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Cooling Downtown with Seawater in Honolulu

Bill DiBenedetto | Friday December 11th, 2009 | 6 Comments

Honoes-2009-033364_0001Within the next couple of years Honolulu will become the first warm-climate city to use frigid deep-sea water to cool part of its downtown core.

Honolulu Seawater Air Conditioning, a limited liability company created specifically to develop the $240 million project, says its technology will cut the city’s air conditioning electricity usage by up to 75 percent, while also drastically reducing carbon emissions and the use of refrigerants.

HSWAC plans to cool more than one-half of the Hawaiian city’s downtown skyscrapers by 2012, using ocean water pumped through a pipeline.

The five-foot pipeline 1700 feet below the surface and four miles out to sea will suck up tens of thousands of gallons of really cold water and discharge it through air-conditioning units around the city. The warmed water will then be returned to the ocean at a level and temperature that will not harm aquatic life.

This technology is already used in Toronto and Stockholm to balance temperatures inside large buildings and to cool areas with computer servers and telephone exchanges during the summer months. The Stockholm system, Europe’s largest seawater AC project, handles approximately 80,000 tons of air conditioning load and is still expanding.

“This is the first time it will be used to cool a warm-weather city center,” says HSAC President William M. Mahlum.

The company is owned by investors in Hawaii, Sweden, and Minnesota and is managed by Renewable Energy Innovations, a unit of Ever-Green Energy Co. of St. Paul, MN. Ever-Green Energy in turn is a for-profit affiliate of District Energy St. Paul, a non-profit heating utility, and District Cooling St. Paul, a non-profit cooling utility.

Groundbreaking in Honolulu is planned for next summer, and the first 40 buildings are expected to come online in late 2012. Another five will be added the following year to reach a maximum capacity of 28,000 tons.

Once the system is running, predicts Mahlum, it should inspire tropical coastal cities around the world to harness the technology. “We know this could work in Miami, Acapulco, and a lot of other coastal cities,” he said, quoted in a recent American Chemical Society article. “All you need is a steep enough coastal gradient and concentrated demand.”

Mahlum said in the article that the system will save clients about 20 percent in cooling costs. It will reduce power use by 77 million kilowatt hours per year, or 75 percent, thus cutting CO2 emissions by 84,000 tons, NOX by 169 tons, and sulfur oxides by 165 tons per year. It will also reduce the use of refrigerants such as HCFC-22, HCFC-123, and CFC-11/500.

It has a steep price tag, a complicated ownership structure and curious Hawaii-Minnesota-Europe connections, but hey, it’s the new energy economy, right?

Let the waters flow and turn off those compressors.


▼▼▼      6 Comments     ▼▼▼

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  • nickaster

    I love this kind of novel technology use, but in the case of Honolulu it seems like over-design to me. Do people really need air conditioning in Hawaii? The temperature is almost always perfect… it c ould be a little warm on some days, so that's when you open a window. If downtown buildings were simply designed with operable windows instead of being impermeable boxes, you wouldn't need to spend all the money on a system like this, or AC at all!

  • Brian

    I'm no scientist. I've read that below a certain depth, around 3,500 feet I think, calcium carbonate, CaCO3, the stuff of shells and diatom skeletons, dissociates to Ca++ and H2CO3 due to water pressure and temperature. I’m not sure, but I think if you pump that water to the surface, the H2CO3 turns into water and CO2. If it does, some of the deep water schemes may have to rethink. Any ideas?

  • jenboynton

    I think it's not so much the heat as the humidity- with open air all the time there are big mold considerations. But operable windows are a no-brainer in pretty much any climate.

  • lauriesanford

    In response to Nick's comment, having high rises, that block the natural cooling trade winds in Hawaii and having buildings in which the windows don't open are both problems. However that is the configuration of the downtown of Honolulu right now. I have no idea what it would cost to redo most of the windows in the city and the chances of flattening the buildings seems highly unlikely. I also think though, that whether or not a place feels “hot” or “cold” is up to the residents of that place to a large degree and while air conditioning is much less prevalent in Hawaii than in other warm places, it still exists. Jen is right that humidity and it's resultant mold is a serious comfort and health problem that is emerging into awareness in Hawaii. Additionally so is VOG, naturally occuring from the ongoing volcanic eruptions. Sept./Oct. tend to be times when 'Kona winds' (warm westerly winds) prevail and Hawaii is naturally warmer. I love this idea! Using the cool ocean waters that are right off the downtown area to help reduce air conditioning and potentially other electricity use seems like a great idea! I don't know about the science that a previous commentator mentioned that might bring co2 to the surface in this process. I would love to hear more about that! But Hawaii is one place that ought to be able to become sustainably self-sufficient in terms of energy use and food production with it's wealth of wind, sun, ocean, It's relatively small size and it's culture of inter-dependancy and probably the best weather and climate on earth!

  • preshy.

    75%..?wow..i'll believe it when i see it..

  • preshy.

    75%..?wow..i'll believe it when i see it..