Exploring the Very Real Possibility of Net-Zero
Grid neutral. Carbon neutral. Net-zero energy. You’ve probably heard these terms and can infer from context what they mean. Let’s skip the inferring, though, and get specific.
According to a tip entitled, “Understanding What a Net-Zero Energy Building Really Is” (accessed 3/6/13), posted on Facilitiesnet.com, there are four main types of net-zero energy facilities. The first is net-zero-site energy buildings, which produce at least as much energy (through on-site renewables like wind turbines and solar array) as they use on a yearly basis. The second, net-zero-source energy buildings, produce as much energy as they use when calculated at the source, which means that the “building’s produced energy must also make up for energy lost in transmission from the source of the energy the building does use.” Net-zero-energy cost buildings, the third type, “are those in which the amount of money an owner pays for electricity a building uses is equal to the amount of money the utility pays the owner for renewable energy the building feeds to the grid.” And the fourth type of net-zero-energy facility is net-zero-energy emissions, in which the “buildings produce and export at least as much emissions-free renewable energy as they import and use from emission-producing sources on an annual basis.”
La Escuelita Education Center, for example
There are now a handful of net-zero energy schools across the country, and more are going on the boards all the time. One that is in phase two of construction — expected to be complete in fall 2014 — is La Escuelita Education Center, a project of the Oakland Unified School District (OUSD) in California. Sited on 5.7 acres, the 123,000-square-foot project integrates four schools in one facility that includes La Escuelita Elementary, MetWest High School, a child development center that replaces Yuk Yau and Centro Infantil child development centers, a great room (serves as cafeteria, gymnasium and multi-use space with a stage shared by all schools) and a community health clinic.
According to the OUSD website, the high school serves 180 students in a two-story complex designed around a double-height town hall space, the child development center serves 168 students in seven classrooms and there is also a designated kindergarten play area, shared play field and community edible garden. Oakland, Calif.-based SUDA/ADCo, in joint venture with Turner Construction, serves as the construction manager and indicates on its website www.sudallc.com that the project value is $75 million.
That’s a lot of information, and it begs the question: What about this complex makes it net-zero? For that, we look to the complex’s architect, Oakland, Calif.-based MVE Institutional, and energy news source ENR California, california.construction.com. We find that it begins with the building’s orientation, which maximizes north-south exposure, leveraging daylight access while controlling solar heat gain. With this exposure, the architect designed a 40-percent window-to-wall ratio along the north elevations, a 30-percent window-to-wall ratio along the south elevations, limited glazing along the east and west elevations, and specified operable windows to allow natural ventilation in each classroom.
Next, roof-mounted photovoltaics on all sloped roofs convert sunlight into energy for on-site electricity. This includes photovoltaic panel shade structures placed on an on-grade parking lot.
Cooling is accomplished in a number of ways. Oversized ceiling fans and a displacement ventilation system are used within classrooms and administration spaces to bring in cool air close to the floor level at low velocity and at a temperature below the room temperature. Passive evaporative cooling towers use integrated misting systems to provide cool air to large common areas with minimal energy use. Plus, a medium thermal mass wall system achieves 100-pounds-per-foot3 density to eliminate the need for compressorized cooling.
Energy performance will be monitored by a comprehensive building management system, the data of which will be used to fine-tune systems for optimal efficiency.
Achieving net-zero energy on your project
“Carbon neutrality, net-zero, whatever you call it, is going to be the way everybody will judge the success of sustainability strategies for school districts,” says John Gautrey, PE, LEED-AP, a principal with Sherman Oaks, Calif.-based IBE Consulting Engineers. “Schools are public institutions by their very nature, and the public more and more desires that institutions be accountable from an energy perspective. As energy prices increase, there will be a financial reason to go carbon neutral as well.”
That said, there are a number of strategies available to help administrators at least reduce, if not eliminate, energy consumption. Here are a few that the experts have to offer.
1. Siting and minimizing: “I think where you start is where you start on any other building,” Gautrey says. “You have to site and design the building to minimize energy use in the first place. This includes proper shading and glass walls facing west.”
Gautrey also advocates an understanding that reducing the HVAC load is only part of the strategy. HVAC is between 25 and 33 percent of a building’s energy use, and flood and loading light are equally, if not more, important to consider when designing a net-zero building. “You have to weigh an efficiently performing façade against maximizing daylighting to reduce lighting loads,” he says.
2. Offsetting energy use: Next, you have to evaluate the different strategies available to offset energy use. This is partly driven by local climate and requires a cost-benefit analysis before making a decision. For example, a school located on a coast can probably eliminate an HVAC system altogether in favor of natural ventilation and energy produced by wind. Similarly, you may choose photovoltaics, especially if you’re in a sunny climate and have available roof space.
3. Fans: When it comes to using fans, there are three main ideas. The first is de-stratification, in which the air is blended so the HVAC unit doesn’t cycle as often. The second is the ability to reduce the HVAC set point during the cooling season. In fact, fans moving at a slow speed and moving a large volume of air can reduce the temperature set point about four degrees. The third is reduction in duct work, a result of fans offsetting the air needed to be forced through duct work by the heat pump.
Isaac Fedyniak, PE, LEED-AP BD+C, CEM, NABCEP PV, an electrical engineer with Lexington, Ky.-based Big Ass Fans, discusses Locust Trace, a net-zero high school in Lexington. “In the winter,” he says, “a thermal solar system provides radiant heating. We raised the heating equipment to 12 feet above the floor so that it wouldn’t be damaged by students or equipment, and we use a fan to circulate the heat down to the occupant level.”
4. Window coverings: When considering window coverings, there are three primary goals, says Christopher Hagen, regional sales manager for Dallas-based Hunter Douglas. First, remember that you’re specifying to achieve solar control. Second, to gain more significant LEED contributions, choose motorized coverings. Third, consider wand control or a crank to protect against cord choking hazards.
Hagen cites Lady Bird Johnson Middle School in Irving, Texas, the largest net-zero public middle school in the country. “We used RB 500 motorized roller shades to minimize the need for artificial lighting and manage solar heat gain to reduce loads on the school’s HVAC systems,” he indicates. Motorized controls allow all 33 shades in the cafeteria and library to operate through a single wall switch in each room. Combined, all 33 motors spin together on just 28 amps — less energy than required to run a standard refrigerator.
Grid neutral. Carbon neutral. Net-zero energy. Whatever you call it, it’s real. And it’s here to stay.