Efficient cooling is not only needed in the hot south

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Published on Wednesday, 18 July 2012 10:35

Written by Silke Thole

Cooling and air conditioning are frequently only associated with the hotter countries of Europe. It is true that a number of the CONCERTO cities in the hotter regions of Europe are focusing on energy-efficient cooling, however, similar projects are also to be found in the north of Europe. Sorption-chilling processes are typically used in both north and south to obtain cool temperatures from heat.

Cooling and air conditioning are frequently only associated with the hotter countries of Europe. It is true that a number of the CONCERTO cities in the hotter regions of Europe are focusing on energy-efficient cooling, however, similar projects are also to be found in the north of Europe. Sorption-chilling processes are typically used in both north and south to obtain cool temperatures from heat. An example is the two towns of Cerdanyola del Vallès in Spain and Ostfildern in Germany, both members of the CONCERTO Policity project.
In the ST-4 cogeneration power plant in Cerdanyola del Vallès three highly-efficient cogeneration units with an installed capacity of 3.35 megawatts generate electricity and heat simultaneously, with part of the heat used in summer to generate cooling energy. The town on the outskirts of Barcelona currently operates two absorption chillers with a maximum cooling capacity of 3 and 5 megawatts. Two more are set to join these in the future. A further component of cooling energy supplies is an underground chilled water storage tank of 3,700 m3, which acts as a buffer to meet higher cooling demands during peak loads.
The power plant in Cerdanyola del Vallès is gas fired, in Ostfildern, in contrast, the heat required for the absorption chilling plant is delivered by a biomass OCR cogeneration plant. Cogeneration plants make particularly efficient use of the energy. Regardless of whether it is a large combined heat and power plant or a mini CHP unit in a single-family dwelling, the functional principle remains the same: a combustion engine powers a generator, which in turn produces electrical power. The exhaust heat created in the process is used for heating or – as is the case in Cerdanyola del Vallès and Ostfildern – for cooling. In this way over 90 percent of the primary energy employed is utilised. If electricity and heat or cooling energy are generated separately in the standard manner, the overall efficiency amounts to merely between 60 and 70 percent, one third of the energy employed is blown out unused.
In both Cerdanyola and Ostfildern the primary consumers of the cooling energy produced - which is distributed via a district cooling network - are office buildings. In the CONCERTO town of Växjö, too, the high concentration of office and commercial buildings results in a high cooling requirement which justifies the construction of a district cooling network. In Geneva the waters of Lake Geneva are used as a source of energy, with a constant temperature of eight degrees Celsius.
On the other side, none of the southern European cities implemented cooling systems in residential buildings, whereas Lyon in France and Heerlen in the Netherlands did so with “free cooling“ concepts. As with Geneva, Herleen used temperate water as a source of energy. This comes from the galleries and shafts of the former Oranje Nassau coal mine. Depending on the pumping depth, the temperature of the water collected in the mine varies in level. The 28-degree water at a depth of around 700 metres is used as an energy source for heat pumps, with the 14-16-degree water for cooling coming from layers that are situated closer to the surface. In this way it is now possible to efficiently provide 170 homes, a supermarket, a cultural centre, a school with kindergarten and a small industrial estate with heat and cooling energy.
The examples show: it is not only in the warmer countries of Europe that significant energy can be saved through efficient cooling concepts. Which concept is the right one is largely determined by local conditions. The CONCERTO projects offer numerous examples of how these conditions can be utilised. The mine water plant in Herleen is a role model for other regions with abandoned mines, for example, cogeneration as an economic solution when the use of groundwater, geothermal energy or the sun is not an option.
In countries with extensive sunlight the use of solar heat plants to generate heat and cooling energy is a logical choice. Consequently, a solar heat power plant is also planned for Cerdanyola del Vallès, in addition to the gas-fired power plant. “ST-2”, which is also set to use wood gasification energy, is due to come on line in mid June 2013. The lower sunshine levels in the north of Europe are not an exclusion criterion for the use of solar heat energy for cooling, however. The Finnish town of Lapua, for example, has integrated solar-driven sorption cooling.