Deep lake water cooling
Encyclopedia
Deep lake water cooling uses cold water pumped from the bottom of a lake as a heat sink
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.
Air conditioners are heat pump
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 systems do not transfer heat directly into the exterior air. The thermodynamic efficiency of the overall system can be improved by utilizing evaporative cooling, where the temperature of the cooling water is lowered close to the wet-bulb temperature
by evaporation in a cooling tower
. This cooled water then acts as the heat sink for the heat pump.
Deep lake water cooling allows an even higher thermodynamic efficiency by utilizing the deep lake water, which is at a lower heat rejection temperature 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.
'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) load.
Lake water enters the system via a screened intake structure 10400 feet (3,169.9 m) away in 250 feet (76.2 m) of water. The intake pipeline is 63 inches (1.6 m) High Density Polyethylene (HDPE) that was deployed from the surface using a "controlled" sink process where water was pumped in at the shallow end and air was released at the other end. A series of stiffener rings and concrete collars keep the pipeline on the lake floor and protect it from mechanical forces. The outfall is 48 inches (1,219.2 mm) HDPE and is approximately 750 feet (228.6 m) long. The last 100 feet (30.5 m) of the outfall has 38 six-inch (152 mm) nozzles, about 1 foot (0.3048 m) above the bottom of the lake floor in 14 feet (4.3 m) of water, pointed up at a 20 degree angle and pointed north only. This helps promote mixing of the return water into the receiving water. The water cools a heat-exchanger which is connected to a closed-loop campus chilled water distribution system linked to many buildings on the main campus.
, Ontario
. It draws water from Lake Ontario
through tubes extending 5 kilometres (3.1 mi) into the lake, reaching to a depth of 83 metres (272.3 ft). 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 3200000 square metre of office space.
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. The Enwave system only uses water that is destined to meet the city's domestic water needs. Therefore, the Enwave system does not pollute the lake with a plume of waste heat.
Resort and Thalasso-Spa on the island of Bora Bora
uses an OTEC 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 directly (no conversion to electricity takes place). Similar systems are also in place in The Excelsior hotel and The Hongkong and Shanghai Banking Corporation main building in Victoria City
, Hong Kong
.
s which were used to store ice throughout the year prior to the invention of refrigeration
. Icehouses were filled with fresh ice collected from lake surfaces during the winter whereas deep lake water cooling taps a permanent store of cold water.
(OTEC) does. However, OTEC is intended to be used for generating energy by operating a heat engine
on the temperature difference between the ocean bottom and the ocean surface. Deep lake water cooling bypasses the need for electricity generation altogether and, so, is a simpler and more immediately practical technology than OTEC. Ambitious OTEC projects have yet to realize their full potential because they present far more demanding engineering challenges.
Heat sink
A heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...
for climate control systems
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
. Because heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
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
Geothermal
Geothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
sinks, but generally simpler to construct given a suitable water source.
Basic concept
Water is most dense at 3.98 °C (39.2 °F) at standard atmospheric pressure. Thus as water cools below 3.98 °C it decreases in density and will rise. 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
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
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 systems do not transfer heat directly into the exterior air. The thermodynamic efficiency of the overall system can be improved by utilizing evaporative cooling, where the temperature of the cooling water is lowered close to the wet-bulb temperature
Wet-bulb temperature
The wet-bulb temperature is a type of temperature measurement that reflects the physical properties of a system with a mixture of a gas and a vapor, usually air and water vapor. Wet bulb temperature is the lowest temperature that can be reached by the evaporation of water only. It is the...
by evaporation in a cooling tower
Cooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
. This cooled water then acts as the heat sink for the heat pump.
Deep lake water cooling allows an even higher thermodynamic efficiency by utilizing the deep lake water, which is at a lower heat rejection temperature 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.
First major system in the United States
Cornell UniversityCornell University
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
's Lake Source Cooling System uses Cayuga Lake
Cayuga Lake
Cayuga Lake is the longest of central New York's glacial Finger Lakes, and is the second largest in surface area and second largest in volume. It is just under 40 miles long. Its average width is 1.7 miles , and it is at its widest point near Aurora...
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
Ithaca City School District
The Ithaca City School District is a public school district centered in Ithaca, Caroline, Danby, Dryden and Enfield. Approximately 500 teachers work in the district, along with 100 other professional staff members and 200 paraprofessionals....
. 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) load.
Lake water enters the system via a screened intake structure 10400 feet (3,169.9 m) away in 250 feet (76.2 m) of water. The intake pipeline is 63 inches (1.6 m) High Density Polyethylene (HDPE) that was deployed from the surface using a "controlled" sink process where water was pumped in at the shallow end and air was released at the other end. A series of stiffener rings and concrete collars keep the pipeline on the lake floor and protect it from mechanical forces. The outfall is 48 inches (1,219.2 mm) HDPE and is approximately 750 feet (228.6 m) long. The last 100 feet (30.5 m) of the outfall has 38 six-inch (152 mm) nozzles, about 1 foot (0.3048 m) above the bottom of the lake floor in 14 feet (4.3 m) of water, pointed up at a 20 degree angle and pointed north only. This helps promote mixing of the return water into the receiving water. The water cools a heat-exchanger which is connected to a closed-loop campus chilled water distribution system linked to many buildings on the main campus.
First system in Canada
Since August 2004, a deep lake water cooling system has been operated by the Enwave Energy Corporation in TorontoToronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. It draws water from Lake Ontario
Lake Ontario
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south by the American state of New York. Ontario, Canada's most populous province, was named for the lake. In the Wyandot language, ontarío means...
through tubes extending 5 kilometres (3.1 mi) into the lake, reaching to a depth of 83 metres (272.3 ft). 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
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
of 59,000 tons (207 MW). The system currently has enough capacity to cool 3200000 square metre of office space.
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. The Enwave system only uses water that is destined to meet the city's domestic water needs. Therefore, the Enwave system does not pollute the lake with a plume of waste heat.
Ocean water cooling
The InterContinentalInterContinental
InterContinental is a brand of upscale luxury hotels, founded by Pan American World Airways, under Juan Trippe, and now owned by InterContinental Hotels Group. The chain operates over 200 hotels and resorts in approximately 75 nations.-History:...
Resort and Thalasso-Spa on the island of Bora Bora
Bora Bora
The commune of Bora-Bora is made up of the island of Bora Bora proper with its surrounding islets emerging from the coral reef, 29.3 km² in total, and of the atoll of Tupai , located north of Bora Bora...
uses an OTEC 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 directly (no conversion to electricity takes place). Similar systems are also in place in The Excelsior hotel and The Hongkong and Shanghai Banking Corporation main building in Victoria City
Victoria City
Victoria, Victoria City, or statutorily, the City of Victoria, was one of the first urban settlements in Hong Kong after it became a British colony in 1842. It was initially named Queenstown but was soon known as Victoria...
, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
.
Comparison to related technologies
This water-cooling technology has some relationship to an older technology and a possible future technology.Icehouse cooling
Looking back to the past, water-cooling recalls well insulated icehouseIcehouse (building)
Ice houses were buildings used to store ice throughout the year, prior to the invention of the refrigerator. Some were underground chambers, usually man-made, close to natural sources of winter ice such as freshwater lakes, but many were buildings with various types of insulation.During the...
s which were used to store ice throughout the year prior to the invention of refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
. Icehouses were filled with fresh ice collected from lake surfaces during the winter whereas deep lake water cooling taps a permanent store of cold water.
OTEC power generation
Looking towards the future, water-cooling uses cold deep water just as ocean thermal energy conversionOcean thermal energy conversion
Ocean Thermal Energy Conversion uses the difference between cooler deep and warmer shallow or surface ocean waters to run a heat engine and produce useful work, usually in the form of electricity....
(OTEC) does. However, OTEC is intended to be used for generating energy by operating a heat engine
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...
on the temperature difference between the ocean bottom and the ocean surface. Deep lake water cooling bypasses the need for electricity generation altogether and, so, is a simpler and more immediately practical technology than OTEC. Ambitious OTEC projects have yet to realize their full potential because they present far more demanding engineering challenges.
See also
- Solar pondSolar pondA solar pond is a pool of saltwater which acts as a large-scale solar thermal energy collector with integral heat storage for supplying thermal energy...
- District heatingDistrict heatingDistrict heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...
- Ocean energy
- TrigenerationTrigenerationTrigeneration, also called CCHP , refers to the simultaneous generation of electricity, useful heating and useful cooling from the same original heat source such as fuel or solar energy...
External sources
- Enwave -- Corporate page on Enwave and Toronto's deep lake water cooling system.
- From Lake Depths, a Blast of Cool for Consumers
- Cornell University Lake Source Cooling Website
- Makai Ocean Engineering