A heatwave at CERN

It's getting hot in Buildings 201 and 860, over-heating even... But no reason to panic! We're talking about the superheated water boilers of CERN's two heating plants, which heat all the buildings on the Meyrin and Prévessin sites.

View of the three boilers and the control centre of the Meyrin heating plant.

CERN's two heating plants each comprise three gas* boilers, with generators of 15 MW in the case of Meyrin and 5 MW in the case of Prévessin. Both inject pressurised water, superheated to 125 degrees, into several kilometres of pipes, 22 km on the Meyrin site and 5 km in Prévessin. "A single boiler is sufficient most of the time but a second kicks in automatically during very cold weather, and a third is there on stand-by," explains Christophe Martel, head of the GS Department section responsible for CERN's heating and air-conditioning systems.

All of CERN's buildings have a sub-station that receives the superheated water from the boilers and makes it available for use in different types of heating systems: hot-air systems in the case of most of the industrial-type halls, and hot-water systems in the office buildings. In the hot-water systems, the water circulates through the radiators at a temperature of between 40 degrees (in the case of recent buildings with good heat insulation) and 80 degrees.

Safety first. "The boilers operate at very high power," explains Christophe Martel, "and the operating rules are obviously very strict for safety reasons." In addition to twice-yearly inspections by the official Swiss body (ASIT – Association Suisse d’Inspection Technique) in Meyrin and the French one (an accredited control office) in Prévessin, the GS Department team conducts daily safety tests and checks the primary operations of the auto control system for each boiler every 72 hours in Meyrin and every 24 hours in Prévessin. "On the French site we plan to add two automatic safety systems that will allow us to perform the checks every 72 hours instead of every 24 hours at present," adds Christophe. “The French control office will have to validate the changes but if all goes well we should be able to implement them by the summer."

The three boilers of the Meyrin heating plant.

Energy savings. The burners of the main boilers on both sides have undergone a number of changes with a view to optimisation. The one on the Prévessin site had to be replaced, in fact, while the one on the Meyrin site was reconfigured. Thanks to these changes, real-time combustion analysis involving constant measurement of the CO, CO₂, O₂, NO and SO₂ concentrations is now possible, so that the burner can be permanently tuned to reduce the flow of gas to the minimum. "Data from all the installations are analysed in real-time," explains Christophe. “Thanks to this, and perfect optimisation, we have been able to reduce power consumption by over 10% when the boilers are at full power.” The heating plants generally only run from September to May, so the GS Department team intends to optimise two other boilers when they are switched off this summer.

by Anaïs Schaeffer