By Norman Quesnel, Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc.
(This article will be featured in an upcoming issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine. To read other stories from Norman Quesnel, visit https://www.qats.com/cms/?s=norman+quesnel.)
District cooling is the centralized production and delivery of cooling energy to collective regions of office, public or domestic structures. In a typical district cooling scheme, a central plant chills water from a contained reservoir or taken from an ocean or lake. The chilled water is delivered via underground, insulated pipelines to select buildings in a district. The buildings contain pumps and tubing systems that circulate the cold water within the living areas.
Air is forced past the circulating cold water to produce an air conditioned environment. The resulting warmed water in the tubes is returned to the central plant for re-chilling and recirculating.
District cooling can use either regular water or seawater and can be powered by electricity or natural gas. The output of one district cooling plant is enough to meet the cooling-energy demands of dozens of buildings. [1]
Nowhere is advanced district cooling being developed more than in the Middle East, particularly in its wealthier – and hotter – countries like those in the Gulf Cooperation Council (GCC): Saudi Arabia, Kuwait, United Arab Emirates (UAE), Qatar, Bahrain and Oman. Air conditioning is responsible for about 70 percent of the GCC’s electricity demand during peak summer months.
Figure 1. CAD Image of District Cooling in a High-Rise Building in Lusail City, an Urban Development Planned for Qatar. [2]
One district cooling example is Qatar’s very smart Lusail City. Still largely in planning, Lusail will use a state-of-the-art system to provide cool environments in its modern business and residential buildings. In typical fashion, the Lusail system will use chilled water in pipes feeding to different localities via an extensive system of underground tunnels and local substations. [2]
High Cooling Performance
In many ways, district cooling is a superior alternative to conventional, localized air conditioning. It helps reduce costs and energy consumption for both customers and governments alike, while also protecting the environment by cutting carbon dioxide emissions.
Figure 2. District Cooling Systems can Store 30% of Potential Cooling Output by Holding Water in Reserve for Seasonal Requirements. [3]
Some of the advantages district cooling has over traditional air conditioning includes 50 percent less energy consumption with better accommodation of peak cooling power demands. There are substantially lower maintenance costs than for individual, localized units. District cooling’s equipment has, on average, a 30-year working life, just about as long as conventional urban air conditioning systems.
District cooling systems reduce CO2 emissions because of their lower energy consumption. The centralized systems also free up useable space in individual buildings, including rooftops and basements where local cooling systems were formerly installed. [3]
Figure 3. District Cooling Layout for King Abdullah Financial District (KAFD) Under Construction Near Riyadh, Saudi Arabia. Total Capacity is 100,000 Tons of Refrigeration. [4]
District cooling is measured in tons of refrigeration, TRs, equivalent to 12,000 BTUs per hour. A refrigeration ton is the unit of measure for the amount of heat removed. It is defined as the heat absorbed by one ton (2,000 pounds) of ice causing it to melt completely by the end of one day (24 hours). In Qatar and Saudi Arabia, the district cooling systems being developed will contribute a combined 4.5 million tons of refrigeration.
Figure 4. District Cooling at the Nation Towers Area of Abu Dhabi is Managed by Tabreed, Which has 71 District Cooling Plants Throughout the Gulf Cooperation Council, GCC. [5]
Nation Towers is the site of two skyscrapers near the southern end of the ocean-bordering Corniche in Abu Dhabi, the capital of the UAE. The towers, 65 and 52 floors tall respectively, are joined by a sky bridge and together offer nearly 300,000 m2 of usable space.
The towers and the surrounding structures are air conditioned by a district cooling plant managed by Tabreed, the largest name in district cooling in the GCC. In 2015, per Tabreed, the company’s UAE-based district cooling systems reduced the amount of energy used in air conditioning by 1.3 billion kilowatt hours – the equivalent use of 44,000 UAE homes. [6]
Northeast from Abu Dhabi, the UAE city of Dubai is home to the sprawling WAFI Mall. The site uses Siemens Demand Flow technology to optimize the chilled water system that keeps its stores and restaurants at comfortable temperatures. Siemens Demand Flow technology uses specialized algorithms to optimize the entire chilled water system of a cooling plant, delivering energy savings of between 15 and 30 percent.
By simplifying operations, increasing the cooling capacity and improving efficiency, the system is able to reduce flow in periods of lesser demand, lowering operation and maintenance costs and significantly lowering energy use. [7]
But the Middle East is not the only part of the world employing district cooling. In another warm country, India, a new business district is being constructed on nearly 900 acres in the state of Gujarat. This is the Gujarat International Finance Tec-City, whose district cooling will provide a total cooling capacity of 1,800,000 TR. [8]
In Europe, Copenhagen is home to a successful district cooling operation. The city may not be thought of as in much need of air conditioning; summer high temperatures rarely exceed the mid-70s Fahrenheit. But even in Denmark, there is a need for indoor cooling inside buildings with large server rooms or where many people work or shop. The northern city already had a district heating system and harnessed much of that infrastructure to add cooling.
Figure 5. Copenhagen’s District Cooling System Reduces Carbon Emissions by Nearly 70% and Electricity Consumption by 80% Compared to Conventional Cooling. [5] (Pictured: Heat pipes running under Copenhagen/Wikimedia Commons)
At times Copenhagen’s ocean water is so cold it doesn’t need to be chilled, which saves energy. The district cooling is targeted for co-located buildings (department stores, commercial buildings, hotels, and facilities with data centers) with cooling demands of 150 kilowatts (kW) or more. [9]
And in the U.S., Thermal Chicago provides the country’s biggest district cooling system. It includes five interconnected plants providing cooling to more than 100 buildings in the Windy City. During peak time of air conditioner use, the Thermal Chicago cooling system has reduced energy demand by more than 30 megawatts.
The facility’s also uses a different water-chilling technology that includes an ice-based thermal storage tank for faster cooling and return of chilled water to the infrastructure needing cooling. A YouTube video explains how Thermal Chicago water cooling is set up. [10]
Figure 6. Ice-based Cooling Section Within the Thermal Chicago District Cooling System, from YouTube Video. [10]
Recapping the basic steps of district cooling:
• A central plant chills water.
• A primary water circuit then distributes the chilled water to buildings through an underground insulated pipes network.
• A secondary water circuit in the customers’ building circulates the cold water.
• Air is then forced past the cold water tubing to produce an A/C environment.
• The warmer water of the primary circuit is returned to the central plant to be re-chilled and recycled.
District cooling is not a new technology, or even a new concept. Centralized production and distribution of temperature control has been in commercial use since the 19th century, mainly for heating purposes.
Today, for efficiency and environmental reasons – including rising global temperatures – district cooling is seeing a renaissance by being designed into many of the smarter cities being built around the world.
References
1. Tabreed, https://www.tabreed.ae/en/district-cooling/district-cooling-overview.aspx
2. Lusail City, http://www.lusail.com
3. CELCIUS Smart Cities, http://celsiuscity.eu/
4. Saudi Tabreed, http://www.fleminggulf.com/files/doc/DBUT09/Abdul_Jalil_Bakhruji.pdf
5. Tabreed, https://www.tabreed.ae/en/district-cooling/our-district-cooling-plants.aspx
6. The National UAE, http://www.thenational.ae/uae/environment/tabreed-reduces-carbon-emissions
7. Siemens, http://www.middleeast.siemens.com/me/en/news_events/news/news-2016/siemens-smart-building-tech-can-cut-gccs-cooling-bill-by-40.htm
8. Gujarat International Finance Tec-City, http://giftgujarat.in/district-cooling-system
9. Forbes, https://www.forbes.com/sites/justingerdes/2012/10/24/copenhagens-seawater-cooling-delivers-energy-and-carbon-savings/#1f8d40d74245
10. Thermal Chicago video, https://www.youtube.com/watch?v=ziEbY0oLf-o
For more information about Advanced Thermal Solutions, Inc. thermal management consulting and design services, visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.