Fernkälteversorgungsleitung Privatklinik Rudolfinerhaus

In 2019, Viennese utility provider Wiener Netze GmbH held a best-bidder tender procedure for the installation of a new district cooling pipeline to the Rudolfinerhaus private hospital. The contract, worth approximately 2.9 million euros, was awarded in July 2019: the district cooling consortium Fernkälte WIBEBA – Integral was named as general contractor. The project involved creating a new route along Heiligenstädter Lände, a street in Vienna’s 19^th district, to link to an existing pipeline to the Rudolfinerhaus. As well as the master building services, the contract covered all the pipe laying work – which had to be done in close coordination with Vienna’s sewage company, Wien Kanal, and the city’s Parks & Gardens department, Wiener Stadtgärten.

The project comprised three construction stages: Hofzeile, Wertheimstein park and Krottenbach sewer. Hofzeile is a street where a number of schools and embassies are located. This necessitated a very short construction period, and any delays were subject to a contractual penalty. To ensure the deadline could be met, an experienced subcontractor was brought on board: PORR subsidiary Kraft & Wärme Rohr- und Anlagentechnik GmbH. The district cooling pipeline was designed using plastic pipes – a first in Vienna for a project of this scale.

The supply pipeline was implemented as a pre-insulated plastic pipeline with a factory-insulated plastic sleeve; dimensions DA 280 PE/KMR 400. For the return flow, uninsulated plastic pipe was used, with dimensions DA 280 PE. A DN 200 steel pipe, coated in PE in the factory, was installed in the Krottenbach sewer section.

Construction section 1: Hofzeile.

The district administration required that the 516m pipe route be completed during the school holidays, and the employer reinforced the deadline with a stiff contractual penalty. Exacerbating the very tight deadline, the consortium had to work in extremely cramped spatial conditions. A traffic lane at least 2.5m wide had to be kept available at all times, to ensure that the parking spaces and 24h access needed by the embassies located in the area remained available.

Once the trenches had been constructed, two parallel pipelines – for the supply and return flows – were laid on Styrodur underlay. A water pressure test was then carried out to check that the welds were watertight. When the pipe laying was complete, the pipes were covered in sand, the trenches were filled with self-compacting material, and the surface was temporarily sealed with hot-mix asphalt.

Construction section 2: Wertheimstein park.

Before starting work in Wertheimsteinpark, a large access road, covering an area of 1,400m², had to be built; this would be used to transport filler material, deliver the pipes, and take away the spoil. To create the road, the top layer of topsoil – around 30cm of humus – was removed and stored nearby; a layer of felt was then installed and covered with recycled material to bring the route up to the required height. All the trees along the route had to be protected with temporary fencing. Any roots found as the pipeline trenches were being dug were exposed manually and protected, under the supervision of the Vienna Parks & Gardens department.

Once the 432m long pipe trenches were complete, the uninsulated plastic pipe and the factory-insulated plastic sleeve was installed and the joints were welded. Once again, a water pressure test was carried out to ensure that the pipes were watertight before they were covered with sand.

Next, the trenches beneath the paved areas were backfilled with self-compacting material and temporarily sealed with hot-mix asphalt. Beneath the green areas, the trenches were backfilled with graded replacement filler and the top 30cm were filled with sieved humus. Finally, the teams completed the construction stage by dismantling the temporary access road and replacing the saved humus. Around 2,260m of DN 100 prefabricated cable conduits and 21 prefabricated cable ducts were installed in the Hofzeile and Wertheimstein park construction sections.

Construction section 3: Krottenbach sewer.

Work in the Wertheimsteinpark section was still underway when work began in the Krottenbach sewer – a 3.2m x 2.5m brick sewer. Before Kraft&Wärme and Integral could start work laying the pipes in the sewer, WIBEBA dismantled the construction pit and extended the brick arch to 6.5m x 2.5m. A dedicated stairwell was built to provide safe access to the Krottenbach Sewer. In the sewer itself, sleeved DN 200 PE steel pipes were laid on brackets coated in coal tar epoxy along a 2m x 294m section.

All work in the sewer had to be coordinated in daily discussions with Vienna’s sewage company, Wien Kanal. A safety officer had to be present above ground at all times to ensure prompt action could be taken if any flooding occurred in the sewer. When it rained heavily, work had to stop, since the sewer would flood. All workers were required to wear a multi-gas monitor and a self-contained self-rescue device.

Once the steel pipe had been laid and welded, not only was the water pressure test carried out, but in addition 10% of the weld seams were subjected to x-ray inspection to verify that there were no welding defects. As soon as the pipe had been declared properly watertight, it was connected to the existing system.

Finishing work.

The final step involved backfilling the pipelines along their entire length and preparing them for operation. A high-grade steel mesh housing was installed around the steel pipelines to protect them against damage. The stairwell was then removed, the sewer vault sealed with prefabricated concrete parts, and the construction pit backfilled.