By Niels Vilstrup, Project Manager, Energy, COWI
The demand for district cooling is on the rise. This also counts for oil and gas rich Qatar where part of the cooling in the upcoming Doha Metro will be delivered by a district cooling system. COWI is the project leader on the challenging task.
The Doha Metro project owner, Qatar Rail, has chosen to change part of the planned decentralized cooling with dry air cooled chillers at each station in favor of a more energy efficient district cooling system in the upcoming Doha Metro, where some 130 COWI engineers are leading the design work on the Red Line North Underground consisting of two tunnels of each 13 kilometers and 7 underground stations. A COWI led design Joint Venture is responsible for designing all civil works, MEP (mechanical, electrical and plumbing) and architectural works on the Red Line North Underground, a central part of the Doha Metro system. The advantage of district cooling is that is it is far more energy efficient and much less space consuming than decentralized cooling with dry air cooled chillers at each station. With desert temperatures well over 50° C, the Doha Metro's cooling system is decisive for the operation, safety and comfort of the metro stations as well as inside the tunnels if a train breaks down. Cooling more with less The demand for district cooling is rising around the world due to urbanisation, climate change and a need for more energy efficient solutions. In general, a bigger district cooling system can be up to 40-50%more energy efficient than a decentralized cooling system.
COWI Design Manager, Niels Vilstrup, in a section of a metro tunnel placed outside RLNU site office in Doha and with Doha City Center in the background
The chilled water pipes are supposed to be routed inside the metro tunnels which are mainly fitted for the metro train and the related equipment. This has increased the challenges in the project a lot due to space constrains inside the tunnels. The first intensions were to have both the chilled water supply line and return line in one tunnel. During the concept design it became clear that there was only space to have the supply line in one tunnel and the return line in the other tunnel. On top of that, the tunnel concrete walls in the Doha Metro are not designed to support heavy waterfilled 18” cooling pipes needed for a district cooling system. Moreover, the tunnels have many curves and height differences putting high demands on the flexibility of the pipes and especially on the design of pipe supports.
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