Energy consumption

The main energy-consuming devices in a tunnel during normal operation are: 

• Lighting;
• Sanitary ventilation;
• Safety devices (signalling, closed circuit television CCTV, etc.);
• Pumping (in subsea tunnels or when there is water seepage).

The respective share of each of these energy-consuming systems varies greatly, depending on the specific characteristics of the tunnel: length, gradient, water ingress, etc. Let us consider, for example, the case of a short tunnel: it will not be ventilated (therefore the ventilation element is removed), but it will be lit with entrance zones covering almost its entire length and, due to its shortness; lighting will be a major energy-consumption factor. In contrast, for very long tunnels, the energy-consumption of lighting will be low compared with the energy-consumption of the ventilation system.

In relation to energy expenditure, the first thing that an operator can do, for any given energy requirement is to play competitors off against each other by consulting several suppliers that provide the kind of electricity to be used (renewable energy). This approach assumes that the installation is optimized in terms of the power installed and the operating times of the various pieces of equipment. 

In effect, we have seen that energy expenditure is closely linked to two factors: the power installed per family of equipment and each family of equipment’s operating time.

For each family of equipment, the installed power is assessed during the study phase and is fixed during the implementation phase. Once the structure is operational, the power can mainly be changed during renovation. At this time, it may be decreased if the regulations haven’t changed and if the energy performance of the replacement equipment has improved. It may be increased if regulations have become stricter (for example: greater smoke extraction capacities). 

Basically, outside of renovations, if an operator wants to reduce its expenditure on electricity, it can only do so by optimizing the operating times of the installed equipment and by monitoring peak hours.