Deep Cold Seawater, An Asset To Desalination
VanRyzin, J.C., 1998. The Next Breakthrough in Seawater Desalination, Curacao, Netherlands Antilles

One of the major costs of desalination is energy. Several desalination projects are currently underway that are focusing on the use of the temperature differential between deep cold seawater (at 4° to 6° C) and ambient surface heat sources to power the desalination process, and thus reduce conventional energy requirements. This paper briefly describes two of these processes currently under development, a Thermocline Driven Desalination (TDD) system that uses multistage flash evaporators and a freezing process using clathrates that form in the cold seawater. Both of these processes are a form of Ocean Thermal Energy Conversion (OTEC).

One of the major components in all OTEC processes is the reliable and economical installation of the deep cold seawater pipelines supplying the plants. This paper describes existing pipelines and the methods used to design and install these pipelines in the State of Hawaii. Hawaii has been a center for OTEC development in the United States over the past twenty years and has gained some experience in cold water pipe technology. This paper is a review of that experience, illustrating that deep cold water pipelines can be installed reliably using a variety of techniques.

Deep cold seawater is an extremely valuable renewable energy resource. Considerable research has been underway in the conversion of this resource to electricity, air-conditioning and fresh water. Today, providing air conditioning and potable water via deep cold seawater is economically viable for communities situated close to this valuable resource.

Cold Water Pipe Technology: Hawaii Experience
VanRyzin, J.C., 1996. US Navy-Industry Symposium on Ocean Thermal Energy Conversion, Kailua-Kona, Hawaii.

Ocean Thermal Energy Conversion (OTEC) requires huge quantities of deep cold seawater and warm surface water to operate. The fabrication and installation of deep water pipelines to provide this water represents the single most expensive portion of any OTEC plant and the highest risk during construction. In spite of these costs and risks, and partly because of these costs and risks, it is the least demonstrated major component of a large OTEC plant.

Hawaii has been a center for OTEC development in the United States over the past fifteen years and has gained some experience in cold water pipe technology. This paper is a review of that experience and the lessons learned from installing a wide variety of small (by OTEC standards) diameter deep water pipelines. The problems learned and successes gained in small diameter pipelines have applications to larger pipes needed in the future of OTEC.

Air Conditioning With Deep Seawater: A  Cost Effective Alternative For West Beach, Oahu, Hawaii
Leraand, T.K., and J.C. VanRyzin, 1994.

Deep cold seawater can be a practical and economically viable source of cooling in a centralized air conditioning system. A seawater air conditioning system (SWACS) uses cold sea water from approximately 2000’ depth to cool (via a heat exchanger) a centralized fresh chilled water distribution loop serving multiple buildings. At ideal coastal sites, SWACS power savings can approach 80% compared to conventional chillers. This paper summarizes the technical and economic feasibility of such a centralized air conditioning system at West Beach, Oahu, Hawaii. West Beach is an ongoing development of resort hotels with good access to deep cold seawater. Centralized seawater air conditioning is a technically feasible and unsophisticated alternate energy concept that has the potential of significant impact in Hawaii and other similar regions. The installation of large systems at selected locations is economically attractive today.

Air Conditioning With Deep Seawater: A Reliable, Cost Effective Technology
VanRyzin, J.C., and T.K. Leraand, 1991. Proceeding of IEEE Oceans’91 Conference, Honolulu, Hawaii.

Deep, cold seawater has long been recognized as a valuable energy resource, and early studies in the 1970's, motivated by the energy crisis, identified its advantages for coastal air conditioning.1,2  Air conditioning with seawater uses only a small fraction of the electrical power required for conventional air conditioning.  At the time of these studies, however, the cost of the seawater air conditioning system was uncertain because pipelines had not been built to the water depths required and heat exchangers had significant unknowns relative to corrosion, fouling and costs.  This has now changed.  Over the last decade, research on Ocean Thermal Energy Conversion (OTEC) has brought the development of reliable, moderately sized pipelines suitable for cold water air conditioning and the development of low cost aluminum heat exchangers compatible with deep, cold seawater.  Air conditioning with seawater for some areas is now a reliable, cost-effective technology. 

This paper summarizes the operation of an air conditioning system using deep, cold seawater and identifies the primary conditions under which a system can be cost effective.  The primary factors impacting the economic success of such a system is the size of the air conditioning load, the accessibility to deep cold water, the percent utilization of the air conditioning system and the local cost of electricity.  This paper provides data and graphs that are suitable for an initial assessment of the economic pay back period based on these site-specific conditions. 

Steep Slope Seawater Supply Pipeline
Lewis, L.F., VanRyzin, J.C., and L.A. Vega, 1988.   Proceedings, American Society of Civil Engineers, 21st Conference on Coastal Engineering, Costa del Sol-Malaga, Spain.

The State of Hawaii's Ocean Science and Technology  (HOST) Park, the U.S. Department of Energy (DOE) and the Pacific International Center for High Technology Research (PICHTR) sponsored the construction and installation of an expanded seawater supply system at the Natural Energy Laboratory of Hawaii (NELH).  This effort included the installation of a 1.0m diameter high density polyethylene pipe capable of delivering 840 l/s of cold seawater, representing the longest (2,060m) large diameter pipe traversing the steepest slope ever spanned.  Acceptance testing of the system was completed in June 1988 and the design service life is 10 years.

The HOST-Seacoast Test Facility (OTEC) Project in Hawaii, Planning, Design and Construction
Vuillemot, F.L., Van Ryzin, J.C. and A.M. Resnick, 1988.  Presented at the Marine Technology Society Pacific Congress on Marine Science and Technology (PACON '88), Honolulu, Hawaii.

The Hawaii Ocean Science and Technology-Seacoast Test Facility (Ocean Thermal Energy Conversion) project is nearing completion at Keahole Point on the Island of Hawaii. The project taps both shallow (warm) and deep (cold) ocean waters for use in open-cycle OTEC experiments and in commercial mariculture. The pumping system will provide a total of 22,900 gpm of ocean water to the Natural Energy Laboratory of Hawaii for distribution to the onshore OTEC experiments and the HOST Park mariculture facilities.

The shoreline pumping station is buried below grade for protection against storm wave attack and tsunamis.  The intake and distribution pipes and the pumps are made of inert materials to keep harmful metallic ions out of the water destined for mariculture use.

The deep offshore cold water pipe (one meter diameter) is 2000 meters long and extends from the shoreline pumping station to a depth of 700 meters, using an inverted catenary span. The irregular bottom conditions and strong currents required an unusually complex design and deployment plan for the high density polyethylene pipe.