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Free Cooling for a 4-star city hotel

The “Wilhelmshof” is a four-star hotel in Vienna that focuses on sustainability. Since 2008, the hotel’s DHW preparation has been supported by 156 m2 of thermal solar panels – the biggest of all hotels in Vienna.

This hotel with 102 rooms has been reducing its energy demands through various measures over the years. Now, the gas heating system was to be replaced by a more sustainable option.

Due to the pandemic, the quick decision to begin with planned constructions sooner has been made, making the best of the unfortunate situation. The biggest source of energy is now ground water, used as a source of heat for the water-water heat pump, as well as the “free cooling” concept. Basis of this kind of room cooling is a free, natural “source of coldness” such as ground water. Fan coils are used for the decentralized cooling of rooms.

Three cold reservoirs with a capacity of 2,000 litres each serve as a buffer. In the sunny season, the solar thermal plant provides a majority of the required heat and is now supported by the new 140 kW ground water heat pump. In total, six 1,000-liter cylinders, cooling and heating request, the solar plant and the regulation of the hotel rooms are controlled by 37 freely programmable controllers of the x2 serie



  • 156 m² solar thermal
  • 140 kW groundwater heat pump
  • 1 gas boiler for peak loads
  • 3x 1000 litre buffer storage
  • 3x 1000 litre DHW storage tank
  • 3x 2000 litre cold buffer
  • Heating circuit via panel heating and radiators
  • Cooling circuit via fan coils

This project was realised by: