The basis of district heating in Ljubljana is transmitted by the hotwater system. This is a two-pipe system of heating, in which heat is chemically prepared, demineralized and degasified hot water. Hot water characteristic in the network is the following: pH value from 9 to 10, common hardness from 0.2 to 0.5øN, phosphates to 1 mg/l, silicates from 0.5 to 0.8 mg/l, hydrazine from 0.1 to 0.2 5 mg/l, oxide to 0.25 mg/l, electric conductivity from 50 to 70 AS/cm and common iron to 0.5 mg/l. The supply temperature depends on the outdoor air temperature and is from 70-130 øC. Return temperature depends on internal heating installations of consumers. This temperature is desired to be as low as possible thus contributing to the improved output of the entire system.
The lowest temperature of outdoor air at which JP Energetika can still assure the desired room temperature is 20øC. District heating network operates 24 hours a day nonstop during the whole year with the exception of short breaks (announced in advance) due to maintenance works. Nominal pressure of hot-water network is 16 bar.
Such conditions of operation are assured in the both heating stations where water is heated up to the suitable temperature and then transferred to the network by means of pumps. Heat production for hot-water system started in 1961; the year 1966 saw the operation of Toplarna Ljubljana. Toplarna Siska started production in 1971.
Heat in steam system is transferred by superheated water steam, with which mostly factories using it for technological needs are supplied. Steam production started in 1968 in Toplarna Ljubljana, and in 1973 in Toplarna Siska.