This is a report on the zero emissions building design charrette that took place on September 17. HOK and The Weidt Group participants in San Francisco, Toronto, St. Louis, Berkeley, Calif., and Minneapolis saved carbon emissions from air travel by using Cisco Telepresence Technology, Polyvision THUNDER Express, WebEx and HOK’s Advanced Collaboration Rooms to meet virtually.

The team designing the a zero carbon emissions office building has made lots of progress since my last ZEB post. With the final meeting fast-approaching and an affordable carbon-free solution on the horizon, it’s time to crank out some posts to catch you up on what they’ve been up to.

Finally, a Focus on the Building Design

After exploring different energy models during the first few charrettes, the focus of this meeting was on the building design. “It’s time to start thinking about what this building will look like,” said HOK Director of Sustainable Design Mary Ann Lazarus.

The team was still riding the high from a September 10 teleconference in which, after a brief period of doubt, they discovered that they could develop a bundle of energy conservation strategies that would satisfy the team’s original 10-year payback goal for the zero carbon building.

“Let’s do our best to keep driving down the costs,” urged HOK Chairman Bill Valentine. “Our goal is to be able to say that developing a zero carbon building is no more than 10 percent more expensive than a conventional building. That’s how we can mainstream this. My fatherly plea is for every design decision we make to be purpose-driven.”

The Weidt Group’s bundles of energy conservation strategies showed that the zero energy and zero carbon solutions would be quite different – a development that surprised some. These differences demonstrate that the process the team has developed, which they hope to share with the world to encourage more zero carbon designs, will generate varying results based on a project’s specific carbon emissions, energy reduction or payback goals.

Many of the systems solutions also are location-specific. In St. Louis, for example, the location of this project, 80 percent of the electricity is generated by coal-fired power plants. HOK Director of Integrated Design Gerry Faubert pointed that in other regions where energy is 80 percent hydro-generated, for example, the decisions and solution sets would be quite different.

The Weidt Group Energy Analyst Chris Baker acknowledged that most of the team’s decisions had been site-dependent, but sounded a caution about over-generalizing: “Whether we are talking about the utility grid, the weather data or the building shape, many factors have come together to lead us to our specific solutions.”

Sloping the Roof

One big question affecting the section design was how to best place the required solar panels on the approximately 40,000 square feet of roof area available between the two bar buildings.

After exploring a thin film product that could be directly integrated into the roofing system, the team ultimately decided to use traditional crystalline solar panels. Though the costs per kilowatt would be about the same, the major difference is that the thin film product would take twice the roof area to produce the same amount of power as a fixed crystalline, solid glass panel.

“We need 44,000 square feet of traditional crystalline solar panels and 17,000 square feet of solar thermal generators for the zero carbon energy conservation bundle we selected,” said Baker.

After determining that it would not be considered “cheating,” the team decided to use the parking structure’s roof to house the 4,000 square feet of PV panels that would not fit on the building roofs.

“We are designing a building for the St. Louis climate,” noted Faubert. “I’d be willing to bet that, with our solutions, we would not need more than 40,000 square feet of photovoltaic panels in most locations in the continental U.S. Not many jurisdictions have so much of their electrical energy generated by coal.”

Led by Valentine, the team spent 30 minutes sketching concepts that modestly sloped the roof of both bar buildings to accommodate the most efficient placement of the crystalline panels. Lowering the roof’s southern side by three feet and raising the northern side by three feet, for example, would create a 10 percent slope with nearly the same amount of building skin—but this would allow more daylight to enter from the north and less from the south.

Valentine sketched his idea for the roof:

“Laying the panels on the roof surface could conceptually feel like part of the overall form versus an additive thing,” said the HOK Planning Group’s Tyler Meyr. “It would reinforce that this is a full building approach.”

“Having a top floor with office space inside a garret will be attractive to the market,” said Valentine. “And water could come off the side of the building and go into cisterns without any roof drains. It’s a purpose-driven decision that’s good for the market value and for the environment because it is simpler construction that requires less materials. Let’s do it.”

Of course in the design of a zero carbon emissions building, every seemingly minor decision about the building envelope has important energy use and daylighting ramifications.”Our intuition is that this could work but we’ve learned that we need to verify the science,” said Lazarus.

The Weidt Group Principal Prasad Vaidya performed an on-the-fly calculation: “If we place the photovoltaic panels on top of our two bar buildings at latitude at a 20-degree slope, it is only three percent reduction in power generation over the year.”

But would the desired 100 percent daylighting solution still work with this configuration?

“In this solution we would lose light compared to having flat ceilings on both sides,” responded The Weidt Group Energy Modeler Vinay Ghatti. “Our original direction for energy optimization throughout this process has been to maintain daylighting as much as possible. Daylighting first, then thermal efficiency.”

Faubert suggested introducing light tubes to provide soft daylighting in some areas.

“Then you are adding non insulated penetrations in roof,” said Vaidya. “We need to test the effect of adding more glazing.”

The team resolved that The Weidt Group would study the impact on thermal efficiency and daylighting of a 10-15 percent roof slope. “It’s simply an optimization exercise to find the right angle,” added Vaidya.

Green Walls

Meyr suggested planting green walls on the ends of office bars. A structure behind the greenery could have a self-watering system that would show up as a gridded pattern when exposed.

“We need to verify the energy numbers, but my intuition is that this is a home run idea,” said Valentine. “It’s a seasonal solution that puts oxygen back into the atmosphere.”

“I would like the ends of the links to be distinct from the east and west ends of the office bars,” said HOK St. Louis Sustainable Practice Leader Tim Gaidis. “Using the same green plantings would confuse the clarity of the massing in the courtyard.”

“We could do different plants with more color,” agreed Meyr. “It should be differentiated.”

Valentine recommended adding small slot windows to help further scale the massing of the end blocks and add some daylight.

The ACR in action:

Solar Thermal Tubes

Gaidis suggested that another skin element could be solar thermal tubes placed vertically on the south facades of the bar buildings. This “technical” skin would provide a heat source for the hot water system and add visual interest.

Previous ZEB posts (in chronological order):

1. Onward to Zero Emissions
2. Onward to Zero Emissions – Part 2
3. Weidt Light
4. Zero Emissions Building Charrette #2 — The Paradigm Shift
5. Passing Virtual Notes
6. Zero Emissions Building Team Using Biomimicry as a Design Filter
7. Challenging the Frontier of Carbon Neutrality
8. Zero Emissions Building Charrette: Bar Length, Core Configuration + More!
9. Zero Emissions Charrette: Reviewing the Energy Design Strategy Report