Deep water source cooling
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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. It uses water at 4 to 10 degrees Celsius drawn from deep areas within lakes, oceans, aquifers or rivers, which is pumped through the one side of a heat exchanger. On the other side of the heat exchanger, cooled water is produced.[1]
Basic concept
Water is most dense at 3.98 °C (39.16 °F) at standard atmospheric pressure. 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.
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 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.
Deep lake water cooling allows higher thermodynamic efficiency by using cold deep lake water, which is colder than the ambient
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.[1] 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.
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
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 systsms. In Europe, lake-based heating and cooling could save 0.8 TWh per year, and is most promising in Italy, Germany, Turkey and Switzerland.[2]
Disadvantages
Deep water source cooling requires a large and deep water quantity in the surroundings. To obtain water in the 3 to 6 °C (37 to 43 °F) range, a depth of 50 m (160 ft) to 70 m (230 ft) 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 literatures, 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.[2]
First major system in the United States
First system in Canada
Since August 2004, a deep lake water cooling system has been operated by the
The installed deep lake cooling water intake line was 1,600mm (63") in diameter, 15,000 m (49,213 ft) long and installed at a depth of 85 m (278 ft) 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
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
Salt water air conditioning systems have been used in Sydney's Circular Quay 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. [8][9]
The InterContinental Resort is the largest seawater air conditioning system to date, though there are several other, larger systems being planned.[10] 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.[11] On December 19, 2020, Honolulu Seawater Air Conditioning announced it was ending its development and would end operations by the end of January 2021.[12] Honolulu Seawater Air Conditioning is majority owned by eBay founder Pierre Omidyar's Ulupono Initiative.[13]
See also
- District heating – Centralized heat distribution system
- District cooling – Delivery of chilled water to building needing cooling
- Free cooling – Using low external air temperatures to chill water
- Geothermal heat pump – System to transfer heat to/from the ground
- Sea water air conditioning
- Seasonal thermal energy storage – Storage of heat or cold for periods of up to several months
- Solar pond – Solar thermal energy
- Ocean energy – Energy stored in the waters of oceans
- Ocean thermal energy conversion – Extracting energy from the ocean
Notes
- ^ OSTI 272719. Archived from the original on 2012-02-16.)
{{cite conference}}
: CS1 maint: unfit URL (link - ^ S2CID 257618187.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ^ "Lake Source Cooling". Facilities and Campus Services. Cornell University. Archived from the original on 2020-07-02. Retrieved 2020-07-18.
- ^ "A Brief History of Enwave". Enwave. Archived from the original on 2007-12-30.
{{cite web}}
: CS1 maint: unfit URL (link) - ^ "Toronto". Enwave. Archived from the original on 2020-04-06. Retrieved 2020-07-21.
- .
- ^ "Seawater/Lake Water Air Conditioning (SWAC/LWAC)". Ocean Thermal Energy Corporation. Archived from the original on 2020-06-07. Retrieved 2020-07-21.
- ^ "AMP Building". Sydney Living Museums. Archived from the original on 2020-06-06. Retrieved 2020-07-21.
- ^ "Lend Lease looks to Sydney Harbour for water cooling at Barangaroo". The Fifth Estate. November 20, 2012. Archived from the original on 2020-06-06. Retrieved 2020-07-21.
- ^ "The Basics of Seawater Air Conditioning Explained". YouTube. Retrieved 2020-07-21.
- ^ Lincoln, Mileka (6 August 2013). "$1M local investment in Honolulu Seawater Air Conditioning". Hawaii News Now. Archived from the original on 2020-07-21. Retrieved 2020-07-21.
- ^ "Honolulu Seawater Air Conditioning to end development after 15 years". www.bizjournals.com. Retrieved 2020-12-21.
- Pacific Business News. Archivedfrom the original on 2015-03-28. Retrieved 2020-07-21.
References
- Sudick, Jennifer (January 15, 2008). "New seawater cooling plant in the works". Honolulu Star-Bulletin. Vol. 13, no. 15. Archived from the original on 2008-11-20. Retrieved 2008-04-26.
- Godvin, Tara (April 7, 2005). "Using Cold Seawater for Air-Conditioning". Long Beach Press-Telegram. Associated Press – via NewsBank.
External links
- From Lake Depths, a Blast of Cool for Consumers
- Cornell University Lake Source Cooling overview and details of how it works
- Geocean Archived 2020-07-21 at the Wayback Machine has performed the design and installation of a SWAC system for the Brando Hotel in French Polynesia.
- Makai Ocean Engineering Archived 2014-02-01 at the Wayback Machine 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).