News Article
October 29, 2010

Some Smart Buildings Scoring Zero on Energy Use

Hedge in the shape of a Zero representing zero energy buildings

One of the most promising benefits derived from smart buildings and a smart grid is the coordination and integration of many types of energy resources. Renewable energy systems, energy storage, combined heat and power applications and a host of energy loads can now be tied together in a meaningful way. The result is a big reduction in energy and carbon footprint. As buildings become smarter, there will be more instances of net zero energy buildings, an important part of the low-carbon economy of the future.   

 

Approaching Net Zero

Many initiatives, including the U.S. Environmental Protection Agency’s ENERGY STAR program and the U.S. Green Building Council’s LEED rating system, encourage increased energy efficiency in buildings – typically stated as a percent improvement (20% more efficient than a conventional building, or 40% more efficient than ASHRAE 90.1-2007). Such relative improvements save energy and reduce environmental impact, but they lack the simplicity and inspiring vision of an absolute goal like “zero.” They also do not guarantee energy sustainability, since even a growing number of more efficient buildings can still burn fossil fuels and produce excessive greenhouse gases far into the future.

 

In pursuit of energy efficiency and sustainability, net zero energy buildings (ZEB) are an exciting ultimate goal. A ZEB is a residential or commercial building that consumes a net total of zero energy from nonrenewable sources (such as utility electricity, natural gas, or oil). These buildings are so energy-efficient that they can rely mainly on renewable energy generated on-site. They typically use grid electricity at times of the year when renewable energy generation is not sufficient to meet demand. But at other times, on-site generation is greater than the building’s needs, and excess electricity is exported to the utility grid. Over the course of a year, the cumulative grid electricity consumed is offset by the excess generated for others to use. A small but growing number of ZEBs exist throughout the world, and policies and programs are emerging to support their widespread adoption.

 

Zero Energy Building Policy

A number of programs and policies now encourage zero energy buildings. In the European Union, a March 2009 resolution required that, by 2019, all newly constructed buildings produce as much energy as they consume on-site. Also in March 2009, a Zero Net Energy Buildings Task Force created by the U.S. Commonwealth of Massachusetts released a report detailing strategies for universal adoption of zero net energy buildings for new construction by 2030. The U.S. State of California’s Long Term Energy Efficiency Strategic Plan, adopted in September 2008, calls for all new residential construction to be zero net energy by 2020 and all new commercial construction to be zero net energy by 2030.

 

At the national level in the U.S., the U.S. Department of Energy’s Net-Zero Energy Commercial Building Initiative (CBI) aims to achieve marketable net-zero energy commercial buildings in all climate zones by 2025. Further, Section 422 of the Energy Independence and Security Act of 2007 charges the CBI to “develop and disseminate technologies, practices, and policies for the development and establishment of zero net energy commercial buildings for:

  1. Any commercial building newly constructed in the United States by 2030;

  2. 50 percent of the commercial building stock of the United States by 2040; and

  3. All commercial buildings in the United States by 2050.”



Common Features of Existing Zero-Energy Commercial Buildings

Current zero-energy buildings tend to share a number of characteristics and design concepts: 

  • They are not large – Of eight known zero energy buildings in the U.S., all are one or two stories tall and comprise less than 15,000 square feet. As technology advances, this may change. However, energy modeling performed by the National Renewable Energy Laboratory and the U.S. Department of Energy (DOE) shows that—at present—it would be harder for three-story buildings to meet ZEB goals with on-site resources and extremely difficult for buildings of four or more stories to do so. This is because multi-story buildings have relatively higher load densities, relatively less roof area for PV systems, and relatively less daylighting potential. Although this may appear to be a major limitation of ZEB design, it does not affect most U.S. commercial buildings, which on average are one story and 8,000 to 16,000 square feet.

     

  • Efficiency first - Energy saved in a ZEB is energy that the building doesn’t have to produce. An effective whole-systems methodology to achieve maximum building efficiency takes the right steps in the right order:

    • Load reduction: Reduce every energy-consuming load to the minimum and eliminate unnecessary loads. In a new building, start with a design that includes only the energy services that are actually necessary.

    • System efficiency: Meet the remaining loads as efficiently as possible. Optimize the efficiency of the system as a whole, in addition to the individual components. (For example, specify highest efficiency system of chillers, pumps, motors, and fans.)

    • Regenerative systems: Use waste energy for useful purposes.

    • Renewable systems: Generate power on-site and renewably. One notable effect of extreme efficiency is that, as lighting and HVAC systems get more efficient, plug loads become relatively more important and a more significant target for reduction. Thus, choosing the most energy-efficient devices becomes essential to achieving net zero energy use.

  • Integrated design and operation are necessary - Zero-energy buildings achieve their goals best when all parties involved – from owners to architects to contractors – share the zero-energy vision and collaborate throughout design and construction. Further, facility operators and building occupants, who control system settings and plug loads, must actively participate to make the building achieve its design goals.

     

  • On-site renewable energy is a priority - Renewable energy generated on-site has the most permanence over the life of the building and leads to the fewest grid losses. The inherently smaller unit size and shorter lead times compared to utility-scale renewable energy also result in a variety of economic benefits, including improve system reliability, ease of siting, lower debt service, and better capture of learning curve effects, amongst others, The closer the distributed resource is in location and scale to end-use load, the better it can match the pattern of the load, thus maximizing the avoidance of costs, losses, and idle capacity. Strategically placed onsite renewable energy systems can also make the most stressed parts of the distribution grid more stable.

     

  • Grid connection makes it possible - Of eight known ZEBs in the U.S., all but one rely on grid connections to achieve their annual energy balances. These buildings provide a useful service to the utilities, since they use less power (thus reducing demand) and produce excess power at what tend to be the utility’s peak usage times of the day and year. Grid-independent buildings that achieve net-zero status must rely on fairly expensive storage technologies. It is less expensive and more convenient for the owners to be connected to the grid.

     

  • Monitoring and verification prove the achievement - Once a ZEB is in use, careful monitoring and verification are needed to back up the design claims and, often, to identify and correct improperly constructed or functioning systems. The owners of buildings that share this monitoring data are helping to disseminate actual information about the performance of ZEBs, which should reduce the risk and accelerate construction of new ZEBs.

     

October 2010

 

 

1 Zero Energy Buildings: A Critical Look at the Definition [http://www.nrel.gov/docs/fy06osti/39833.pdf].

 

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