Many new structures incorporate energy management systems such as intelligent lighting, HVAC control systems that allow profiling the energy spent in the building. However, a much larger portion of existing buildings do not have any energy monitoring retrofitted. WSNs represent an appropriate solution to allow energy monitoring in such buildings. For example this would allow quantifying and understanding how the energy is spent throughout the building to better direct investment for energy-efficient solutions. The first step in order to reduce the energy consumption in a building is to measure how and where the energy is spent. As each building is unique, we need to define how data gathering on energy consumption can be obtained. This should clearly reflect how energy is spent in relation to how an infrastructure is being used: