This is a report on the zero emissions building virtual design charrette that took place in HOK’s Advanced Collaboration Rooms in San Francisco, Toronto and St. Louis on 13 August 2009.

This virtual meeting’s participants included Bill Valentine, Tim Gaidis, Tyler Meyr, Gerry Faubert and Jeff Sanner of HOK along with Prasad Vaidya of The Weidt Group. Ideas were flying, and the electronic flipcharts received a heavy workout. Here’s a summary of the outcomes.

Bar Length, Alignment and Core Configuration

Previous energy efficiency and generation models had demonstrated that it would be tough to meet the zero emissions goal if the total building area surpassed about 180,000 square feet. “If we need to increase the building area, we will need less floors,” said The Weidt Group’s Prasad Vaidya.

The team refined the building’s bar length and alignment and settled on a basic core configuration for the two 300-foot-long bars.

“The 330 feet we have been working with recently is very long,” said HOK St. Louis Sustainable Practice Leader Tim Gaidis, who explained how to fit core elements including air handling rooms, electrical and telephone equipment, stairs, elevators and toilet rooms into 300-foot-long building bars.

HOK Chairman Bill Valentine drew from his half-century of architectural experience to suggest detailed options for the building core. At one point he helped make it work by reducing the amount of sinks in the restroom. Every detail counts – even the not-so-glamorous ones – when designing for zero emissions! After making a few design refinements that helped cut the bar length of each building down to 300 feet, Valentine complimented Gaidis’ work and advised the team to “call it a day” and move forward with the plan.

Photovoltaic Panels on the Roof

The team discussed whether the building’s roof would need to be sloped or oriented at latitude to accommodate the required amount of photovoltaic panels.

“If we need to slope the PV panels, we will have fewer area to work with because there needs to be space between each panel,” noted Valentine. “If the two bars are each 300 by 64 feet, that gives us 37,000 feet of roof space. We’ll be lucky to get 24,000 square feet of solar panels there. We’re also going to need solar panels running down the south elevations of both bars and another 10,000 to 15,000 square feet on the roof of the parking garage.”

Vaidya advised the team to wait until the daylighting analysis was complete to make any decisions about a sloped or flat roof.

Post-Tension Concrete Slab Thickness and Floor-to-Floor Height

Another topic was the post-tension concrete slab thickness for the two-story parking garage and the office building.

Valentine reported talking to structural engineers who had advised that the design of a 28-by-30-foot bay garage could use eight-inch post-tension slabs – and that they could use 8 ½-inch post-tension slabs in an office building constructed with 30-foot spans. “They believe it will take the least concrete to do that,” he said. “It won’t affect our energy calculations but it does reduce cost and embodied energy.”

Based on using a an eight-and-a-half-inch concrete slab, a potential 10-inch ceiling drop for chilled beams and 14 inches for the raised floor, the team settled on a floor-to-floor height of 16 feet, with 14 feet at the perimeter — another example of every inch counting when shooting for zero emissions.

“This will allow us to naturally light everything in an economical way,” said Valentine. “It’s a little high but we could sell it to a developer.”

Parking Garage: To Automate or Not Automate?

The team explored the pros and cons of using a mechanized parking garage that would automatically pick up, move and park the vehicles.

The team agreed that they could make an “embodied energy” argument that this automated garage – which the manufacturer estimated would cost $26,000 per car – would, when compared to a typical two-level parking garage, reduce auto emissions and use less land, concrete and materials.

A mechanized garage also would free up space on the site for a potential housing and expansion strategy to the south that would create a truly mixed-use development.

But Vaidya pointed out that the mechanized garage would increase energy use on the site by up to two-thirds. “That automated mechanism uses a lot of energy,” he said. “We want the building not to consume more than 18 KTBUs per square foot. Adding this mechanized garage alone is equivalent to 12 KTBUs per square foot of building area. This takes the energy budget from 18 to 30 KTBUs. So by extending the definition of zero carbon to include cars waiting at the garage entrance, we would be expanding the realm of our problem while keeping the solution set the same.”

Though the automated garage offered environmental and economic benefits, Tyler Meyr of the HOK Planning Group in St. Louis conceded that, “The reality is we won’t be able to make a zero energy building on our site if we use a mechanized garage. The challenge gets much harder.”

“Then we shouldn’t do it,” concluded Valentine. “Our goal is to show we can get to zero emissions without too much time or trouble.”

The team agreed to acknowledge the larger problem of land use and auto emissions by keeping the automated garage in the study as an option that did have some merit.

The team then proposed solutions for daylighting the 400-car parking structure with a photovoltaic canopy structure.

Solar Thermal or PV Panels on the Facade

The team analyzed the possibility of using solar thermal or photovoltaic panels on the building’s south facade.

We don’t yet know the optimum mix of photovoltaic and hot water panels,” said Vaidya. “We need to figure out the final energy consumption of the building before we decide on that proportion.”

HOK Director of Integrated Design Gerry Faubert pointed out that not much much roof surface area will remain for solar thermal panels after the required photovoltaic panels are put in place. “I think this is OK because in a typical office building we do not have a high domestic hot water load,” he said. “The bigger issue is producing power from the PV panels.”

“But we can still use hot water to provide space heat,” responded Vaidya. “We want to use low grade heat sources to provide low grade heat.”

Because the solar thermal water panels don’t have to be on a flat surface, they could be placed on the rain-screen cladding of near the top of the building, said Gaidis. “With the lower sun angles in the winter, we would only be able to use them on the upper levels of the building’s south side.”

Vaidya suggested that the south-facing cladding material could be light-colored in order to reflect light into the other bars and into the building courtyard.

Looking Forward

Window daylighting sketch

At the next meeting the team will explore the final energy and daylight modeling analyses (including costs). “Chris is still working on modeling more than 100 strategies for energy conservation,” said Vaidya. “Vinay is doing annual daylighting analyses.”

Another as-yet unanswered question is what type of mechanical system to use for the building.

“At the end of the day, the system we choose and the energy efficiency level we achieve will determine the amount of renewable energy we need on the site,” said Faubert.

Questioned about the potential for a chilled beam system, Faubert deferred, saying the team needed to wait for the results of The Weidt Group’s energy analyses, “But it is a safe bet we will have a raised floor and under-floor air distribution system here,” he said. “And whatever we can do in terms of using a chilled beam as primary cooling system – coupled with the raised floor – will produce good energy results.”

To the dismay of some, Faubert also reported that the prospects appeared dim for including operable windows with this type of chilled beam system. “While I won’t discount the idea, the humidity levels in St. Louis will probably create too much of an energy load.”

Previous ZEB posts:

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