District cooling
District cooling is the opposite 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 sea water, so it is a cheaper resource than using electricity to run compressors for cooling.
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.[1] The idea is now being adopted in other Finnish cities. The use of district cooling grow also rapidly in Sweden in a similar way.[2]
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.
In August 2004, Enwave Energy Corporation, a district energy company based in Toronto, 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 additionally, 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. [citation needed]
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 to provide air conditioning.
In 2006, a district cooling system came online in Amsterdam's Zuidas, drawing water from the Nieuwe Meer[3][4]
On the 9th of November 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). [5]
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.[6] 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.[7]
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. [8]
References
- ^ [1][dead link]
- ^ "Energiläget 2007" (PDF). Swedishenergyagency.se. Retrieved 2011-09-25.
- ^ Lake water air conditioning cuts CO2 emissions by 70% compared to conventional cooling
- ^ "District cooling in Amsterdam's Zuidas" (PDF). Retrieved 2011-09-25.
- ^ "World's largest district cooling plant opens at The Pearl Qatar". Gulf-times.com. Retrieved 2011-09-25.
- ^ http://epubl.ltu.se/1402-1544/2005/30/LTU-DT-0530-SE.pdf
- ^ "The Sundsvall snowcooling plant - large scale snowcooling | Snowpower". Snowpower.se. Retrieved 2011-09-25.
- ^ "L-DCS in District Cooling Systems".