District cooling is the cooling equivalent of district heating. Working on broadly similar principles to district heating, district cooling delivers chilled water to buildings like offices and factories needing cooling. In winter, the source for the cooling can often be seawater, so it is a cheaper resource than using electricity to run compressors for cooling. Alternatively, District Cooling can be provided by a Heat Sharing Network which enables each building on the circuit to use a heat pump to reject heat to an ambient ground temperature circuit.
There are also 5th generation district heating and cooling systems (so called cold district heating networks) that are able to provide both heating and cooling simultaneously. In these systems the waste heat from chillers can be recycled and used for space heating or hot water production.
In August 2004, Enwave Energy Corporation, a district energy company based in Toronto, Ontario, Canada, started operating a system that uses water from Lake Ontario to cool downtown buildings, including office towers, the Metro Toronto Convention Centre, a small brewery and a telecommunications centre. The process has become known as Deep Lake Water Cooling (DLWC). It will provide for over 40,000 tons (140 MW) of cooling—a significantly larger system than has been installed elsewhere. Another feature of the Enwave system is that it is integrated with Toronto's drinking water supply. The Toronto drinking water supply required a new intake location that would be further from shore and deeper in the lake. This posed two problems for the utility that managed the city's drinking water supply: 1. the capital cost of moving the water intake location and 2. the new location would supply water that was so cold it would require heating before it could be distributed. The cooperation of the district cooling agency, Enwave, solved both problems: Enwave paid for the cost of moving the water intake and also supplied the heat to warm the drinking water supply to acceptable levels by effectively extracting the heat from the buildings it served. Contact between drinking water and the Enwave cooling system is restricted to thermal contact in a heat exchanger. Drinking water does not circulate through the Enwave cooling systems.
The "Cold Network of Paris" has existed in the city since 1991. The eight production facilities (400 MW) provide cooling to 500 clients for 412 GWh per year. This network is completely managed by Climespace. Since 2002, two other production facilities provide cooling reinforced by ice, in the cooling centers of Opéra/Galfa; they have a total cooling capacity of about 20,000 kWh. Paris also proposes to develop its cold network as part of its climate change plan. As part of the city's climate change plan, two "glaciers" were integrated into the network in 2006 at the Les Halles cooling center, which has a total cooling capacity of about 30,000 kWh: 44 MW come from cooling machines and 13 MW can be added during short periods to the Cold Network of Paris thanks to stocks of ice. Enertherm, located at La Défense, has the largest ice stock in Europe, with a capacity of 240 MWh.
The Helsinki district cooling system uses otherwise wasted heat from summer time CHP power generation units to run absorption refrigerators for cooling during summer time, greatly reducing electricity usage. In winter time, cooling is achieved more directly using sea water. The adoption of district cooling is estimated to reduce the consumption of electricity for cooling purposes by as much as 90 per cent and an exponential growth in usage is forecast. The idea is now being adopted in other Finnish cities.
In Germany, amongst other projects, Munich established a rapidly growing system in 2011 with its core below the Karlsplatz (Stachus), drawing water from the underground Stadtgrabenbach. There's a 24 km network, currently supplying 16 larger organizations. In 2011, the estimated total thermal power output of all district cooling systems in Germany was 160 Megawatt distributed over 90 km.
The Kai Tak Development (KTD) is a huge development project spanning a total area of over 320 hectares covering the ex-airport and nearby areas with large demand for air-conditioning. The HKSAR Government takes the opportunity to implement the District Cooling System (DCS) which is the most energy efficient air-conditioning system in the new development.
The DCS at KTD comprises two central chiller plants, namely the North Plant and the South Plant cum seawater pump house, underground chilled water distribution piping network, seawater supply and discharge pipes and consumer substations located in the buildings to interface with the building’s own chilled water circulation systems.
The cooling capacity of the DCS is about 284 megawatt of refrigeration (MWr) for serving the non-domestic air-conditioned floor area of about 1.73 million m2, equivalent to a cooling supply for 40 nos. of 30-storey high commercial buildings. Upon completion of the project, about 40 kilometres of underground chilled water pipes would have been laid and there would be around 50 buildings in KTD connected to the DCS.
India's first district cooling system is operational in GIFT City ( India's first Operational Smart City). Currently ~10,000 TR capacity is operational which has capacity to upgrade up to 50000 TR.Gujarat International Finance Tec-City in Gujarat.
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A project started in 2012 in Kuwait for the Sabah Al-Salem University City with district cooling. It is capable of cooling a load of 72000 TR and it has two central utility plants with 36 chillers, 36 cooling towers and 2 TES (Thermal Energy Storage) tanks.
On November 9, 2010, the world's largest district cooling plant opened at The Pearl-Qatar. This plant is owned and operated by Qatar District Cooling Company Qatar Cool. It is capable of cooling a load of 130,000 tons (450 MW). The project was built by C.A.T International (part of C.A.T Group).
The Lusail City district cooling system will supply chilled water to end users through an integrated network with a connected cooling of 500,000 Tons of Refrigeration by utilizing multiple chiller plants which are Marina, Wadi, West and North. This will be one of the largest district cooling systems in the world.
Singapore started district cooling with One Raffles Quay, located at Marina Bay in May 2006. The district cooling plant is operated by SP Group's subsidiary, Singapore District Cooling. A second district cooling plant was commissioned in May 2010, which will supply chilled water for the air-conditioning of buildings in the area through pipes housed within the Common Services Tunnel in Marina Bay. The second district cooling plant started operations on 3 March 2016.
Tengah, a planning area and Housing and Development Board (HDB) town, will be the first residential area to have a large-scale centralised cooling system. Centralised chillers installed on the rooftops of some HDB flats pipe chilled water directly to individual units for use in air-conditioners.
The use of district cooling grows rapidly in Sweden as well, in a similar way to Finland.
Working since 1985, the system of the École Polytechnique Fédérale de Lausanne combines, depending on the needs, cooling and heat extraction. This allows for a higher overall energy efficiency of the 19 MW system.
United Arab EmiratesEdit
Emirates District Cooling(Emicool), is a district cooling service provider and a wholly-owned subsidiary of Dubai Investments headquartered in Dubai investments park. It currently has 355,000 tonnes of refrigeration (TR) capacity that connects more than 2,200 buildings in the UAE. It is a member of the Dubai Supreme Council of Energy’s first Association of District Cooling Operators.
Tabreed currently delivers over 1 million refrigeration tons of cooling, across 72 plants located throughout the region, cooling iconic infrastructure projects such as Sheikh Zayed Grand Mosque, Cleveland Clinic, Ferrari World, Yas Mall, Aldar HQ, Etihad Towers, Marina Mall, World Trade Center in Abu Dhabi featuring the Burj Mohammed Bin Rashid, Dubai Metro, Dubai Parks & Resorts, and the Jabal Omar Development in the Holy City of Mecca, alongside several other hotels, hospitals, residential and commercial towers.
In January 2006, PAL technology is one of the emerging project management companies in UAE involved in the diversified business of desalination, sewage treatment and district cooling system. More than 400,000 Tons (1400 MW) of district cooling projects are planned. The Palm Jumeirah utilises district cooling supplied by Palm Utilities LLC to provide air conditioning for buildings on the trunk and crescent of the Palm. The Dubai Metro system, inaugurated in 2009, is the first mass transit network in the world to use district cooling to lower temperatures in stations and trains.
Cornell University'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 tons (50 MW) load.
If the other renewable alternatives are too warm during the summer or too expensive, cold storage can be investigated. In large scale applications underground and snow storage are the most likely alternatives. In an underground storage the winter cold is heat exchanged from the air and loaded into the bedrock or an aquifer by one or more bore holes. In a snow storage frozen water (snow and/or ice) is saved in some kind of storage (pile, pit, cavern etc.). The cold is utilized by pumping melt water to the cooling object, directly in a district cooling system or indirect by a heat exchanger. The lukewarm melt water is then pumped back to the snow where it gets cooled and mixed with new melt water. Snow cooling works as a single cold source but can also be used for peak cooling since there is no relevant cooling limit. In Sweden there is one snow cooling plant in Sundsvall, built and owned by the county. The cooling load in Sundsvall is about 2000 kW (570 tons of refrigeration) and 1500 MWh/year.
Especially in subtropical regions not only cooling, but dehumidifying of the air becomes important. Liquid desiccant cooling allows to generate remotely and efficiently a moisture absorbing liquid. This liquid can be pumped or transported long distances without energy loss. 
DCS consumes 35 percent and 20 percent less electricity as compared to traditional air-cooled air-conditioning systems and individual water-cooled air-conditioning systems using cooling towers respectively. With its high energy efficiency, the implementation of DCS at KTD will achieve estimated annual saving of 85 million kilowatt-hour (kWh) in electricity consumption, with a corresponding reduction of 59,500 tonnes of carbon dioxide emissions per annumal.
Apart from energy saving, DCS would also bring along the following benefits to the consumers:
- Reduction in upfront capital cost for installing chiller plants at their buildings which account for about 5-10% of the total building cost;
- More flexible building designs for consumer buildings as they do not need to install their own chillers and the associated electrical equipment in their buildings;
- Mitigation of heat island effects in KTD and elimination of noise and vibration arising from the operation of heat rejection equipment and chillers of air-conditioning plants in buildings as such equipment will no longer be necessary for buildings subscribing to district cooling services; and
- More adaptable air-conditioning system to the varying demand as compared to individual air-conditioning systems. For each individual building, cooling capacity can be increased by requesting additional cooling capacity from the DCS without carrying out extensive modification works for the building in question.
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