Zeroing In on Net-Zero Energy

With an office building for its Colorado campus, a national research lab aims to prove that super-green can be cost effective and replicable.
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From Architectural Record
Joann Gonchar, AIA

Net zero defined

What is a net-zero building? At the most fundamental level, it is a building that annually generates enough energy on site from renewable sources to equal or exceed demand. Like the NREL facility, most zero-energy buildings are grid-connected, drawing power from, and supplying it to, a local utility. In the case of the RSF, a 450 kW roof-mounted photovoltaic (PV) array, supplied through a power purchase agreement with solar energy provider SunEdison, serves as the renewable source.

1 Permeable landscaping
2 Fresh air intake
3 Thermochromic east-facing glazing
4 Transpired solar collectors (not visible)
5 Photovoltaics
6 Electrochromic west-facing glazing (not visible)

7 Low-profile open offices
8 Raised floor system
9 Radiant ceiling slabs
10 Thermal labyrinth
11 Louvered sunshade

Diagram: © VStudios

Curiously, a net-zero building was not one of the highest-priority elements of the RSF program. A request for proposals released in late 2007 ranked the client's needs into "mission critical," "highly desirable," and "if possible" project goals. The document, part of a procurement process the DOE has dubbed "performance-based design-build," listed the highest level of LEED certification among the top priorities (the RSF is on track for a Platinum rating), but put net zero with those objectives under the "if possible" heading.

By establishing this hierarchy and deviating from the DOE's traditional design-bid-build delivery method, the owners hoped to encourage teams competing for the project to come up with the optimal design solution within tight schedule and budget constraints. The goal was not to build the least expensive building. "The budget was fixed, so there was no incentive to build the RSF for less," explains Paul Torcellini, NREL group manager for commercial buildings research. "Instead we wanted to achieve the best value with the money we had available," he says.

The design-build team eventually selected for the project - architecture and planning firm RNL and Haselden Construction - aimed to satisfy all of the owner's ambitions, even the items on the wish list. "We decided that if we didn't give the clients everything they wanted, we wouldn't win," says Craig Randock, AIA, RNL principal. Of the three short-listed teams invited to submit a detailed conceptual design, the RNL-Haselden group was the only one that offered a net-zero building in its proposal.

The geometry of the windows and shading devices on the RSF's south-facing windows limits heat gain and glare while allowing for effective daylighting. The windows include operable lower vision panels that aid natural ventilation and night flushing. Fixed upper panels have integrated louvers that reflect light toward the ceiling. Light shelves shade the vision panels and direct sunlight through the louvers.

Diagram: Courtesy RNL

 

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Originally published in Architectural Record
Originally published in December 2010

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