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Marc Brune has a lot of weight on his shoulders. As the associate in charge of energy modeling for both the Oregon Sustainability Center and the Cascadia Center for Sustainable Design and Construction, he will help determine how many photovoltaic panels are needed to power the buildings, which are expected to achieve net-zero energy consumption.

But energy modeling is not only for ultra-green buildings; the practice has become increasingly common in the last decade, said Jeff Kline, research associate at the University of Oregon’s Energy Studies in Buildings Laboratory.

Some of the increased demand for energy modeling comes from requirements for Leadership in Energy and Environmental Design certification and Oregon’s State Energy Efficiency Design programs, Kline said. 鈥淎nd some demand is driven from the market, as firms look for more services they can offer to distinguish themselves from their competition,鈥� he said.

Kline said that the UO lab doesn’t perform energy models for architects as much these days because engineering firms, or architects themselves, are meeting the demand.

鈥淲e got into a phase a few years ago where there just weren’t enough modelers to go around. And you had a bunch of people practicing that weren’t all good at it and there weren’t best practices established,鈥� said Craig Briscoe, associate at ZGF Architects.

Designers use energy models to compare benefits of design or technology options and to meet certification or code requirements for energy reduction.

Once a building is occupied, an energy audit can generate vastly different results than predicted by the energy model; however, accuracy is not exactly the point, Briscoe said.

鈥淭he intent behind an energy model is to use it as a design tool, to look at a number of options for energy-efficiency measures and then choose the best one. Predicting absolute energy use is not the goal,鈥� Briscoe said.

Modelers such as Brune use special software to create building energy models. Many factors are considered, including measurements and orientation, local weather, and every sort of energy use. The work can require from one to two weeks, depending on the experience of the energy modeler and the software being used. The process is often repeated multiple times during the design process.

Ultimately, a model can be only as accurate as the information entered. Briscoe cited a Pacific Northwest higher-education building built by ZGF that was modeled to have energy usage at 45 percent below the baseline building standard. A post-occupancy energy audit showed that energy use in the building was nearly twice the amount expected.

鈥淭here were questions,鈥� Briscoe joked.

The model for that building had inaccurate information about 鈥減lug loads鈥� 鈥� energy used by computers, space heaters, lights and other appliances brought in by users.

鈥淧lug loads have been increasing through the years, and it’s very difficult to get a good prediction of that,鈥� Kline said.

鈥淧lug loads are one of the things you have to try and govern,鈥� Briscoe said. 鈥淥wners will be resistant; how useful is a building if you aren’t allowed to plug in as much as you want to?鈥�

Existing net-zero buildings are mostly owner-occupied, so use is easier to control. The Oregon Sustainability Center, however, will have multiple tenants.

鈥淭he first inclination is to throw a heavy safety factor on the model,鈥� Brune said. 鈥淏ut photovoltaics are very expensive, so there’s pressure to reduce that safety factor.鈥�

Brune also must account for how much energy the building’s solar panels will actually produce, because advertised specifications may be exaggerated.

鈥淢anufacturers spin it as much as they can,鈥� Brune said.

Ultimately, the modelers, like the rest of the design team, must wait for monitoring and metering systems to measure buildings’ energy use.

鈥淚t’s going to be pretty wild to track it all and try to bring it home to net-zero after 12 months,鈥� Brune said.