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Hawaii's Deep Blue Solution to A/C Woes

Hawaii sunset

The design is complex, the island logic simple: Find a cheaper way to cool tropical buildings and you can spend less on imported oil. All that money saved on overhead means—Aloha!—more clam shells for everyone to dump back into the economy.

That's the $200 million gamble going on in Honolulu right now, where Honolulu Seawater Air Conditioning just got the green-light to build one of the most elaborate "ocean thermal" projects in the country. By 2012, a complex network of pipes extending five miles off shore and 1,800 feet deep will begin pumping frigid deep sea water to help chill downtown office buildings.

Though variations of the concept have been tried at Cornell University and in Toronto and Sweden (the National Energy Laboratory of Hawaii Authority uses a smaller version of the technology to save about $4,000 a month), this is a big deal for Honolulu, where the confluence of steep plane tickets and a steeper cost of living means 10.5% fewer people visited the state as a whole in 2008. The drop-off cost hotels a whopping $156 million and merchants millions more in lost surfboard rentals and stagnant puka-shell necklace sales. Things have rebounded a bit, visitors are reportedly spending far less freely (PDF file). Also, Hawaii imports more than 90% of their mostly oil-based energy needs from other mainlands, racking up the highest energy bills of any state in the union.

The deep water cooling process is far more simple than it sounds. As you can see from the diagram below, Poseidon's most abundant resource won't actually be pumped into buildings themselves; the 40-degree briny water will be transferred to a cooling station where its energy will help cool a small batch of fresh water, leaving less chance that a sprung gasket would flood cubicle farms like a beached Titanic. Of course any leak in the system would be a heck of a lot easier to mop up than, say, the Exxon Valdez.

Hawaii water

The payout: An estimated 75% reduction in traditional energy consumption saving 147 million barrels of oil and 84,000 tons of carbon dioxide, annually. Over time, the millions potentially saved on utility bills can be injected back into the vacation economy.

Of course, to ensure ends meet, the Honolulu projects seems to have been purposely under-built. HSAC President Bill Mahlum estimates his pipes pump about 28,000 tons, enough to cool about 40 buildings, depending on their size, but Honolulu's shoreline actually has capacity for more like 45,000 tons of usage, so those who don't sign up early will likely miss out.

Sadly some condo rental owners who tried to develop their own quick fix in recent years—newer construction residential buildings with individual air-conditioning systems that can be shut down when the tourist season slumps—won't have the centralized infrastructure to opt in. And continuing to rent those places might soon get harder if competing resorts take advantage of the money-saving deep water tech. Mahlum has already expressed interest in running another pipeline just a few miles away to the luxe resort mecca Waikiki.

[Photo by Chris Chappelear]