Working on a computer in a block with large glass windows, storing perishable food or maintaining hi-tech equipment - lifestyles in the 21st century increase the demand for cooled environments. The refrigeration and cooling market is fast growing, with different solutions being offered, from individual to centralized air-conditioning. And of course, what is often the most appropriate solution - cooling networks.
Cooling networks
Lowering the temperature with heat exchangers
A strategic choice for new developments
Construction of a cooling network is a significant investment, especially since the pipes that supply refrigeration and carry the heat back are very large, and the water supplied must be very cold. Networks are an ideal solution when three conditions are met:sufficiently high year-round demand, a high concentration of industrial and/or commercial activity, and a real estate contractor or developer that supports this solution from the project outset. Furthermore, two district development partners are essential:the local authorities or contractors, who draw up the general specifications, and the real estate developers who decide on the hook-ups for new buildings.
More and more satisfied customers worldwide
Although cooling networks represent a modest share of Dalkia's business, they are not a new activity.The SUC network in La Défense (see inset) has been operating since the 1970s, for example. However, the number of satisfied customers has increased in recent years.
> 2006: Singapore Marina South; the Guangzhou University campus and stores and offices in Chongqing, China; city of Montreal.
> 2007: Bahrain Bay and Al Aren in Bahrain; the largest portfolio of cooling networks in the United States (Las Vegas, Atlanta, Los Angeles, etc), following the acquisition of Thermal North America; Paik university hospital in Seoul, South Korea.
Many new projects are on the cards for the future, particularly in emerging economies, where Dalkia is building on its expertise.
Dalkia and cooling - comprehensive proficiency in a complex field
Customers of cooling networks and heating networks expect the same things from us - service quality,energy efficiency and environmental protection. A cooling network will therefore need to be very efficient at optimizing production, especially since a wider range of challenges will need to be incorporated:water scarcity as in Bahrain (see inset) and a desire to reconcile comfort with energy conservation.
•Energy efficiency + 40% compared with independent air-conditioning for a building •18 cooling networks in 2007 •564 MW installed |
Concentration means better cooling
Like heating networks, cooling networks centralize production, thereby lowering the cost for the end customer. In each block or warehouse, the absence or removal of individual equipment frees up useful space. Neither do connected buildings need powerful, complicated electrical installations. Future occupants are not only guaranteed the comfort of air-conditioning, but also the assurance of enhanced safety.
35 years of experience in the La Défense business district in Paris
SUC (Société Urbaine de Climatisation) manages a 73.5 MW chilled water production and distribution network on the banks of the Seine. The network, which cools 50% of the buildings in La Défense, has changed radically since it was commissioned in 1972. The plant, which once produced a huge cloud of steam, is now an invisible part of the business district, hidden beneath a large office block. The cooling towers were replaced in 1992 by a station pumping water from the Seine. Awareness of environmental issues has prompted profound changes. In line with new regulations, the CFC-type refrigerant fluids (R500) were replaced by HFCs (R134A), after complete refurbishing of the unit and its surroundings. As a result of these innovations, in 1999 the company was one of the first in France to obtain ISO 14001 environmental certification.
The 17-strong team responds to the needs of increasingly demanding customers on a daily basis. "Only the tiniest variation in water delivery temperature, contractually set at 4.5°C, is now tolerated," explains Roger Aguilera, SUC's head of operations. "We must supply cooling to customers whose facilities are their nerve centers. Many banks and insurance companies, for example, have set up their trading rooms in La Défense - and the computers do not tolerate any overheating!" Roger Aguilera and his team must supply the right power at the right time, a skill which comes from many years of experience. "There is consumption peak at 11:30 a.m., when the kitchens begin cooking, and at 4:30 p.m.,when the early leavers let heat in through the swing doors. In winter, too, airconditioning is vital, because when a low sun hits the glass walls horizontally, the temperature inside rises very quickly." The future promises yet more challenges. In theory, very severe flooding could inundate the pumping station. SUC has anticipated this risk by building a second station, capable of operating underwater. And the renovation plan for La Défense will force the company to double its production capacity by 2015.The "old lady" still has many happy days ahead.
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Bahrain Bay - cooling an island
In the Kingdom of Bahrain, a new island is emerging from the blue waters of the Persian Gulf - Bahrain Bay. It is a mixed-use project of housing, hotels and offices totaling 1.5 million square meters. Signed in 2007, the contract, worth €110 million, includes utilities management (chilled water, watering systems, wastewater collection and treatment and drinking water distribution). This has been supplemented by a comprehensive building management contract for all infrastructure, including public parks, roads, bridges and public lighting.
> The utilities management contract covers a large cooling network:4.2 kilometers of pipes, 160 MW of cooling capacity with 20 chilled water units, and a wastewater treatment center with a capacity of 7,000 cubic meters per day. In order to get around the lack of water in Bahrain, Dalkia will reuse wastewater from 20,000 people, and will pump water directly from the sea to top up the cooling towers with untreated brine. "The contractwas won thanks to a holistic approach,not simply focused on production of chilled water," says Arnaud Martinez, Project Manager for Bahrain Bay. "As well as frugal management of water resources, we have used a series of very innovative technical solutions." For instance,the installation of refrigeration units in parallel rather than in series to optimize temperature variations between the units and the use of a variable primary flow rate to reduce the number of pumps increases the plant's efficiency and performance, while reducing its footprint.
> Arnaud Martinez sees a very promising future for Dalkia's cooling networks in the Middle East. "The Bahrain Bay contract and the presence of a team on the ground have already led to signing of the 90 MW Al Aren contract in May 2007.These utilities distribution contracts should lead to many maintenance and comprehensive building management contracts." New projects are currently being negotiated in the Middle East, in particular in Bahrain and Saudi Arabia.
Cooling systems discharge excess heat from premises to the outside, as Bertrand Guillemot, Head of the Expertise and Technical Support Department in the Technical Division, explains. "Like a heating network, a cooling network is made up of three parts:the production plant, the network of pipes and the delivery points. Chilled water travels from the plant to the customer, absorbing heat, and returns to its departure point warmer. The plant releases this heat outside, into the air using cooling towers or into a river or the sea through a water outlet.The network is a closed system, cooled to a temperature between 2°C (or even 0.5°C in some networks we recently acquired in the United States) and 12°C. Water returns at a temperature between 10 and 20°C. The energy performance, the coefficient of performance (COP), is the ratio of the amount of energy leaving to the amount of energy entering. The COP is generally between three and four." |
Two types of cold-production units > Compression chillers. The compressor draws in low-pressure refrigerant gas and compresses it. It is then cooled to a liquid. The heat is released outside, to the air, river or sea. The fluid enters a system that expands the compressed liquid. It then cools the water in the system and evaporates into a gas that returns to the compressor. This common technology is a mechanical process that is flexible to use. |
Free cooling and cold storage > Free cooling makes it possible to turn off the units and use low outside temperatures directly(sea, river or air). COPs can increase to as much as 30. |