Wien Energie reports that on heat days around 35 °C, its district cooling requirement rises by up to 60 percent compared with average summer days. The highest load peaks typically occur between 11:00 and 16:00, the company told APA.
But the system runs at full tilt not only by day: warm nights also drive up demand, because the heated cityscape cools less after sunset. This is especially evident during so-called tropical nights—when temperatures do not fall below 20 °C. This year saw the first tropical night in the first week of June; Vienna’s city center recorded 53 such nights in 2024.
€90 Million Investment Planned
Wien Energie will invest €90 million over the next five years in its district cooling network. Its first central plant opened in 2009 at the Spittelau waste-to-energy facility, utilizing combustion waste heat—available even in summer—to power large chillers.
Today there are seven district-cooling plants in Vienna tied into a network, supplied either by waste heat or green electricity. An eighth plant will come online this year at the Medical University campus. Over the years, the network’s insulated pipelines have grown to 30 kilometers, carrying water chilled to around 5–6 °C to customers across the city.
Compared with conventional air-conditioning units, district cooling cuts CO₂ emissions by 50 percent and avoids the secondary waste heat typical of split-unit systems.
