The project will replace 68.5 km of old, damaged pipes in Zagreb’s district-heating system, out of a total length of 227.3 km. This will reduce heat and water losses and contribute to a reliable, efficient network that is compatible with heat generation from renewable sources in future. The project will help meet EU and national energy goals.
Upgrades to Zagreb’s district-heating system to save water and cut energy loss
- 13 January 2021
The sections to be replaced have the largest number of leaks in the system, and nearly half are over 40 years old. The work will ensure that network operator HEP-Toplinarstvo remains competitive at a time when gas and electricity prices are relatively low.
Benefitting the urban population
The district-heating network supplies 91 562 homes and 4 322 businesses and serves about one-third of the city’s population (270 000 people out of 800 000). In 2017, a total of 1.2 TWh in heat energy was supplied to customers. The water is heated using natural gas (93 %) and oil (7 %).
The project will be implemented in 17 urban areas of Zagreb: Siget, Sopot, Trnsko, Utrine, Donji grad, Folnegovićevo naselje, Kruge, Vrbik, Savica, Borovje, Sigečica, Gajevo Staglišće, Jarun, Srednjaci, Cvjetno naselje, Trešnjevka and Voltino.
50-year lifetime
The old steel pipes lay in underground concrete channels and are insulated with mineral wool wrapped in paper coated with water-repellent bitumen. This insulation has become worn and damaged, due to infiltration of surface water. The water often contains dissolved salt and other harmful substances which have corroded the pipes.
The new hot-water pipes, which will have the same diameter, are also steel, insulated with polyurethane and cased in polyethylene, which is common in European district-heating networks. They will be equipped with failure-detection alarms.
These pipes will be resistant to fouling and corrosion and have an expected lifetime of over 50 years. The water in the system is already of good quality as it is softened and treated to remove corrosive gases, oxygen and carbon dioxide, which helps protect the pipes from wear.
Reducing heat and water loss
The poor state of the pipes leads to heat and water losses and requires a significant number of repairs. In 2017, 15.2 % of the total heat produced was lost compared to less than 10 % expected from modern district-heating networks.
A total of 1.2 million m3 of water was lost from the system which meant the water in the system had to be replaced 46 times in 2017. In comparison, in modern networks, the water is replaced about once a year.
Each year, on average, a total of 75 repairs to fix leaks have to be carried out, or 0.32 repairs/km/year. In the part of the network covered by the project, this figure is 0.49. Typical West European networks require 0.1 repairs/km/year.
By 2023, it is calculated that the project will have reduced the number of repair jobs by 90 % compared with 2018. Total heat losses will cut by 28 % and water losses by 47.4 %.
Sustainable development
The project aims to improve the energy efficiency and security of Zagreb’s district-heating system. Benefits will include lower operation and maintenance costs and reduced emissions of carbon and nitrogen oxides. This will benefit the health of residents while less heat loss will reduce the consumption of natural gas.
The project is in line with the Sustainable Development Goals at European and national levels and for HEP-Toplinarstvo. Zagreb’s district-heating system is energy efficient, as defined by the EU’s Energy Efficiency Directive, as over 75 % of the heat it supplies comes from cogeneration. Two, high-efficiency cogeneration plants supply the heat for the network.
Total investment and EU funding
Total investment for the project “The revitalisation of district heating network in the City of Zagreb” is EUR 94 363 789, with the EU’s ERDF Fund contributing EUR 55 460 526 through the “Competitiveness and Cohesion” Operational Programme for the 2014-2020 programming period. The investment falls under the priority “Promoting Energy Efficiency and Renewable Energy Sources”.