Energy Neutrality Proves to be Sponge-Worthy
Event: Mixed Greens lecture:”Zero-Energy Tower, Guangzhou”
Location: New York Academy of Sciences, 05.08.07
Speakers: Roger Frechette, PE, LEED-AP — Director of MEP Engineering, & Russell Gilchrist, RIBA, — Director of Technical Architecture, Skidmore, Owings & Merrill; Carol Willis — Director, Skyscraper Museum (introduction)
Organizer: Skyscraper Museum
Skidmore, Owings & Merrill
The two complementary professions of engineering and architecture gain immeasurably from hearing each other’s languages and concerns. Anatomizing a single building (the Pearl River Tower in Guangzhou, China, scheduled for completion in mid-2009) allows a view into the interlinked processes behind high-performance design. The Skyscraper Museum’s Mixed Greens series concluded with a Skidmore, Owings & Merrill engineer/architect tag-team presentation.
Roger Frechette, PE, LEED AP, began by walking through some of the facts that make sustainable design a priority, particularly the shares of total energy and electricity that buildings consume nationally (40% of the former and 71% of the latter). Overall, because buildings generate as much carbon as transportation and industry combined, Frechette says, “form for the sake of form is no longer good enough.” Borrowing biomimicry principles from Janine Benyus’s work and applying them to new designs, Frechette described four levels of energy processing developed by SOM’s engineers: reduction in consumption; reclamation of lost energy for reuse; passive absorption of natural energy flows such as wind, sun, and water; and generation of power. Sponges, which conduct moisture efficiently, provide habitats for thousands of other species, and channel light through fiber-optic-like microfilaments in their external spicula, offer natural models of structures that can help a building meet the environmental challenges of hot, muggy, heavily-polluted Guangzhou.
To reduce dependency on external power, the Pearl River Tower uses many tricks in the book: 32 different conservation systems, including underfloor air, German-style chilled ceilings, double walls to create ventilation cavities, and non-symmetrically arrayed photovoltaics — a feature that the engineers preferred but the architects had to warm up to (“To achieve optimum performance,” Frechette commented, “you don’t often end up with a symmetric answer”). The building’s orientation defies aerodynamic orthodoxy, turning its wide side to the prevailing southern wind and channeling air into turbines. Since turbine power is a cube function of air velocity, the high winds that typically surround a skyscraper become an energy asset instead of a problem. Placing the turbines on mechanical floors also frees up rentable square footage, as does a compressed floor-to-floor height, allowing five extra stories without sacrificing floor-to-ceiling space.
The Pearl River Tower is a proof-of-concept project for a true energy-neutral building. It’s easily the world’s most efficient tall building, cutting power consumption by 58% over the baseline case and reducing carbon dioxide generation from 20 billion pounds to less than 9 billion. But it only suggests the potential for a building to attain that fourth step and return more power to the city grid than it consumes. In a different site with a less harsh climate (and perhaps more cooperative local utilities), Frechette conjectured, results would be even better. Because the tower is classified as commercial rather than industrial, regulators disallowed a set of highly efficient microturbines that could generate power from either natural gas or methane, along with heat for water — cleanly, more reliably, and more efficiently than Guangzhou’s grid. (The design preserved space for the microturbines anyway, in case the officials change their minds.)
Russell Gilchrist, RIBA, breaking down the various performance benchmarks economically, pointed out that the tower’s multiple economies allow recovery of the up-front sustainable-technology premium in 4.8 years, becoming a net revenue generator for at least 20 years beyond that point. With a financial incentive like that, the challenge to achieve a zero-energy skyscraper is squarely on the table.
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