Operating Principle

District heat is produced in combined heat and power (CHP) plants or in heating plants. Customers receive heat from the hot water circulating in the district heating network. District heat is available around the clock throughout the year.

The temperature of district heating water supplied to the customer varies between 65 and 115 ºC, depending on the weather. The temperature is at its lowest in the summer when heat is needed only for hot tap water. The temperature of water returning from customers to the production plants ranges between 40 and 60 ºC.

When a customer joins the district heating network, a heat distribution centre is installed in the customer’s property. The operation of the heat distribution centre is reliable with a minimal need for maintenance.  In single-family houses, the heat distribution centre may be located in a cupboard to take as little room as possible.

Heat is conducted to customers as hot water in a closed district heating network consisting of two pipes. Hot water is conducted to the property’s distribution centre, from where it releases heat into the customers’ heating network and for the production of hot tap water with the aid of heat exchangers. Heat is used in houses for the heating of rooms and hot tap water, as well as for ventilation. Once cooled down, the water of the district heating network returns to the production plant for reheating. District heating water does not circulate in the heating networks of buildings.

District heating water is treated to remove mechanical impurities and oxygen and to prevent corrosion inside the pipelines. The water is also often dyed in order to locate leaks or damages.  The colorant that turns the water slightly green is not hazardous to health or the environment.

District heat is produced in combined heat and power (CHP) plants or in heating plants. District heating fuels include natural gas, coal, peat, and increasingly wood and other renewable energy sources, such as biogas. Almost 80% of district heating is obtained from heating plants producing heat and electricity (CHP, cogeneration), as surplus heat from industry or from biogas combustion in landfills. In small population centres, these heat sources are often unavailable. In such a case, district heat is produced in heating plants producing heat only, often using wood and other renewable fuels.

The reliability of the supply of district heat is almost 100%. District heating networks are usually looped, which enables customers’ heat supply from more than one supply source.