The second zero emissions building design charrette took place July 23 in The Weidt Group’s naturally daylit offices in a Minneapolis suburb. The brainstorm team included five designers from each firm, with combined expertise in energy and daylighting modeling, architecture, engineering and integrated design. Click here to see the agenda.

The team began by restating its goal: To design a 150,000-200,000-square-foot, high-end speculative office building in St. Louis that is a zero emissions building (ZEB). The group also wants to document a process that could potentially change the way they design buildings.

HOK Sustainable Design Director Mary Ann Lazarus clarified the team’s definition of a zero emissions building: “The goal is for net zero annual emissions. So we will produce enough emissions-free energy on the site to make up for any energy we are consuming there in a year.”

The team met in Minneapolis to analyze the zero emissions potential of the project before it moved too far into design. The group wanted to quantify preliminary energy results, to get a feel for how energy efficient the building could be, and to explore potential solutions for reaching zero emissions in a way that would be both doable and quantifiable.

Weidt Group Principal David Eijadi urged everyone to drop all their preconceived ideas about the building and to remember that, like Star Trek’s Scotty used to say, “We can’t change the laws of physics if we don’t like the answer.” That emerged as a theme for the day.

The team agreed that while the design solution would need to be incredibly innovative to meet the zero emissions goal, all systems and strategies would need to be marketable, proven and economically viable. “If you are going to make something complicated, you better have a really good reason,” said Eijadi. “We need to keep in mind solutions that are proven and close at hand.”

“We will use a cyclical process,” said charrette facilitator Prasad Vaidya, who heads The Weidt Group’s LEED consulting practice. “We will create models of virtual buildings, measure them against expectations, manage our expectations and keep modeling until we get a real building that works.”

BRAINSTORMING EXERCISE

The group began by brainstorming strategies that could contribute to a zero emissions solution.

There was no shortage of ideas. The team quickly generated a laundry list that included on-site wind power, geothermal integration with heat exchanges, solar thermal absorption cooling, desiccant cooling, solar thermal heating, capturing condensate through shape modulation, solar thermal heated desiccant, natural ventilation, mixed-mode ventilation, seasonally applicable technology and operation, layering of skins and zones, variable perforated movable skin, green roofs, filtering ventilation air through vegetation or mass, switchable glazing, water-filled mullions, and wax-filled glass micro beads.

“On a typical project, we would delay the creation of this list until the architecture was further along,” explained Vaidya. “But the team needs this information earlier to reach the zero emissions goal. It’s a starting point so we can understand the impact of all the components as we do the design.”

CLIMATE AND CONTEXT STUDY

A climate and context study looked at the daylighting climate and the result of the St. Louis latitude and office building type on shading solutions. With 150-180 cloudy days a year classifying St. Louis as an “overcast sky” climate, the team learned that they would need to design the building with 18-22% window-to-floor area to achieve the minimum 1.5-footcandle daylight factor.

The group studied the generation potential of different building surfaces for different types of solar panels. It was clear that roof surfaces would be far more effective than wall surfaces in producing energy.

For the temperature and thermal comfort analysis, the group reviewed wind roses and psychometric charts for St. Louis and determined the thermal comfort requirements for each of the four distinct St. Louis seasons.

The climate and context study included an examination of what percentage of the occupied hours the building could be naturally ventilated.

ENERGY EFFICIENT BUILDING STUDY

The next major task was to do some zero energy pre-design scoping. The Weidt Group used its Net Zero Energy Tool to analyze the impact on construction costs of increased energy efficiency and renewable energy for four possible options, compared to a base case building with 100% non-renewable energy.

An energy generation and building massing study revealed that a photovoltaic system had the most potential for providing renewable energy on this site.

The group reviewed the energy results of a Weidt Group simulation to understand the opportunities for energy efficiency before breaking into three breakout groups focused on creating the most appropriate energy efficiency strategies for the massing and envelope (glass, insulation, etc.), HVAC systems (type, solar thermal, photovoltaics, etc.) and plug loads.

“Plug loads will a huge variable in a zero emission, multitenant speculative office building,” noted Lazarus. “We can’t afford to let them float.” The team made assumptions that the plug loads will be 50 percent lower than normal for an office building, and explored strategies for reducing energy use and modifying occupant behavior through a ‘carrot and stick’ approach. They looked at options for metering and tracking usage for each tenant.

This exercise provided an interesting lesson on thinking about massing and systems together, said Lazarus. “For a long time, we as sustainable architects have been pushing the passive solutions first — doing everything we can do to the envelope without using a switch or a fan. But for a zero emissions design there is great value in thinking comprehensively about the massing and the systems as well as occupant behavior and plug load parameters.”

ZEB GOAL: AN 80 PERCENT EFFICIENT BUILDING

The team concluded the day with the understanding that the design will need to reduce the energy requirements for a typical St. Louis office building by 80% to meet the zero emissions goal.

“That was the big takeaway,” said Lazarus. “We think we can get the rest of the way to zero through on-site renewable energy sources — primarily photovoltaics with some solar thermal systems.”

“We have done 60 percent before,” noted Eijadi. “Seventy percent is doable, but you are starting to reach. Bringing down the total load by 80 percent while using current technology will require a whole new type of architecture.”

NEXT STEPS

HOK’s team committed to continuing to develop the architectural expression of the building, which includes generating four massing models to scale and daylight analyses of the proposed schemes, and an Ecotect analysis. HOK also is producing a site study of the four massing models and baseline cost models for each.

The Weidt Group is going forward with energy simulation analyses and studying mechanical options for the four proposed building geometry schemes.

THE PARADIGM SHIFT

Interspersed throughout the day’s activities were conversations about making fact-based, instead of emotional, decisions. The Weidt Group’s participants continuously emphasized that the best way to design zero or low emissions buildings is to respect the physical limits of the universe.

“It is entirely possible to design a zero energy building,” said Eijadi. “It has been for a long time. But you have to do it by looking at the numbers faithfully and understanding what they mean. A building can’t be just any size or shape. Some architects are afraid of those constraints because they think they will inhibit design. But they simply inform design.”

Vaidya stressed that the energy models are a tool that provides designers with the right information to make decisions. “Within those numbers lies the freedom of design.”

“Decision-making is part of what makes designers great and we need creativity, added Eijadi. “But you should know when you are making an aesthetic decision versus a science-based decision and be very clear about which is which. Only then we can make decisions to get the building we want.”

HOK St. Louis Sustainable Design Practice Leader Tim Gaidis agreed that architects can be guilty of using too many assumptions or intuitions gained over time. “There is a clarity brought to the decision-making process by having the metric analysis and by holding off on the emotional or subjective decisions or aspirations until you understand the baseline information,” he said. “You can always make those emotional decisions later. But if you jump to those first, there is no way you can catch up and let that technical information inform the building at the high level that it should.”

Eijadi pointed out that aesthetic decisions made with the best intentions may seem perfectly fine, but if they compromise performance — by event a very small amount — those failures will be multiplicative. “Every little thing counts in a zero emissions building design. It’s death by a thousand cuts.”

The group agreed that achieving clarity on the cause and effect of making individual component performance decisions to reach a zero emissions building will be part of the paradigm shift.

“The dilemma now is how to develop the design,” said Lazarus. “So far the massing options we have created are not architecture, but they could be. We want to the architecture to be informed but not designed by the model. There is something there that needs to be interpreted. That is the challenge.”

Next virtual charrette: 31 July 2009.

Previous ZEB posts:

Onward to Zero Emissions

Onward to Zero Emissions – Part 2

Weidt Light