CLIMIFY proposes a digital, vendor agnostic solution for ad-hoc upgrades of the existing building stock. The solution includes: 1. Third-parties’ IoT sensors to monitor rooms’ indoor climate, occupancy, window position, and energy usage; 2. third-parties’ actuators, such as window-motors, motorized window shutters and blinds, smart thermostats, etc. 3. FeedMe, our dedicated, CLIMIFY-proprietary, two-ways live-feedback mobile app, to gather feedback from occupants, and to provide feedback to occupants, while tracking their position within the built environment, and 4. climify.com, our web-platform: here, monitored data and live feedbacks get collected, stored, and evaluated, while control signals are generated and forwarded to actuators and to the BMS. Our user-friendly web-platform is designed to ensure easy and correct access and visualization to monitoring data to: 1. occupants, such as pupils, teachers, employees, and tenants, 2. buildings’ and organizations’ managers, such as facility managers, municipalities and property owners. In the back-end of the platform, our AI uses the monitored data to generate a digital twin of each building. Here, based on measured data, occupants’ feedbacks and weather forecast, our model predictive control engine generates the control signals of the available actuators. Also, our AI continuously analyzes window positions, together with occupancy, temperature, relative humidity and CO2 levels in each room, and provides constructive feedback to the occupants, for example on when to make use of natural ventilation and when to close windows again. To track occupants in public buildings, we install Bluetooth low energy beacons and execute a fingerprinting of the building. Occupants using FeedMe will be tracked and can provide live-feedback on indoor conditions, without having to specify the location they are in. In this way, we know occupancy levels and can predict those, and control buildings according to ACTUAL NEEDS. A different version of FeedMe, not tracking occupants, is used in residential houses.