Hydrothermal cooling – collectively also known as lake source cooling (LSC) and seawater air conditioning (SWAC) – is the practice of achieving comfort cooling or process cooling from a natural body of water. Readers should understand that water reaches its maximum density at a temperature of approximately 39°F (4°C). Colder, less dense water naturally exists adjacent to this heavy layer.1 Many coastal regions have deep cold water and resources available close to shore.
The predecessor to the US Department of Energy, ERDA, in 1975–77, funded two studies on the "Feasibility of a District Cooling System Using Natural Cold Waters."2 The initial report concluded that the coast of southern Florida, from Fort Lauderdale to Miami Beach, would be the most suitable location in the US to use naturally cold water for comfort cooling. The second report made an actual feasibility study for a Miami Beach seawater district cooling plant situated at Indian Beach Park. The conclusion of the report states that the "payoff of investment costs with energy savings is seen to be in the fifth year of operation." While the plant was never constructed, the site as of 2011 seems to be still available. As of 2010, there were at least four major hydrothermal cooling plants installed around the world. The Purdy's Wharf Complex in Halifax, Nova Scotia, cooled a small office complex.3 Cornell University has followed suit with a lake source cooling system that provides approximately 18,000 to 20,000 tons (63,300 to 70,340 kW) of cooling. For over a decade, the Cornell campus has been cooled with 39°F (4°C) water from the adjacent Lake Cayuga. The previous mechanical chiller plant at Cornell in 1999 was reportedly operating at 0.83 kW/ton (4.24 COP). The LSC plant installed in 2000 is operating at 0.1 kW/ton (35.16 COP) or 86% less electricity.4
According to ocean energy scientist John Craven, hydrothermal cooling is 90% more efficient than electric air conditioning referring to the SWAC system installed at the Intercontinental Resort and Spa in Bora Bora of the Leeward Islands of French Polynesia.5
Taking the current lead in hydrothermal cooling, the Enwave District Cooling project in Toronto, Canada, provides approximately 59,000 tons (207,500 kW) of cooling from 39°F (4°C) water from the 200-meter-deep water of neighboring Lake Ontario.6 The project's final cost was approximately $128 million dollars but one of the key return-on-investment strategies was to dual purpose the water, not only for cooling but also for pure drinking water. The Toronto Enwave Lake Source District Cooling project connected three sections of 2-kilometer-long pipe and floated the 6,000 meters of piping onto Lake Ontario. To submerge the piping, they employed a controlled submergence technique developed by Joe Van Rysin and his team at Makai Engineering, Hawaii. In earthquake or hurricane prone areas another technique to access and discharge the water with less risk is to use directional drilling and/or tunnel boring machines known as drilled hydrothermal energy.7
1. "Properties of water." Density of saltwater and ice. Wikipedia. 2011.
2. Hirshman J. and R. Kirklin. 1977. Feasibility Of A District Cooling System Using Natural Cold Waters Final Report – Phase II: Site Specific Study & Preliminary Design of a Miami Beach Seawater Cooling District / Phase III: Preliminary assessment of the Fresh Water Resource for the District Cooling of Buildings. Community Systems Branch US Energy Research & Development Administration. Washington, D.C.
3. "Seawater Cooling System for Buildings." Caddet Energy Efficiency. International Energy Agency Organization for Economic Co-operation and Development, Nov. 1992.
4. "Cornell University Facilities Services Energy and Sustainability." Lake Source Cooling Project at Cornell: Cooling Production Home 2011.
5. "InterContinental Bora Bora - Deep Sea Water Air Conditioning." YouTube. 27 Feb. 2007.
6. Enwave Energy Corporation. Enwave. Web. 13 June 2010.
7. Jagusztyn, Tadeusz F., Reny, Marie (2010) "Natural Cold Water District Cooling Plants Enabled by Directional Drilling – Road to Climate Friendly Chillers" UNEP – ASHRAE Conference Sept 2010 Cairo Egypt.