The developers of a project that will use cold ocean water to air-condition office buildings in downtown Honolulu have signed a long-term lease for a pumping station site, clearing the way for construction of the system to begin early next year.

Honolulu Seawater Air Conditioning LLC signed a 55-year lease with Kamehameha Schools for a 30,000-square-foot parcel behind the Gold Bond Building in Kakaako that will be home to a pumping station and heat exchanger that will be the heart of the system, the company said Friday.

“We’re very pleased to have that in place, and we’re ready to go,” said Bill Mahlum, president and chief executive officer of the company. He said Honolulu Seawater is getting all the necessary permits as well as finalizing financing for the $266 million project.

The company, which has postponed the project’s start date several times, now says it plans to break ground early next year. Service to customers is projected to begin sometime in 2013, according to the company.

The system will replace the need for chillers used in commercial air-conditioning systems and cut electricity costs by up to 75 percent, the company said. Similar costs savings were achieved at sea water air-conditioning projects in Canada and Sweden, said Anders Rydaker, the company’s chief operating officer.

Plans call for pumping water through an intake pipe extending four miles offshore to a depth of 1,600 to 1,800 feet. The 45-degree water will be run through a heat exchanger that will chill a closed loop of fresh water circulating in a network of pipes through downtown buildings.

The plan has been endorsed by Hawaiian Electric Co. officials, who said it will save more electricity than the combined output of all the solar photovoltaic systems in the state.

Part of the state’s effort to reduce its dependence in imported oil for energy generation “will be to find every way we can to be smarter about our use of electricity, and sea-water air is one of those,” said Robbie Alm, HECO executive vice president.

Alm said motorists and pedestrians in the downtown area will be inconvenienced when construction crews begin work on the network of underground cold-water pipes.

“This an immense project in terms of the offset of power. So if it causes us a little bit of disruption … then we should just look at it and say, ‘OK, that’s oil disappearing to some extent from our lives,'” Alm said.

The project will be paid for with a mix of equity and debt financing.

Honolulu Seawater already has raised $16.8 million in equity to fund the project’s operations, Mahlum said. In addition, the company has three investment funds bidding to supply an additional $36 million in equity.

The company plans to float $145 million in state special-purpose revenue bonds that are exempt from state and federal taxes. The balance of the financing will be paid for with bank loans or taxable bonds, Mahlum said. Goldman Sachs is assisting with sales of the bonds, he said.

The project is expected to generate more than $200 million in construction spending and create about 900 construction jobs, the company said.