This paper proposes an innovative strategy to optimize the energy metering in large and energy-consuming plants such as industrial flour mills. The proposed solution deals with ISO 50001 implementation which represents a critical challenge for many companies because the benefits due to improvements in energy management could be potentially canceled by the costs of an Energy Management System (EnMS). In particular, the Key Performance Indexes (KPIs) monitoring is a crucial activity for several reasons: it is one of the early activities, it affects the measurement quality of KPIs and it deeply impacts the EnMS requirements and, consequently, the investment valuations. The proposed strategy supports the energy managers in the design of the energy monitoring system suggesting the points of the electrical network to be equipped with sensors and monitored. Moreover, the paper describes the results carried out in a real-world application: the energy sensor network of a 1.2MW flour mill plant sited in Italy has been designed and implemented with the proposed innovative solution.