The diameters of the piping can range from DN 150 to DN 900 for cooling and, similarly, from DN 80 to DN 450 for heating.
In order to understand the scale of the network, a 12-meter pipe of DN 800 weighs about 2.77 tons and holds almost 6,000 litres of water.
The pipes used are thermally pre-insulated and are supplied by the factory already heat insulated. This insulation is carried out by means of an automatic continuous injection process.
Each pipe is made up of several layers, from the inside out, and include:
A steel pipe for transporting the fluid.
A layer of insulation based on rigid polyurethane foam.
An outer coating of high-density polyethylene.
The four pipes are laid side by side in a single trench. On one side of the trench is the cold-water supply pipe and then, in that order, the cold water return pipe, the hot water return pipe and, finally, the hot water supply pipe.
In the design of the network, special attention is paid to the phenomena of thermal expansion and fatigue, by means of complex calculations for this purpose.
Alternatively, the pipes can be arranged inside service galleries, fixed by means of metallic supports specially designed to avoid damaging the insulation of the pipes or generating thermal bridges (neoprene layers, plastic cradles, etc.). In its design, special care is taken with the maximum distances between supports and the location of the fixed points.
The installation of the network is completed with mechanical cleaning and chemical cleaning to prevent internal corrosion as well as hydraulic and watertightness tests of 16 bars for 24 hours. Various quality controls of welding and civil works are also carried out prior to commissioning.
In the same trench through which the hot and cold-water pipes run, there are three 50 mm diameter polyethylene pipes (or a tri-tube) for the passage of fiber optic cables that allow monitoring of the energy delivery points to the customers from the power plants.
There is also a leak detection system based on the detection of the variation of the electrical resistance of a conductor cable embedded inside the polyurethane layer of the conduits. This system makes it possible to detect any humidity indicative of a defect in the thermal insulation, not so much due to water leaks from inside the network as to leaks from outside it.
