The Blue Revolution
Part One
Many great cities around the world are located near ocean shores or deep lakes. The cities of Toronto, Stockholm and Honolulu, and the Cornell University campus are showing the world what can be done using cold deep water to power the cooling of large buildings, providing a large saving in energy and cutting down on carbon emissions and pollution from energy generating plants.
Toronto initiated the cooling system in 2004 by the company Enwave District Energy Ltd. A five-kilometre long pipe draws cold (4 C) water from the depths (83 metres down) of Lake Ontario to Toronto Island (just offshore of Toronto) where the water is filtered and treated with chlorine as it is delivered to taps in homes and businesses. After treatment, the very cold water flows to a city plant that employs a heat exchanger to transfer heat from the water to cool a closed cooling water loop that circulates to the distribution network, where more heat exchangers cool the water circulating through the air conditioning systems in the office towers. The system will meet up to about 40 percent of the city's cooling needs. Toronto, like most Midwestern Cities, has very hot and humid summers, which put a huge demand on the electrical supply, so that the lake cooling system brings very welcome relief and protection against electrical "brown out". Cooling is provided for office towers, sports and entertainment facilities and waterfront developments. Currently, government buildings including the Ontario legislative complex are being modified for lake-water cooling.
Cornell University draws cold water from a nearby deep lake, Lake Cayuga. The water is pumped to a heat exchanger at the shore where the campus and a school share a cooling loop, and the warm water from the buildings flows down to push cool water up to the campus. The system is both elegant and cost effective.
Stockholm is employing cold deep-sea water to cool buildings. In central Stockholm, the cooling plant comprises four heat pumps that obtain their energy from seawater.
The plant has two seawater inlets, one at the surface and the other at a depth of 20 meters. Cooling is produced by cold water drawn through the inlet to a heat pump and then passes to heat exchangers that cool the water used to cool buildings in the central district. The heat exchangers are made of titanium to withstand the corrosive seawater. The surface inlet delivers water to the heat pump, which produces heating energy for delivery to the heating network.
Honolulu has been investigating alternative uses of seawater in cooling. The results were published as the proceedings of a 2003 workshop. One system draws very cool water from the offshore depths and delivering it to heat exchangers to cool hotels and other large buildings. The other system generates electrical energy using the stored energy of sun-warmed water to energize the evaporation of ammonia to drive turbines to create electricity. [A Minnesota company has just been awarded a $150 million contract in Hawaii to install a deep ocean cooling system drawing cold water from 4 miles offshore at a depth of 1600 ft. -- Ed.]
In 1986, the Natural Energy Laboratory of Hawaii Authority, Keahole Point, Hawaii began the successful utilization of seawater air-conditioning in their main laboratory building. Deep-water pipelines were already installed to provide cold, nutrient rich, seawater for research purposes in alternate energy and aquaculture. As a cold water supply was already incorporated into the infrastructure, they decided to use it for cooling. Today, seawater air-conditioning has been expanded to a new administration building and a second laboratory. Installations for deep water cooling have been proposed for other locations in Hawaii including Kahoolawe, Kona Airport and the new town of Kapolei, Oahu. Currently, seawater cooling systems are under construction in Tahiti, Curacao, Korea, Malta, the Cape Verde Islands, Haiti and Mauritius. The Guam Power Authority put together an extensive report on the project at Tumon Bay Environmental impact study.
A territory-wide system for cool water air-conditioning is planned for Hong Kong, the proposed project included consideration of environmental impact. China undertook a study of the impact of proposed Chinese coastal municipal air conditioning using deep ocean water. The study dealt with the issue of warming deep water on the intensity of El Nino effects, and concluded that the impact of deep water-cooling to air-condition coastal cities was negligible at a coarse-grained level, but there could be local hotspots in temperature changes.
Deep-water air-conditioning could be considered for other major cities located near the ocean or near deep lakes, as it has the advantages of low cost, great savings on energy and on air-conditioning chemicals. From the systems described above, deep-water air-conditioning may be suitable for both large and mid-size to small communities or for universities, hospitals or hotel resorts. [I have no doubt that Canada, with more freshwater and ocean shoreline than most countries on earth, will with relative ease be tapping into this enormous resource. However, as with anything we humans do to improve our indoor environment, there is often a catastrophic reaction in the outdoor environment. -- Ed.]
Watch for Part Two of the Blue Revoluton to find out.
