One of the problems that affects the management of large buildings is energy consumption. Wireless sensor networks are presented here as a great ally for the optimization of energy consumption. Thanks to the integration of temperature, lighting, humidity, air quality or gas sensors, combined with different actuators that can monitor and regulate the level of work of energy-consuming devices, and software management and analysis, energy consumption in large buildings is significantly reduced without decreasing the availability and effectiveness of resources. Hotels are a kind of ideal building to implement these systems. Nebusens has launched a pilot in a hotel, so energy consumption points can be monitored (HVAC, boilers, etc.), thanks to the implementation of the sensors that are integrated into its platform n-Core using its management software Polaris. Thus, the energy consumption has been reduced by up to 35% since the introduction of the pilot without any decrease in quality of service.