District cooling supply line for Rudolfinerhaus

The summers are getting hotter and hotter – not just in Austria. Providing adequate cooling for buildings is thus becoming increasingly important. One environmentally friendly and cost-effective option is district cooling.

District cooling is the cooling equivalent of the much more widely-known concept of district heating and involves supplying buildings with water chilled in cooling plants by means of environmentally friendly absorption refrigerators.

These refrigerators are powered by existing waste heat, such as the heat generated by waste incineration plants. The absorption refrigerators are used to cool water down to approximately 6 - 7° C. The chilled water is supplied to customers via insulated pipelines and piped into cooling ceilings to provide air conditioning. After this cooling process, the now heated water is piped back to the cooling plant and fed back into the cycle.

Wiener Netze GmbH is planning to promote the expansion of district cooling on an extensive scale in the next few years.  

In July 2019, following a best bid process, Wiener Netze GmbH commissioned the Fernkälte WIBEBA - Integral consortium to act as general contractor for the construction of a district cooling pipeline to the Rudolfinerhaus private clinic.

The total order value was approximately 2.9 million euros.

A new pipe route was to be constructed, running from the existing pipeline in Heiligenstädter Lände to the Rudolfinerhaus to connect the private clinic to the supply network. In addition to the construction work, the contract also included all the pipe-laying services. The project consisted of three construction sections: “Hofzeile”, “Wertheimsteinpark” and “Krottenbachkanal”.

Due to the short construction period, which was subject to contractual delay penalties, allocated to the “Hofzeile” section, where several schools and embassies are located, the PORR subsidiary Kraft & Wärme Rohr- und Anlagentechnik GmbH was brought on board as subcontractor. The district cooling pipe was to be constructed in plastic, a first in Vienna for a project of this size.

A pre-insulated plastic pipe with a factory-insulated plastic sheath pipe in the dimensions DA 280 PE/KMR 400 was used for the supply flow and an uninsulated plastic pipe in the dimensions DA 280 PE for the return flow. In the Krottenbachkanal sewer, factory PE-coated steel pipes with DN 200 were used for both the supply and return flow.

Before work in the Wertheimsteinpark could begin, a 1,400m² access road had to be built so that the spoil and backfill material could be removed from and the pipes delivered to the site. This necessitated removing a layer of humus about 0.30m thick, which was stored to one side of the road.

A layer of bonded fabric was placed on top of the subgrade and covered with recycled material up to the desired level. Temporary fencing had to be set up to protect all the trees along the route.

In the course of the excavation work, the roots that extended into the pipe trench were laid bare manually and shielded under the supervision of Wiener Stadtgärten.

After completion of the pipe trenches with a route length of approximately 432m, the uninsulated plastic pipe and the factory insulated plastic sheath pipe were laid and the joints welded. A pressure test with water was performed here as well, to ensure that the pipeline was leak-proof. The pipeline was subsequently covered with sand.

Under the paved surfaces, the trenches were filled with self-compacting material and temporarily sealed with hot mix. In the grassy areas, the trenches were filled with graded replacement material and the last 0.30m were backfilled with screened humus soil. To complete the work in this construction section, the temporary site road was dismantled and the humus that had been stored by the roadside was replaced.

Approximately 2,260m of DN 100 cable conduits were laid in the Hofzeile and Wertheimsteinpark sections. In addition, 21 cable ducts were manufactured from prefabricated parts.