First in a warm-weather city

Christopher Pala




 
Honolulu is set to become the first warm-weather city in the world to have its heart cooled by seawater pumped from the deep, cutting the power bills of building owners and reducing greenhouse emissions, according to an environmental impact statement published this fall.
  Until mass tourism began sprouting skyscrapers from Waikiki to Pearl Harbor, Honolulu was a city of widely spread-out buildings shaded by giant monkeypod trees naturally cooled by the strong trade winds that prevail 2000 kilometres north of the equator.
  But the forest of concrete structures, which not only trap heat but emit it through air-conditioning, have turned the city center into a heat island and have become a drain on the state’s over-extended power-generation system, which uses oil for more than 90 percent of its output, more than any other state.
  The deepwater technology is already used in Toronto and Stockholm to balance temperatures inside large buildings, notably to cool areas with computer servers and telephone exchanges during the summer months.
  But, says William M. Mahlum, president of Honolulu Seawater Air Conditioning LLC, which is undertaking the $240-million project, “This is the first time it will be used to cool a warm-weather city center.”
  The company, owned by investors in Hawaii, Sweden and Minnesota, is managed by Renewable Energy Innovations, a unit of Ever-Green Energy Co. of St. Paul, Minn., which runs that city’s heating and cooling systems.
 
  Ground-breaking
  Ground-breaking is expected next summer and the first 40 buildings are expected to come online in late 2012. Another five will be added the following year.
  Once the system is up and running, predicts Mahlum, a tall, grandfatherly Minnesotan who’s been working for Ever-Green for 30 years, it should inspire tropical coastal cities around the world to harness the technology.
  He says the technology could cool Miami, Acapulco and a lot of other coastal cities.
  “All you need is a steep enough coastal gradient and concentrated demand,” he says.
  The system will save clients about 20% in cooling costs, the company says; and by reducing power usage by 77 million kWh/year, or 75% of the present consumption, it will cut carbon dioxide emissions by 84,000 tons a year, nitrogen oxides by 169 tons and sulfur oxides by 165 tons.
  It will also reduce the use of toxic refrigerants and save 260 million gallons per year of drinking water.
  And finally, it will end the dumping into the city sewers of 84 million gallons per year of used cooling tower water containing such toxic chemicals as phosphoric and sulfuric acids, according to Ingvar Larsson, Honolulu Seawater’s Vice President of Engineering.
  The seawater cooling system, says Mahlum, the company president, will reduce its customers’ cost for air conditioning from the start. Over time the savings will grow if the price of oil increases.
  “Most green energy projects focus on generating clean electrons,” says Jeff Mikulina, head of the Blue Planet Foundation, whose goal is to promote clean energy.
  “The beauty of this one is that it avoid electrons altogether by tapping into a vast local resource.”
  Here’s how it works: a five-foot-wide pipe extends four miles out to sea to a depth of 1,700 feet, brings in 44,000 gallons per minute of water at 45 degrees (F).
  Once ashore, the water goes through a conventionally powered chiller that brings it down to exactly 44 decrees F, then loops through a heat exchanger with a closed-circuit freshwater system and is released back into the sea at a depth of 200 feet at 56 degrees—the natural temperature at that depth.
  Meanwhile, the cooled freshwater makes its way to the buildings’ air conditioning units and cools the air propelled by fans over the coils. This allows the building to turn off the energy-hungry compressor that previously chilled the coil and the cooling towers.
  Like most tropical or sub-tropical cities, Hawaii sees a surge of power demand in the middle of the day driven by air conditioning, so it saves not only power, but premium power, notes Mikulina.
 
  Relieve strain
  “This project will help relieve some strain on the power grid.”
  Worried that it warms up the ocean? Not at all, says Larsson, the vice-president for engineering.
  “If you look at the heat we emit in both the ocean and atmosphere, it’s 40 percent less than a conventional air conditioning system, and of course by cutting greenhouse gases, we slow global warming.”
  Peter Rosegg, a Hawaii Electric Company spokesman, has nothing but praise for the project. “By reducing our load, it allows to increase our reliability to other customers,” he says.
  The system will reduce electricity generation in Hawaii by only one percent—one year’s worth of growth in demand.
  But Rosegg says, “One percent may not seem like much, but this is an important one percent because the downtown area has banks and medical centers that require very reliable power.
  “They can’t afford dips and curls, and seawater cooling is much more even than, say, wind and power, which go up and down a lot.”
  The next logical step would be neighboring Waikiki, where over a third of the power use is taken up by air conditioning.
  Honolulu Seawater Air Conditioning officials say that once the project is finished, they expect to create another unit in Waikiki, with its own pipe into the ocean. This would take another five years.
  It’s not surprising this first came about in Hawaii. It was on the Big Island that in 1974, the Natural Energy Laboratory of Hawaii Authority did the first US tests of Ocean Thermal Energy Conversion (OTEC) to see if temperature differences between the deep and the surface could be turned into electricity economically.
  The answer was: not yet, but as a sideline the laboratory created the world’s first air conditioning system using cold seawater pumped in from the deep. The system is still working.