By Jan TenBruggencate
Advertiser Columnist

Air conditioners are comparatively cheap to install, but they're power hogs, typically using as much as 40 percent of the electricity needed to run large buildings.

Hawai'i researchers say there's a much cheaper way of cooling buildings near the ocean, although the disadvantage is that it's expensive to install.

The proposed system uses the cool water of the deep ocean, said David Rezachek, alternate-energy specialist with the state Department of Business, Economic Development and Tourism's energy division.

A pipeline into the deep ocean could bring up cold water that could cool buildings for as little as 10 percent of the energy cost of traditional air conditioning, he said. The cold seawater would be pumped ashore to a heat exchanger, where it would cool piped fresh water. The fresh water could then be pumped to buildings along the shoreline and used to cool indoor air.

This isn't untried technology. Cornell University is air-conditioned with water pumped from deep in adjacent Lake Cayuga, through a pipeline that was designed by the Hawai'i firm Makai Ocean Engineering. The firm is conducting studies for similar systems worldwide.

Water at 1,600 feet depth off the south coast of O'ahu is 45 degrees Fahrenheit. At 3,300 feet, it's 39 degrees. A study on developing seawater air conditioning looked at sites around the state, and found that in many places, when the cost of installation is included and amortized, a seawater district cooling system is 18 percent to 58 percent cheaper than conventional cooling.

"Savings of these magnitudes could justify a significant reduction in cooling costs ... while still providing developers with a good return on investment," said the study's executive summary. Such systems also could significantly reduce the state's electricity demands, and thus cut oil imports.

State officials are sponsoring an "Innovative Energy Systems Workshop" March 19 and 20 at the Pagoda Hotel to review the findings of the seawater air-conditioning study. For information about the workshop, call Rezachek at 587-3814 or e-mail drezache@dbedt.hawaii.gov.

The session will include discussions of the Kalina heat engine, a design that uses heat to produce mechanical power. For example, Rezachek said, a Kalina cycle engine could use waste heat from generators or other heat-producing equipment to operate the pumps that run a seawater air-conditioning system.

The Kalina cycle engine is 10 percent more efficient than similar heat engines, according to the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy. The technology is being used in some geothermal power plants.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Reach him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.