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Deep lake water cooling uses cold water pumped from the bottom of a lake as a heat sink
Heat sink

A heat sink is an environment or object that absorbs and dissipates heat from another object using thermal contact . Heat sinks are used in a wide range of applications wherever efficient heat dissipation is required; major examples include refrigeration, heat engines, Thermal management of electronic devices and systems and lasers....
 for climate control systems
Air conditioning

An air conditioner is an appliance, system, or Mechanism designed to extract heat from an area via a refrigeration cycle. In construction, a complete system of heating, Ventilation , and air conditioning is referred to as "HVAC." Its purpose, in a building or an automobile, is to provide comfort during either hot or cold...
. Because heat pump
Heat pump

A heat pump is a machine or device that moves heat from one location to another location using mechanical work. Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink....
 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:* Geothermal , heat that comes from within the Earth...
 sinks, but generally simpler to construct given a suitable water source.

Basic concept
Water is most dense at at standard atmospheric pressure.






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Deep lake water cooling uses cold water pumped from the bottom of a lake as a heat sink
Heat sink

A heat sink is an environment or object that absorbs and dissipates heat from another object using thermal contact . Heat sinks are used in a wide range of applications wherever efficient heat dissipation is required; major examples include refrigeration, heat engines, Thermal management of electronic devices and systems and lasers....
 for climate control systems
Air conditioning

An air conditioner is an appliance, system, or Mechanism designed to extract heat from an area via a refrigeration cycle. In construction, a complete system of heating, Ventilation , and air conditioning is referred to as "HVAC." Its purpose, in a building or an automobile, is to provide comfort during either hot or cold...
. Because heat pump
Heat pump

A heat pump is a machine or device that moves heat from one location to another location using mechanical work. Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink....
 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:* Geothermal , heat that comes from within the Earth...
 sinks, but generally simpler to construct given a suitable water source.

Basic concept


Water is most dense at at standard atmospheric pressure. Thus as water cools below 3.98 °C it decreases in density and will rise, the most obvious example being that ice floats. 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 moves heat from one location to another location using mechanical work. Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink....
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 physics properties of a physical system with a mixture of a gas and a vapor, usually air and water vapor....
 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 temperature or rely solely on air to cool the working fluid to near the Dry-bulb temperature....
. 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 University
Cornell University

Cornell University located in Ithaca, New York, USA, is a private university with four Statutory college. Its two medical campuses are in New York City and Education City, Qatar....
's Lake Source Cooling System uses Cayuga Lake
Cayuga Lake

Cayuga Lake is the longest of western New York's glacial Finger Lakes, and is the largest in surface area and second largest in volume. It is just under 40 miles long....
 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, New York, New York, consisting of 12 schools and with a total enrollment of approximately 5,500 students....
. 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
Ton

Units of massThere are several similar units of mass or volume called the ton:Others*The long ton is used for petroleum products such as aviation fuel....
 (51 megawatt) load.

Lake water enters the system via a screened intake structure away in of water. The intake pipeline is 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 HDPE and is approximately long. The last of the outfall has 38 six-inch (152 mm) nozzles, about above the bottom of the lake floor in 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 Toronto
Toronto

Toronto is the List of the 100 largest municipalities in Canada by population in Canada and the Provinces and territories of Canada Provincial and territorial capitals of Canada of Ontario....
, Ontario
Ontario

Ontario is a Provinces and territories of Canada located in the Central Canada part of Canada, the largest by population and second largest, after Quebec, in total area....
. It draws water from Lake Ontario
Lake Ontario

Lake Ontario is one of the five Great Lakes of North America. The lake is bounded on the north by the Canadian province of Ontario and on the south by Ontario's Niagara Peninsula and by the U.S....
 through tubes extending into the lake, reaching to a depth of . 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 an appliance, system, or Mechanism designed to extract heat from an area via a refrigeration cycle. In construction, a complete system of heating, Ventilation , and air conditioning is referred to as "HVAC." Its purpose, in a building or an automobile, is to provide comfort during either hot or cold...
 of 59,000 tons (207 MW). The system currently has enough capacity to cool 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 InterContinental Resort and Thalasso-Spa on the island of Bora Bora uses a cold seawater system to air-condition its buildings.[11] 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).

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 icehouse
Icehouse (building)

Ice houses were buildings used to store ice throughout the year, prior to the invention of the refrigerator. The most common designs involved underground chambers, usually man-made, which were built close to natural sources of winter ice such as freshwater lakes....
s which were used to store ice throughout the year prior to the invention of refrigeration
Refrigeration

Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable....
. 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 conversion
Ocean thermal energy conversion

Ocean thermal energy conversion is a method for generating electricity which uses the temperature difference that exists between deep and shallow waters to run a heat engine....
 (OTEC) does. However, OTEC is intended to be used for generating energy by operating a heat engine
Heat engine

A heat engine is a physical or theoretical device that converts thermal energy to mechanical output. The mechanical output is called Mechanical work, and the thermal energy input is called heat....
 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 pond
    Solar pond

    A solar pond is large-scale solar thermal energy collector with integral heat storage for supplying thermal energy. A solar pond can be used for various applications, such as process heating, water desalination, solar refrigeration, drying and solar power generation....
  • District heating
    District heating

    District 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
    Ocean energy

    The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Many researches show that ocean energy has the potentiality of providing for a substantial amount of new renewable energy around the world....
  • Trigeneration
    Trigeneration

    Trigeneration or trigen is the simultaneous production of mechanical power , heat and cooling from a single heat source such as fuel or solar energy....


External sources

  • -- Corporate page on Enwave and Toronto's deep lake water cooling system.