HONOLULU - Honolulu Seawater Air Conditioning LLC (HSWAC) is currently developing a 25,000-ton seawater air conditioning district cooling system for downtown Honolulu. The system is designed to serve buildings in the downtown core.

As a tropical island state, Hawaii has a year-round, relatively uniform need for air conditioning. Conventional air conditioning systems are energy intensive and represent 35 to 45 percent of energy use in typical office and hotel buildings in Hawaii, said the company. Hawaii also has some of the highest electricity rates and air conditioning costs in the country. And, Hawaii relies on expensive imported fossil fuels for more than 90 percent of its energy needs. At the same time, all islands have some shorelines that have good access to deep, cold seawater used in a seawater air conditioning system.

In operation, a seawater air conditioning system pumps seawater through a supply pipeline to a cooling station on the shore. The intake pipe is located at a depth where the water temperature is 39° to 45°F year-round. Heat exchangers at the cooling station transfer the cold temperatures of the seawater to a fresh water distribution network. The heat exchangers ensure that the seawater and fresh water never mix. The warmed seawater is returned to the sea through a diffuser, while the closed loop, fresh water distribution network, including pumps, provides chilled water to cool the buildings.

Seawater air conditioning is suitable for coastal developments with a large air conditioning demand and reasonable access to deep, cold seawater. Notable areas are southern Kauai, several areas of Oahu, and the southern 60 percent or more of the Big Island, said HSWAC.

A number of studies have been conducted to evaluate the potential of seawater air conditioning in Hawaii, and there is an operating system at the Natural Energy Laboratory of Hawaii Authority (NELHA) at Keahole Point, Hawaii. According to HSWAC, these studies all show that there is significant potential for seawater air conditioning in Hawaii. More recent studies show that combining seawater air conditioning with thermal energy storage and auxiliary chillers increases the cost effectiveness and applicability of such systems.

The Hawaii State Department of Health, Office of Environmental Quality Control (OEQC) has published an initial environmental impact statement preparation notice (EISPN) providing for a 30-day public review and comment period on HSWAC’s downtown Honolulu project. Any comments that are raised during the public review and commenting period of the EISPN will be included and addressed in a subsequent draft environmental impact statement (DEIS).

Publication date: 09/10/2007