The Emergence of Zero Net Energy
Creative Thinking Needed for the Trend to Be Sustainable
According to the U.S. Department of Energy (DOE), commercial buildings, including offices, schools, hospitals, restaurants, hotels, and stores, consume nearly 20 percent of all energy used in the U.S. That translates into more than $200 billion spent each year to power millions of square feet of space that is often designed or operated inefficiently, according to DOE research, which results in 20 percent or more of that energy and money being wasted.
Given these statistics, it is no wonder building owners and operators are frequently investing in energy-saving solutions, such as improved lighting, occupancy sensors, and better building controls. But a growing number are going a step further and looking to design buildings that produce as much energy as they consume each year. These so-called zero-net-energy (ZNE) buildings may sound like a pipe dream, but they’ve already become a reality in many parts of the U.S. and around the world.
One of the groups behind the ZNE movement is the New Building Institute (NBI), Vancouver, Washington, a nonprofit organization whose mission is to advance commercial building energy efficiency. “Our focus on ZNE has been in the works for the last three to five years, and we published our first “Getting to Zero” report in 2012,” said Ralph DiNola, CEO, NBI. “Our most recent report, which was released in 2014, showed the ZNE trend is happening in more than 38 states, in every climate zone, and in a whole variety of building types, including private, public, new, and existing.”
In fact, that latest Getting to Zero update reported that since the first update was released in 2012, the number of ZNE buildings has increased by 52 percent, and projects on the path to ZNE have increased by 182 percent. Granted, the number of buildings either achieving or targeting ZNE performance is still quite small at 191 projects, but everyone needs to understand this is a growing trend, said DiNola.
“This is the next big wave of sustainability in the building sector, and we want people to understand they should be proactive about getting involved, because, otherwise, they’ll be left behind. And no one wants to play catch-up.”
ZNE construction will grow in the future, just as the NBI data shows, said Richard Hermans, director of training and advanced applications, Daikin Applied, even though the total market of new construction of ZNE buildings is still relatively small. “But, there have been enough private stakeholders who have included low-energy buildings into their business plans to move this from a fad to the familiar and perhaps soon to common practice. As equipment manufacturers react to the growing market for very high-efficiency products, more products like this will be developed.”
End users and early adopters driving the ZNE trend have found that first cost is higher in these buildings, but not prohibitively so, said Dru Crawley, fellow/director, building performance, Bentley Systems Inc.
“By radically reducing the loads, the required heating and cooling plant is much smaller, with a smaller first cost. Similar cost reductions throughout the building help to keep first costs down, and, unlike incremental change in energy efficiency, this can break through the cost barriers.”
Various states, utilities, and the federal government are also driving the trend toward ZNE buildings with California, for example, seeking ZNE building status for all new commercial construction by 2030. The federal government established the Energy Independence and Security Act of 2007, which set a goal of achieving ZNE building design and cost-effective construction in the U.S. President Barack Obama also recently signed an executive order that stated, beginning in 2020, all new construction of federal buildings greater than 5,000 square feet must be designed to achieve ZNE.
ZNE activity is accelerating, but it’s still in the initial phases, and the drivers vary from region to region, said Lisa Tryson, director of corporate communications, Danfoss. “Generally speaking, it started with public — particularly schools — and nonprofit buildings, but is now spreading to a much greater range of building types and ownerships, including developers seeking to sell high performance as a differentiator and government efforts to make federal buildings high-performance or energy-independent.”
Every Building is Unique
While there is no universal template that can be used with ZNE structures, many of these buildings share certain characteristics. The main goal in these types of buildings is to reduce the load, said Paul Torcellini, principal engineer, Commercial Buildings Research Group, National Renewable Energy Laboratory (NREL).
“You need a good, tight thermal envelope, and you want to be able to manage the solar gains. Next, lights add heat to the building, so use daylighting as much as possible and turn off the lights. Good insulation, good solar management, and reducing the lighting as much as possible will radically reduce the air conditioning load of the building.”
The HVAC systems used to handle these smaller loads may also differ, although the following characteristics are often found in the equipment selected for ZNE buildings, said Alan Niles, Western region commercial sales manager, WaterFurnace Intl. Inc.:
• Easy means of independently providing each zone with cooling and heating;
• The ability to capture all waste energy and economically transport that energy throughout the building to where it can be used or stored for future use;
• A scalable system that can be used on any size building without a drop in system efficiency;
• The ability to easily transport energy to and from non-HVAC systems like refrigeration cases, ice making machines, and domestic hot water; and
• The ability to easily connect to on-site renewable energy sources like solar, ground loops, and biomass.
Several energy design guides have advocated using water-loop heat pumps in ZNE buildings, as they can achieve all the criteria listed above, added Niles. “Water-loop heat pumps can connect to a building’s non-HVAC systems as well as to on-site renewable energy options in order to achieve as much of a ZNE design as a project’s budget will allow.”
Other types of HVAC equipment can also be used, said Hermans, who noted Daikin’s recent involvement in a ZNE office building resulted in the ventilation, domestic hot water, and space heating and cooling being supplied by heat pumps. “Smaller ZNE buildings may benefit from the use of high-efficiency rooftop units, while larger buildings may use magnetic bearing chillers. In either case, the equipment contributes to net-zero-energy status by being capable of very high efficiencies at part-load conditions.”
The first step in achieving ZNE is to dramatically reduce the heating and cooling load, said Tryson.
“Variable-speed drives and compressors can also contribute to ZNE status by offering significant payback that can range 30-40 percent. HVAC equipment is reaching the point of ‘max tech,’ or, essentially, diminishing returns on the amount of efficiency gains that can come from discrete components.”
Other HVAC systems used in ZNE buildings may include chilled beams, radiant in-floor heating, radiant ceiling panels, variable refrigerant flow (VRF), and dedicated outside air systems (DOAS). In fact, the argument could be made that just about any type of HVAC system can be used in a ZNE building, provided it is designed properly. What really separates a ZNE building from a traditionally constructed one comes down to creativity, said Torcellini.
“The traditional method is that the architect designs a beautiful building, then hands it to the engineer, who is supposed to make it energy efficient,” said Torcellini. “With a ZNE building, the process is typically inverted; the engineer is brought on very early in the process to optimize the energy aspects, then the architect works within the constraints. What you’ll find is that the architect will be creative and design a beautiful building within those constraints. Contractors are also part of this creative process, and they need to bring solutions to the table.”
The world is changing, added Torcellini, and the way of the future is ZNE buildings. “Manufacturers are delivering higher-efficiency products that help achieve ZNE. Engineers, architects, and contractors are figuring out what it takes to achieve ZNE. The solutions may change as new technologies emerge, but the survivors in this industry will be those who can think creatively.”
Publication date: 5/4/2015