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District Cooling:

District cooling means the centralized production and distribution of cooling energy. Chilledwater is delivered via an underground insulated pipeline to office, industrial and residential

 buildings to cool the indoor air of the buildings within a district. Specially designed units in each

 building then use this water to lower the temperature of air passing through the building's air conditioning system.

The output of one cooling plant is enough to meet the cooling-energy demand of dozens of  buildings. District cooling can be run on electricity or natural gas, and can use either regular 

water or seawater. Along with electricity and water, district cooling constitute a new form of 

energy service.

District cooling is measured in refrigeration ton which is equivalent to 12000 BTU's per hour.

Refrigeration Ton is the unit measure for the amount of heat removed. Refrigeration Ton isdefined as the heat absorbed by one ton of ice (2000 pounds) causing it to melt completely by the

end of one day (24 hours).

District cooling systems can replace any type of air conditioning system, but primarily compete

with air-cooled reciprocating chiller systems serving large buildings which consume large

amounts of electricity. This air-conditioning system is subject to a difficult operatingenvironment, including extreme heat, saline humidity and windborne sand. Over time, performance, efficiency and reliability suffer, leading to significant maintenance costs and

ultimately to equipment replacement.

Empowers District Cooling system is underpinned by a skilled around-the-clock service team

and a comprehensive set of emergency back-up systems that ensure complete reliability and ease

of use.

Due to its huge size and mega load requirements District cooling can be performed by two methods

1.  Using a Vapor Absorption Chiller 

2.  Using sea water below 5 degree Celsius for direct cooling

  If the water is below 5 degree Celsius it can be used directly and no further cooling of it

is required

  If the water achieved from sea is above 5 degree Celsius it is needed to be chilled in a

chiller preferably a vapor absorption chiller 

Vapor Absorption Chiller:

A vapor absorption chiller or a vapor absorption cycle uses absorption process rather than compression to

run the process i.e. it needs heat rather than electricity to maintain an air-conditioned space. It may use

Lithium Bromide and water solution or Ammonia and water solution in the cycle. The heat required for 

the process can be received from solar, thermal, fuel powered or waste heat resources.

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Using sea water is explained very briefly with animation in this article:

http://www.makai.com/pipelines/ac-pipelines/  

Cogeneration System:

A co-generation system is a system where two systems co-exist with each other and the cycles work together in harmony with each other. A generator producing electricity throws out sufficient heat through

exhaust gases these gases can be used to drive a Vapor absorption chiller. If a chiller is installed at the

exhaust of the generator the resulting system would be called a Cogeneration system. Another example of 

a cogeneration system would be a gas turbine exhaust running a steam turbines boiler. Both are also

examples of waste heat recovery.