m2) campus in Saudi Arabia designed by a team led by HOK. The $20 million
dollars spent covering the roof in roughly 400,000 ft2 (37,000 m2) of PV and solar thermal
provides about 7.8% of the total campus energy use. That’s not nearly as cost-effective as the
free 3%–4% overall energy savings achieved by changing the chiller utilization controls, notes
HOK’s Colin Rolfing. Controls also help campus-wide. The Inter-Campus Automation System
(ICAS) helps take advantage of the diversity of energy loads by sending excess electricity, chilled
water, and steam from the solar panels and from the central utility plant to buildings that need
it the most.
Transportation isn’t the only impact that is often (but not always) ignored when focusing on the
building. The energy and environmental costs of supplying potable water and treating
wastewater, providing energy and data infrastructure, and creating roads and transportation
systems are all beyond the scope of most buildings, yet necessary to support their functions. The
Living Building Challenge, created by the Cascadia Green Building Council and now managed by
the International Living Future Institute, is the rare exception that accounts for these impacts by
stipulating zero municipal water consumption and wastewater discharge, and requiring that all
buildings be located on previously developed sites.
Version 2 of the Living Building Challenge, released in 2009, goes even further in this broader
focus by requiring a focus on design for “car-free living.” It also anticipates the importance of
reaching beyond the individual building with the concept of “scale jumping,” which allows
project teams to link buildings together to achieve the requirements as a group.
Opportunities with Communities
Neighborhoods and communities, being larger than individual buildings, can support many
technologies for low-impact heating, cooling, and electricity generation better and more cost-
effectively. To some extent, this is simply a matter of scale: combined heat and power systems—
especially those using biomass—are more efficient in larger sizes. Perhaps more important,
they can support dedicated operations and maintenance staff to keep them working properly.
The same is true for community-sized boilers, chillers, and many other high-tech solutions.
Many colleges and universities already have centralized energy infrastructure, as well as an
entire community under common ownership, making them natural candidates for becoming
net-zero. “University campuses are going to be the early adopters in this game,” says Eric
Ridenour of SERA Architects in Portland, Oregon, citing long-term ownership of their buildings
and access to patient capital (as opposed to investment funds seeking a quick return).
One example of a community-scale cooling system that would not have been feasible for an
individual building is Cornell University’s deep-water cooling system in Ithaca, New York, using
water from Cayuga Lake to replace three existing chiller plants. Reaching two miles out and 250
feet into the lake for cold water, this system cost about $60 million, some of which would have
been spent anyway replacing chillers and CFC refrigerants. It saves about 25 million kWh
annually, reducing Cornell’s total electricity bill by 10 percent.
More cost-effective energy generation
Cost-Effectiveness of Community-Scale Renewables
Source: “Economic Investigation of Community-Scale Versus Building Scale Net-Zero-Energy,” S.
Katipamula et al., December 2009. U.S. DOE report #PNNL-19095.
In a report published in 2009, Srinivas Katipamula and others at Pacific Northwest National Lab
(PNNL) compared five different scenarios for achieving net-zero energy use for a mixed-use
community of about 16,000 people. They assumed that all buildings in the community would be,
on average, 70% more efficient than typical U.S. buildings. They then compared the cost of each
of the following options for both Chicago and Phoenix:
• PV on each building;
• PV in an adjacent solar farm;
• concentrating solar thermal electricity;
• wind turbines on leased land;
• and wind turbines on purchased land.
They were surprised to find that, on a cost-per-kWh basis, wind on leased land was the winner
even in Phoenix, which has abundant sunlight and a relatively poor wind resource. PV on
individual buildings was the second-to-last choice in both cities, beating only solar thermal
electricity in Chicago, and wind on purchased land in Phoenix (see graph).
Load diversification and cascading uses of energy
Communities also have a mix of occupancies and uses, which can support more efficient use of
infrastructure and cascading uses of energy. Offices use most of their energy by day and can go
dark at night, while for residences it’s just the opposite. That means that a single heating or
cooling plant serving both can be not much bigger than a plant serving just one of them. It is also
sometimes possible to share energy—using waste heat from data centers, for example, to heat
water for use in apartments. Looking into the benefits of this diversification for neighborhoods
in Portland, Oregon and Seattle, the architecture firm Mithun found the ideal mix of residential
to commercial uses to be 75% to 25%, according to president Bert Gregory, FAIA.
Mithun and engineering firm Arup are now designing new mixed-use facilities for a state office
campus in Baltimore, Maryland, and exploring potential synergies. One discovery they made is
that they can get many of the benefits of a central heating and cooling plant with equipment
distributed in the basements of several buildings by linking the equipment together into a
“virtual central plant.” That solution gives them the benefit of modular equipment, so each
device can come online as needed and operate at optimum capacity. More important, it solved a
phasing problem by removing the need to invest in a large central plant before all the demand
was in place.
Criterion Planners of Portland, Oregon, has estimated that a full 25% of the building energy
savings in a prototype LEED for Neighborhood Development community can come from district
systems, including both plant efficiency and peak load diversity. Another 10%, in their model,
comes from the increased density.
A more inclusive scope
In Freiburg, Germany, the Vauban district is recognized internationally for its efforts to
discourage car ownership and promote alternative transportation. This 5,000-person
community, built on a former French army base abandoned in 1992, also has highly efficient
buildings. Over 100 are built to the Passivhaus standard, and the “Solar Settlement”
neighborhood boasts 59 “Plus Energy” houses, designed by architect Rolf Disch, that generate
more energy than they use. Most of the community’s remaining energy needs are supplied by a
biomass-fired cogeneration system.
Photo: Tom Brehm
A net-zero-energy community is not simply a collection of buildings that, taken together,
achieve the goal of net-zero-energy. A community includes loads and energy uses that are not
often included in the equation for individual buildings, such as wastewater treatment and other
community infrastructure, not to mention designing to support low-impact transportation
options. These represent opportunities for environmental gain that extend well beyond energy
efficiency, including water conservation, rainwater infiltration to reduce runoff, the social
benefit of reduced car dependence, and even urban agriculture for a local food economy.
All of these infrastructure and planning-scale issues directly or indirectly involve energy use:
wastewater and stormwater treatment have energy costs for the city; transportation and
transporting food both require fuel for vehicles. They are also tied into quality-of-life issues that
are best addressed at the neighborhood scale—by creating spaces that make dense, urban living
appealing, for example.
The Irvine, California, consulting firm CTG Energetics has created a sophisticated community-
impacts calculator that aggregates data from a range of sources, including energy models of
typical buildings in the community, transportation models, and water-related energy use, to
quantify the impacts of community design choices. By addressing infrastructure in addition to
individual buildings, and resources beyond energy, it gives project teams a framework for
considering tradeoffs and avoiding the pitfall of too narrow a goal.
Better control of orientation and massing
For an individual building project, site constraints and preexisting street grids may make it
impossible to orient the building for optimal daylighting and passive solar heating or cooling.
“As much as 50% of the heating and cooling energy can be saved by going from the worst
orientation to the best orientation, and street layout has a tremendous impact on the
orientation of buildings,” said Norbert Lechner, architect and professor emeritus at Auburn
University.
When designing at the community scale, those considerations can be addressed in ways that
help make the individual buildings more efficient at minimal cost. The best example of this is
Village Homes in Davis, California, where all 200 houses are on east-west streets even though
the parcel of land is mostly north-south, according to Lechner. “Not only does every house save
energy by receiving mostly winter sun and little summer sun but the cooling systems are also
smaller and less expensive,” he said. Village Homes was built in the 1970s with a focus on solar
design of individual homes and innovative stormwater management, but it doesn’t appeal to
transportation-minded planners today, who see it as yet another example of a car-dependent,
suburban neighborhood.
Challenges at the Community Scale
Despite all the advantages, there are many reasons why community-scale approaches are not
more common.
Ownership and financing
Large, developer-led, mixed-use projects such as Dockside Green in Victoria, British Columbia,
or London’s Beddington Zero-Energy Development (BedZED) consolidate the ownership and
management into one entity, so that they can coordinate design, construction, and management
of an integrated project. There is even greater potential in revitalizing existing urban
neighborhoods, but doing that introduces many new challenges.
Mithun has explored several projects that could become urban ecodistricts, linking together
many different buildings and uses, owned by separate entities, into a coordinated network. In
the process, they’ve discovered a range of challenges. Who owns the infrastructure that’s
needed to share utilities? How do you create governance structures that encourage private
investment while coordinating it in a way that optimizes community-scale design? How do you
get permission to connect buildings across public streets? And what do you do about utility
regulations that make it difficult to create small, neighborhood-scale utility companies? Without
a single owner to be accountable and responsible for these systems, all kinds of legal and
commercial problems emerge.
Phasing
Net-Zero Energy Buildings and Communities: Advantages at each scale
Most large, mixed-use projects are created in phases rather than all at once. That makes it hard
to invest early in efficient, centralized infrastructure such as HVAC systems, transportation
networks, and ecological wastewater solutions. But if those systems are not in place early on,
then individual buildings and units have to build separate systems to meet those needs, creating
obstacles to doing centralized systems later. Financing those investments before there is a
critical mass of occupants to use them is a key challenge for many large projects.
Overly complicated technologies
The more sophisticated systems that are possible in a community-scale project require
dedicated management, so there has to be an organizational infrastructure in place to support
the physical infrastructure. This problem gets even worse for communities that are pursuing the
goal of net-zero energy, because they tend to seek out the most advanced technologies available
rather than the tried and true. At BedZED, the combined heat and power system using biomass
never worked as advertised and was replaced by gas boilers after a couple of difficult years for
residents, who endured winters with limited heating. The onsite wastewater treatment system
also failed repeatedly.
Overreaching for unreliable technologies is one problem, but any large, mixed-use project lends
itself to complicated systems and potentially unwieldy design and construction, warns Mithun’s
Sandy Mendler, AIA. “Added size sometimes creates complexity that pushes against the
efficiencies of scale, and there is an extra coordination effort when a large team is involved.”
That complexity gets even worse when there are multiple owners and regulatory agencies
involved.
Letting buildings off the hook
The National Renewable Energy Lab’s new 220,000 ft2 (20,400 m2) Research Support Facility is
designed to be net-zero, with predicted energy use of 32 kBtu/ft2 (3 kBtu/m2)—to be offset
with PVs on the building and in the parking lot.
Courtesy of: DOE/NREL, Photo: RNL Design
Clark Brockman, AIA, of SERA, acknowledges that net-zero individual buildings may not be the
right goal: “I don’t believe that we’re ever going to get to a time when all the buildings are net-
zero,” he says. But he does believe that every designer should have the experience of creating a
net-zero building, because until they’ve done that they won’t understand what it means to
design to absolute, physical limits. “It will change the way you work,” Brockman says.
Any model for net-zero communities assumes that the buildings themselves, while not
necessarily net-zero, are extremely energy efficient. A risk of focusing on the community is that
the efficiency of individual buildings will get short shrift. This fear is corroborated by
conversations Mendler has heard among the team working at the University of California’s new
green campus in Merced, suggesting that they needn’t push the efficiency of individual building
envelopes as much because the central plant is so efficient. This dynamic can occur any time a
centralized solution is perceived to “solve the problem” for the project.
Losing touch with the inhabitants
Every net-zero-energy project depends on the full participation of its occupants to get that way.
“In the case of individual buildings, the onus is on the owner or occupants to balance
consumption with generation,” notes University of Florida’s Charles Kibert, Ph.D. “I don’t see
this as achievable at larger scale because we are back to the ‘commons’ again—there is no
vested interest for all the individual recipients of energy to limit their consumption,” he adds.
The Oregon Sustainability Center, intended to serve as a hub and incubator for sustainable
enterprises near Portland State University, is seeking Living Building certification. The design
was scaled back from 230,000 ft2 to 200,000 ft2 (21,000 m2 to 18,500 m2) based on feedback
that it could not achieve net-zero at the intended size. It has since evolved further, to 150,000
ft2 (14,000 m2).
Graphic: SERA Architects/GBD Architects
The project team for the Oregon Sustainability Center—a 200,000 ft2 (18,600 m2) multi-tenant
project pursuing Living Building certification in Portland, discovered just how critical the
occupants would be when they broke out the energy loads in their net-zero-energy model and
found that occupant loads accounted for a full 50% of the energy use. “That changed the whole
game,” says Brockman. “Now we have an entire section of our energy model that is devoted to
occupant behavior,” he adds, noting that in addition to predicting usage schedules and
thermostat set points more precisely, they also have to codify those assumptions for the tenant
guidelines.
Brockman isn’t daunted by the need to expand that level of occupant engagement to the
community scale, however. He envisions a “fractal dashboard” model, with outputs at various
scales displaying actual performance in real time at different levels of detail, from the
community all the way down to the individual occupant. Net-zero communities won’t be
achieved without effectively driving down energy use in each individual building—it’s just that
not every build ing will get to net-zero.
What’s the Right Scale?
“The right scale is the scale that you have before you,” says Muscoe Martin, arguing that it’s
better to do what you can within the scope you’re given than to do nothing at all. At the same
time, he notes, it’s useful to think in terms of “nested scales” and consider the impact of your
project on the products and systems within it, and on the systems in which it fits. Every project
should help make its neighborhood more pedestrian-friendly, for example, even if it can’t
redesign the entire streetscape.
Net-zero is a compelling goal, both for individual buildings and for communities. Like any
generic goal, however, it has to be applied wisely. “There is no question that you have to focus
on every individual building because you want to drive down the loads as much as possible,”
says Malcolm Lewis, president of CTG Energetics. “The trap is thinking that you have to make
each building completely self-sufficient, because in doing that you sacrifice opportunities.” Some
buildings won’t get there—so how do you set equally compelling targets that those buildings
can achieve? Other buildings might get there, but with unfortunate side effects, such as
increasing car-dependence. In those cases it’s important to expand the scope of the challenge to
include transportation impacts and other community level impacts, and optimize the design
based on a wider view of the goal.
It’s not all about technology and design, however. No matter how cleverly they are built, we
won’t have net-zero buildings or communities unless we change the way that we live and work
in them. That’s a challenge that we’re all facing together.