This document describes the Proof of Concept carried out in Project PHOENIX. The document covers the actions and measures that were implemented in terms of hardware, with the solutions that were adopted as well as the implementations in terms of software. In implementing the Phoenix platform at the PoC pilot, it became evident that the intermediate components between the sensors/gateways and the services are of great importance and that those layers are the basis of interoperability. This aspect is therefore highlighted in this document. The lessons learnt from the PoC are many, but in general, we have seen that (i) each building has specific characteristics that need to be assessed and (ii) the person-hours of specialized personnel is expensive and difficult to find whereas hardware solutions can be more cost effective and easier to implement. In addition, we have seen that integrating the BMSs is key for the proliferation of smart buildings.