The concept of a net-zero energy building isn’t exactly new. Over the past 10 years several examples have been developed around the U.S., many of which come in at well under 10,000 square feet. But, the opening of the 220,000-sq.-ft. National Renewable Energy Laboratory’s Research Support Facility in Golden, Colo., earlier this year is showing that large-scale office buildings with hundreds of occupants also can achieve net-zero energy use.

In the past, these buildings might have been seen as a novel experiment in green design; today, they are recognized as one route toward creating sustainable building stock.

Achieving net-zero

For many, “net-zero” might conjure images of solar panel-laden rooftops and on-site wind turbines. Although zero-energy buildings certainly include such on-site renewable energy sources, they are only one component — and in many ways the secondary component — of achieving net-zero energy use.

“The first piece is that you want to save a lot of energy because saving energy is always more cost effective than producing it,” says Paul Torcellini, Principal Group Manager for Commercial Buildings Research at the National Renewable Energy Laboratory. To achieve net-zero at the Research Support Facility, the organization set an aggressive stand on how much energy the building would use.

“If I take a look at the building and look at the loads, the first two things that stick out in most commercial office buildings is lighting loads and the plug loads,” Torcellini says.

Essentially, plug loads represent what people bring into a building and plug into an electrical socket. To reduce the plug load at the new facility, as much as three years prior to the move NREL began buying laptops when employees needed a new computer. Other simple measures include using six-watt desk lamps and two-watt telephones, as well as installing a single combination copy, fax, scan and print machine in each wing of the building — and no more. The design of the building itself allows for extensive natural daylighting, meaning there is no need for electric lighting between 9 a.m. and 3 p.m.

“All of that is real stuff in terms of sustainability,” Torcellini says. “By the time we did all that and insulated the building well, there really is not much cooling load and not much heating load.”

It also means that the photovoltaics, or solar panels, on the roof of the building and parking structure are able to make up the energy requirements of a 220,000-sq.-ft. space.

The energy grid

The energy grid is one of the most important players in the net-zero game. It’s like an electron pool where a community grabs its energy. When a net-zero building produces more energy than it needs to operate, it sends the excess to the grid, essentially adding electrons to that pool. In times when a building’s on-site renewable energy is minimal, it can draw electrons from the energy pool without affecting the grid’s annual needs. Hence the term net-zero.

This can sometimes lead to a tricky electron accounting game. For instance, if the building is using energy from a utility that relies on fossil fuels, it is then pulling from non-renewable energy sources. That said, it is also not adding to a community’s need for non-renewable energy. And as more and more parts of the country embrace renewable energy, the amount of net-zero buildings occasionally relying on fossil fuels likewise will continue to dwindle.

Take the case of the Adam Joseph Lewis Center for Environmental Studies at Oberlin College in Oberlin, Ohio. One of the pioneering structures in net-zero building, the Lewis Center was completed in January 2000, and at about 13,600 square feet, it remains one of the larger net-zero energy buildings in the country. Like many net-zero buildings, it derives its power from rooftop photovoltaics, and it’s worked so well, in fact, that the building has produced more electricity on an annual basis than it has consumed. In providing this energy to the city’s utility grid, the center is essentially providing green energy to residents in the surrounding town.

And in two years, at those times when the Lewis Center does need to pull energy from the grid, odds are it will be renewable energy. According to Rob Lamppa, director of sustainability and energy management at Oberlin College, the city’s municipal utility has entered contracts that will lead to approximately 85 percent renewable energy resources by the end of 2013.

Maintaining net-zero

Creating a net-zero building is one thing, keeping it there is another. The Lewis Center is equipped with sensors for all its systems, all of which can be viewed in real-time.

“Using all of those sensors, you can monitor water use, you can monitor energy use in real time,” Lamppa says. “It will show you what the solar panels are doing; it will show you what the thermal heating system is doing; it will show you what’s happening with the living machine.”

All these sensors make it possible for the building operators to maintain the systems that keep this building net-zero. However, as a building designed to demonstrate and educate about net-zero building concepts, the Lewis Center does employ some technology that might not be cost-realistic or appropriate for all building operators.

“You want to design systems that are as simple as possible so that they don’t rely on a lot of sophistication,” Torcellini says. “A building is only going to be as smart as whoever’s operating it, and quite often I find in a lot of buildings people design in sophistication in the name of energy efficiency and then nobody really knows how to make it work.” He points out that, for instance, factories predating electricity were net-zero, employing only daylight, natural ventilation and waterpower running the machines.

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