Deep water source cooling (DWSC) or deep water air cooling is a form of
air cooling for process and comfort space cooling which uses a large body of naturally cold water as a
heat sink
A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is thermal management (electronics), ...
. It uses water at 4 to 10 degrees Celsius drawn from deep areas within lakes, oceans,
aquifer
An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...
s or rivers, which is pumped through the one side of a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
. On the other side of the heat exchanger, cooled water is produced.
Basic concept
Water is most dense at at standard atmospheric pressure (not true for seawater). Thus as water cools below 3.98 °C it increases in density and will settle below. As the temperature climbs above 3.98 °C, water density also decreases and causes the water to rise, which is why lakes are warmer on the surface during the summer. The combination of these two effects means that the bottom of most deep bodies of water located well away from the equatorial regions is at a constant 3.98 °C.
Air conditioners are
heat pump
A heat pump is a device that uses electricity to transfer heat from a colder place to a warmer place. Specifically, the heat pump transfers thermal energy using a heat pump and refrigeration cycle, cooling the cool space and warming the warm s ...
s. During the summer, when outside air temperatures are higher than the temperature inside a building, air conditioners use electricity to transfer heat from the cooler interior of the building to the warmer exterior ambient. This process uses electrical energy.
Unlike residential air conditioners, most modern commercial
air conditioning
Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...
systems do not transfer heat directly into the exterior air. The thermodynamic efficiency of the overall system can be improved by utilizing
evaporative cooling
An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning sy ...
, where the temperature of the cooling water is lowered close to the
wet-bulb temperature by evaporation in a
cooling tower
A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream, to a lower temperature. Cooling towers may either use the evaporation of water to remove heat and cool the ...
. This cooled water then acts
as the heat sink for the heat pump.
Deep lake water cooling uses cold water pumped from the bottom of a lake as a
heat sink
A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is thermal management (electronics), ...
for
climate control systems. Because heat pump efficiency improves as the heat sink gets colder, deep lake water cooling can reduce the electrical demands of large cooling systems where it is available. It is similar in concept to modern
geothermal sinks, but generally simpler to construct given a suitable water source.
Deep lake water cooling allows higher thermodynamic efficiency by using cold deep lake water, which is colder than the ambient
wet bulb temperature. The higher efficiency results in less electricity used. For many buildings, the lake water is sufficiently cold that the refrigeration portion of the air conditioning systems can be shut down during some environmental conditions and the building interior heat can be transferred directly to the lake water heat sink. This is referred to as "free cooling", but is not actually free, since pumps and fans run to circulate the lake water and building air.
One added attraction of deep lake water cooling is that it saves energy during peak load times, such as summer afternoons, when a sizable amount of the total electrical grid load is air conditioning.
Advantages
Deep water source cooling is very energy efficient, requiring only 1/10 of the average energy required by conventional cooler systems.
Consequently, its running costs can also be expected to be much lower.
The energy source is very local and fully renewable, provided that the water and heat rejected into the environment (often the same lake or a nearby river) does not disturb the natural cycles. It does not use any
ozone depleting refrigerant
A refrigerant is a working fluid used in the cooling, heating, or reverse cooling/heating cycles of air conditioning systems and heat pumps, where they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are ...
.
Depending on the building's cooling demand, and local weather, deep water source cooling can often satisfy a complete portion of a building's cooling demand, eradicating a building's reliance on mechanical refrigeration provided through a
chiller. This not only reduces the building's electrical demand (or steam demand for applications using
absorption refrigeration), but also curtails dependency on evaporative
cooling towers which can oftentimes harbor the fatal bacterium
Legionella pneumophila
''Legionella pneumophila'', the primary causative agent for Legionnaires' disease, Legionnaire's disease, is an Aerobic organism, aerobic, pleomorphic, Flagellum, flagellated, non-spore-forming, Gram-negative bacteria, Gram-negative bacterium. ' ...
. However, building operators must adhere to, and practice correct disinfection procedures before restarting any cooling towers which remained dormant during cooler days when deep water source cooling was able to meet the building's cooling demand.
Depending on the needs and on the water temperature, couple heating and cooling can be considered. For example, heat could first be extracted from the water (making it colder); and, secondly, that same water could cycle to a refrigerating unit to be used for even more effective cold production.
Lake temperature is rarely significantly changed by these systems. In Europe, lake-based heating and cooling could save 0.8 TWh per year, and is most promising in Italy, Germany, Turkey and Switzerland.
Disadvantages
Deep water source cooling requires a large and deep water quantity in the surroundings. To obtain water in the range, a depth of is generally required, depending on the local conditions.
The set-up of a system is expensive and labour-intensive. The system also requires a great amount of source material for its construction and placement.
Although deep water source cooling is referred to as "free cooling" in some literature, a considerable amount of energy (typically electrical) is expended to operate pumps with a sufficient head to overcome frictional, and minor losses in distribution piping, and any heat exchangers.
One study found lakes in Europe would only economically serve about 17% of the cooling demand and 7% of combined heating and cooling demand in nearby areas.
First major system in the United States
Cornell University
Cornell University is a Private university, private Ivy League research university based in Ithaca, New York, United States. The university was co-founded by American philanthropist Ezra Cornell and historian and educator Andrew Dickson W ...
's Lake Source Cooling System uses
Cayuga Lake as a heat sink to operate the central chilled water system for its campus and to also provide cooling to the
Ithaca City School District. The system has operated since the summer of 2000 and was built at a cost of $55–60 million. It cools a 14,500
ton (51
megawatt
The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
) load. The intake pipe of the system is long and has a pipe diameter of , installed at a depth of , allowing access to water temperatures between . The water is returned to the lake through a outfall pipe, long. The pipe selected for the project was Sclairpipe, made from high density polypropylene (HDPE). Estimated savings is an 80% reduction in fossil fuel previously required to operate a conventional electric cooling system.
First system in Canada
Since August 2004, a deep lake water cooling system has been operated by the
Enwave Energy Corporation in
Toronto
Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...
,
Ontario
Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
. It draws water from
Lake Ontario
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York (state), New York. The Canada–United Sta ...
through tubes extending into the lake, reaching to a depth of where the water is maintained at a constant 4 °C, its temperature protected by a layer of water above it, called a thermocline. The deep lake water cooling system is part of an integrated
district cooling system that covers Toronto's financial district, and has a cooling
power of 59,000 tons (207 MW). The system currently has enough capacity to cool of office space.
The installed deep lake cooling water intake line was in diameter, long and installed at a depth of allowing access to water temperatures of between 3-5 C (37-41 F). The selected pipe was Sclairpipe, made from high density polyethylene (HDPE) resin.
Water drawn from the depths of Lake Ontario is not circulated directly through terminal air-conditioning units within buildings. Instead, water from the Lake is circulated through a set of closed-loop
heat exchangers in order to allow for a net transfer of thermal energy from heat transfer fluid returning from buildings to the Lake water. Chilled water within the buildings is part of a closed-loop district cooling system, pumped from a centralized location where the heat-exchangers are installed, back to the buildings where it can absorb heat from fan coil units installed to provide latent, and sensible space cooling.
The cold water drawn from Lake Ontario's deep layer in the Enwave system is not returned directly to the lake once it has been run through the heat exchange system. Instead, water is pumped to the city's water filtration plant for treatment and distribution to residential and commercial users.
Sea water air conditioning

This version is also known as ocean water cooling. The
InterContinental Resort and Thalasso-Spa on the island of
Bora Bora
Bora Bora (French language, French: ''Bora-Bora''; Tahitian language, Tahitian: ''Pora Pora'') is an island group in the Leeward Islands (Society Islands), Leeward Islands in the Pacific Ocean, South Pacific. The Leeward Islands comprise the we ...
uses a seawater air conditioning (SWAC) system to air condition its buildings. The system accomplishes this by passing cold seawater through a heat exchanger where it cools freshwater in a closed loop system. This cool freshwater is then pumped to buildings and is used for cooling directlyno conversion to electricity takes place. Similar systems are also in place in
The Excelsior hotel
and
The Hong Kong and Shanghai Banking Corporation main building in
Hong Kong
Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...
, and at the
Natural Energy Laboratory of Hawaii Authority.
Salt water air conditioning systems have been used in Sydney's
Circular Quay
Circular Quay is a harbour, former working port and now international passenger shipping terminal, public piazza and tourism precinct, heritage area, and transport node located in Sydney, New South Wales, Australia, on the northern edge of the ...
and prominent buildings within the harbour since the rise of commercial air conditioning systems in the 1960s. These include the heritage-listed AMP 'Palm Cove' Building (constructed 1962) and the
Sydney Opera House
The Sydney Opera House is a multi-venue Performing arts center, performing arts centre in Sydney, New South Wales, Australia. Located on the foreshore of Sydney Harbour, it is widely regarded as one of the world's most famous and distinctive b ...
.
The
InterContinental Resort is the largest seawater air conditioning system to date, though there are several other, larger systems being planned. Honolulu Seawater Air Conditioning was a project intended to use seawater air conditioning to deliver renewable cooling to commercial and residential properties in the downtown Honolulu area. On December 19, 2020, Honolulu Seawater Air Conditioning announced it was ending its development and would end operations by the end of January 2021. Honolulu Seawater Air Conditioning is majority owned by
eBay
eBay Inc. ( , often stylized as ebay) is an American multinational e-commerce company based in San Jose, California, that allows users to buy or view items via retail sales through online marketplaces and websites in 190 markets worldwide. ...
founder
Pierre Omidyar
Pierre Morad Omidyar (born Parviz Morad Omidyar, June 21, 1967) is a French-born Iranian-American billionaire and the grandson of General Mahmud Mir-Djalali. A technology entrepreneur, software engineer, and philanthropist, he is the foun ...
's
Ulupono Initiative.
See also
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Sea water air conditioning
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Notes
References
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External links
From Lake Depths, a Blast of Cool for ConsumersCornell University Lake Source Cooling overviewan
details of how it worksGeocean has performed the design and installation of a SWAC system for the Brando Hotel in French Polynesia.
Makai Ocean Engineering has designed SWAC systems in Bora Bora (installed), Kona (installed) and Honolulu, Hawaii, la Reunion, Curaçao, Bahamas, and DWSC systems at Cornell University and Toronto (both installed).
{{DEFAULTSORT:Deep Water Source Cooling
Marine energy
Heating, ventilation, and air conditioning
Renewable energy