Production of district cooling
District cooling is eco-efficient urban energy at its best. The fundamental idea of district cooling is to use local resources that otherwise would be wasted. However, about 80 per cent of yearly district cooling production in Helsinki is based on resources which otherwise would be wasted. District cooling uses largely renewable energy sources such as seawater. The current share of renewable is about 60 %. Due to large share of renewable and utilization of resources that otherwise would be wasted, CO2 and other greenhouse gas emissions of district cooling are less than 20 % compared to building specific cooling systems.
Forms of production
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Free cooling using seawater
Free cooling produces district cooling from cold sea water between November and May, when its temperature is below 8°C. The cooling is produced direct from sea water whenever possible -
Absorption cooling
The absorption technique is employed to produce district cooling using thermal energy that is otherwise wasted in energy generation. The absorption machinery operates in summertime, when sea water is too warm for free cooling. -
Heat pump plant
A heat pump is used to recover thermal energy obtained from district cooling. The heat is transferred to the district heating network for heating buildings and domestic hot water in Helsinki.
District cooling in Helsingin Energia
Heat produced in Helsingin Energia’s CHP plant is not useful as district heat in the summer. That is when district cooling energy is produced by absorption technology using the otherwise unutilised heat.
In the winter, district cooling is produced using cold seawater. Seawater is an inexhaustible source of cooling energy. In the winter the process is very simple since, in addition to heat exchangers and pumps, no other equipment is needed.
During the summer cooling energy is mainly produced by absorption cooling plants. The fuel of absorption plants is surplus heat from electricity production.
Another production method is based on utilisation of purified waste water in the Katri Vala heat pump plant. Heat pumps are designed to produce district heat and district cooling in same process.
A district cooling system has a considerably longer lifetime than building-specific cooling systems. The service life of an absorption cooling plant is approx. 30 to 50 years, while that of an equivalent building-specific compressor system is only 15 to 20 years. Once a district cooling system has been built, its life cycle is more than 200 years.