While energy-intensive air conditioners are increasingly being installed to combat global warming, urban cooling networks offer an alternative. But what are the advantages and disadvantages?
Although designed to cool our homes and workplaces, air conditioners run on coal, oil or gas and increase planet-warming greenhouse gas emissions. Often installed on the facades of buildings, air conditioning units also contribute to warming cities by releasing waste heat.
They also use a lot of electricity on hot days, which can overload the grid and contribute to blackouts. To solve these problems, many large cities such as Paris, Munich, Hong Kong, Singapore, Dubai and Toronto are building large, efficient central cooling systems that use less electricity.
There they are used by hospitals, hotels, data centers and large buildings and work by pumping cold water through a network of pipes.
In modern cooling technology used in refrigerators, air conditioners, and heat pumps, gas is compressed in a closed system where it becomes vapor. Heat release process. The pressure then drops, causing the steam to heat up again and become a gas. During this process, thermal energy is extracted, creating a cooling effect.
Thanks to various measures, large refrigeration plants can produce refrigeration in a more environmentally friendly way than small plants.
For example, many city utilities use natural cooling sources from rivers, groundwater, lakes or the sea. This also means that these installations require less energy.
“We try to use groundwater or municipal waterways as sources,” says Stefan Dworschak of Stadtwerke München, a city-owned utility that supplies electricity to more than 95% of Munich households. provide as much primary cooling as possible.” Like other district cooling networks, the one in Munich in southern Germany has ice storage facilities. Ice is produced there using large refrigeration units, especially at night, "when the city's electricity consumption is low, which puts less strain on the city," Dworschak told DW. grid".
Cold air generated at night is then released during the day to meet the cooling needs of buildings.
Thermal cooling: absorption cooling
However, cooling can also be produced by heat. For example, in the Austrian capital Vienna, waste heat from a waste incineration plant is used to power absorption chillers.
By intelligently combining different technologies, natural cooling sources and existing waste heat, central cooling systems typically require less electricity. In Munich, according to Dworschak, savings from centralized cooling compared to decentralized cooling are “50 to 70 percent.”
Combining cooling and heating technology saves energy
Just like district heating networks, district cooling networks also have disadvantages. Investment costs are high and pipes must be laid underground in the city and connected to buildings. Cooling and heating energy is lost as it passes through long underground pipes.
These losses are especially high if the water gets too hot or too cold during transport. Experts highlight the potential for savings thanks to the installation of combined heating and cooling networks, which are increasingly common in Europe.
One such example can be found in the Moosach district of Munich. There, the city's data center is connected to the district's cooling network that uses cold air to cool the servers and pumps hot water into the cooling network's return line.
A few hundred meters away, this hot water source is used for a building's heat pump. It heats 114 apartments then pumps the cooled water back into the cooling network.
It's a good idea to increase efficacy even more. This is also why we want to continue expanding these networks, Dworschak said. These combined cooling and heating networks are especially useful in temperate climates such as Germany, where there is potential for convergence of cooling and heating needs. When waste heat from the cooling system is used for example by a heat pump.
The building's insulation significantly reduces cooling needs
However, the most important factor for effective cooling is the building's thermal insulation, explains Wolfgang Hasper from the Passive House Institute in Darmstadt. The independent research institute calculates the energy consumption of buildings, organizes conferences, and trains architects around the world in energy-efficient design.
If buildings have well-insulated facades and roofs, double- or triple-glazed windows, good shading and smart ventilation, “then heat from the outside won't seep in,” Hasper said. Well-insulated buildings require up to 10 times less cooling energy than buildings with lots of glass and no roofing or insulation. Hasper says that if insulated apartments in warmer regions were effectively equipped with decentralized air conditioning systems, this would result in significant electricity savings.
Insulation is a good alternative to district cooling networks because homeowners can install it themselves whenever they want without having to wait for the district cooling network to open, he added. wide where they live. Additionally, he adds, insulation and cooling technology can often be used in conjunction with photovoltaics, especially in countries with hot climates.
When power demand for cooling purposes rises, solar plants can generate a lot of energy because there is abundant sunshine available , Hasper said. There is a good correlation between supply and demand. A good match.
