Developing buildings that generate as much energy as they use during the course of a year has become an important goal for the most environmentally minded owners and architects over the past decade or so, and a growing number of projects are succeeding in meeting this ambitious target. For some building types, however, meeting net-zero requirements can be particularly difficult. So taking shape is a new, bigger-picture approach that considers this concept at a community or district level.
With scale comes savings
No matter how efficiently designed, high rises with limited roof space and energy-intensive hospitals (to name two examples) can find it impossible to meet annual energy needs through on-site generation. In addition, researchers and developers looking for new ways to make net zero more affordable are discovering that spreading capital costs across multiple buildings and maximizing economies of scale can make energy targets more affordable and, possibly, add resilience to facility operations.
“Any time you can put in bigger systems, spread across several buildings, there are economies of scale on a whole range of systems,” said Shanti Pless, a manager with the Commercial Buildings Research Group at the National Renewable Energy Laboratories (NREL).
Pless cites load diversity—buildings with different use patterns that can benefit from sharing resources—as an advantage.
“On the mechanical side, up to 30 percent less cooling tonnage can be required across a larger group of buildings, versus individual buildings,” he said.
Victor Olgyay, a principal with Rocky Mountain Institute (RMI), said some more specifics to the diversity a mixed-use development could have in its loads.
“Restaurants often have large loads—warehouses, not so much,” he said. “Some buildings are used during the day, others at night. When you put this mix together, you get a much better chance of getting the overall development to balance out to a zero-energy district.”
Optimizing a multibuilding development for net-zero performance begins early in the planning stages, especially if new buildings are part of the effort. Site planning, for example, can be critical to a project’s future success in meeting energy goals, according to Olgyay.
“When beginning at a larger scale, lots of site goals can be coordinated, and often, passive or bioclimatic approaches can be designed in,” he said.
For example, buildings can be positioned to foster cool breezes or create sunny garden areas. Also, how buildings are massed—whether tall and slender or long and low-slung—can affect on-site energy production.
“On a recent project, we increased solar electricity production by 25 percent, simply by arranging the building massing for optimal solar access to solar panels,” Olgyay said. “Of course, this planning can reduce energy use by providing access to daylighting of buildings, as well.”
Building an energy budget
As with individual buildings, getting to net zero on a district basis begins with maximizing efficiency of all buildings within the boundaries and understanding how much generation capacity is available on-site. Massing issues can complicate this process because each tweak in building orientation can affect everything from solar heat gain and daylighting availability to solar exposure for photovoltaic panels. Energy-modeling software capable of considering all of these variables is an important tool for designers during this process.
“One of the big concerns at a district scale is about ensuring that we are designing to a realistic energy and financial budget,” Olgyay said. “If a site has a certified capacity for generating electricity, we use that to determine the energy-use intensity of the planned development. The idea is that the solar electricity generation capacity modeling, energy-load modeling and financial modeling all inform each other.”
NREL has taken a role in bringing what is now a maturing building-level modeling-software industry into district-level projects. There are several issues to deal with, from building massing to where a solar array might be placed.
“As a national lab, we’re looking at what’s happening next,” Pless said. “The really interesting opportunity is interfacing that modeling process with utility distribution-system loads; there are a lot of opportunities for a district system to support a more efficient utility distribution system. That’s the next front in these integrated modeling tools.”
NREL is exploring district-wide modeling in two Denver projects that are in the planning stages. The National Western Center is a reimagining of the city’s National Western Stockshow Complex, a 130-acre site that is home to the annual National Western Stockshow. Planned to grow to 250 acres, the new center is intended to add nine new buildings and operate as an agricultural education extension of Colorado State University.
The second NREL project, the Sun Valley EcoDistrict, will involve a redevelopment of a low-income neighborhood dominated by the subsidized Sun Valley Homes housing project, along with a variety of light-industrial and warehouse buildings. Also, the community is home to a legacy district steam power plant, which could prove helpful to developers, plus a new light-rail station will give the anticipated 3,000 residents new emissions-free transit options.
Pless said NREL’s involvement in these two local developments is a win-win situation for both NREL and developers.
“Because they’re trying to do things that have never been done before, they’re going to come up against barriers,” he said. “By partnering with these local projects, we get a sense of those barriers.”
Free energy for life
At a much larger scale, the New York City-based consulting firm Terrapin Bright Green, co-founded by longtime energy efficiency and environmental advocate Bill Browning, is aiding the master planning of a Florida community that could include up to 170,000 homes. Browning started his career helping with Buckminster Fuller’s last experimental structure and went on to found the Green Development Services at RMI and serve on the founding board of the U.S. Green Building Council. He has long been at the cutting edge of high-performance building design and development.
The Florida project is intended to be built as a series of neighborhoods over several decades, with each neighborhood featuring its own ground-mounted solar array. In addition to freeing roof space for possible solar hot water installations, a centralized, neighborhood-wide array offers economic advantages.
“The whole question of mounting arrays is a lot simpler if you’ve got one large array [rather than a large number of individual, home-mounted units],” he said. “It gives you economies of scale.”
The idea to make the community net zero came out of market research focused on seniors looking for retirement homes. Prospective buyers were polled on whether they would prefer free golf (golf courses are a part of the plan) or free energy for life.
“Eighty-five percent of the respondents said free energy,” Browning said. “Particularly if you’re on a fixed income and you don’t know where energy costs are going to go—that can be a little scary at times.”
Solar is the dominant energy resource for the community, so storage is part of the plan. However, this won’t just mean stationary batteries in basements; it also could mean a vehicle-to-grid approach drawing on electric golf carts while they are connected to charging equipment.
Keeping plug loads in check
One of the big issues with stand-alone net-zero buildings is ensuring consumption doesn’t creep upward over time. Building occupants, not lighting or heating and air conditioning systems, are generally the biggest culprits in this situation, as they begin overspending the energy budget on coffeemakers, desk lights, electronics and other miscellaneous plug loads. Maintaining planned performance is an even more important consideration across an entire district.
Pless said addressing occupant use goes back to the basic foundation of net-zero design, which is building and renovating structures to be as efficient as possible, with high insulation levels and high-performing heating, ventilating and air conditioning systems. If more is invested in the simple passive stuff, the less one will have to depend on occupant use patterns.
“If you’ve already got the load down, and it’s already pretty efficient, on aggregate, that’s maybe another advantage of looking across a district—you’re less dependent on users operating the building poorly,” he said.
RMI has worked to develop market-based concepts that provide financial incentives for both owners and tenants to meet efficiency targets in net zero and other high-performing developments. Such contractual agreements can help companies and individuals internalize the benefits of efficiency.
“For example, in a typical incentive-aligned, or ‘green,’ lease, the savings that accrue from energy savings are shared between the tenant and the landlord,” Olgyay said. “The same can be extended to include energy generation, where producers of electricity benefit from selling their excess to others.”
Browning is a fan of providing occupants with real-time consumption status in an easy-to-understand format instead of the running kilowatt-hour displays on a typical utility meter. He cites a net-zero apartment complex designed for agricultural workers and their families in Woodland, Calif. Each of the 62 units in the Mutual Housing at Spring Lake development features a color-coded energy monitor indicating whether the occupants’ energy use is efficient (green), typical (yellow) or above normal (red). Those who stay within the units’ normal range pay only a $5 monthly energy administration fee, while those who exceed the estimate pay added charges.
Bright future for broader approach
While district net-zero planning is still at the pilot-initiative stage, the advantages of spreading costs and load-diversity across multiple buildings make the approach likely to become more common. Olgyay said his organization sees a strong future for such designs going forward—and business opportunities for electrical contractors who involve themselves in these projects.
“At RMI, we believe creating more successful net-zero districts will result in feasible strategies for quickly increasing the amount of variable renewables on the grid, with financial and grid-stability benefits for the utility and the consumer,” he said. “This is an emerging area where the market for electrical contracting can really shine.”