Telecommunications are expected to reduce the energetic impact of human society through dematerialization. But in addition to their utilization consumption, the ICT equipments are responsible of energy consumption for their fabrication. To assess as precisely as possible their consumption and the gain compared to physical services, we use a new modular and open method intended to reduce errors and highlight possible improvements. The lithography phase of chips manufactured from extrapure silicon wafers is responsible for about 70% of the consumption of chips fabrication. The main elements of this phase are the tools, which make the operations, and the air circuit, which cleans the air and control its levels of temperature and humidity 24h/24. This element is deeply analyzed in this paper, as a key module of the method which can be reused for other studies. Many parameters take part in the air circuit consumption, particularly the climate of the place where the factory is built, the class of the clean room and the amount of particles emitted. We try to put them ahead to understand this consumption and to know how to improve the energy efficiency.