The SUSTIE test facility was completed in 2020, and it facilitates to the development of energy-conservation technologies while contributing to the realization of more comfortable and energy-efficient indoor environments. The facility achieved the top rank of energy performance certification "Building-Housing Energy-efficiency Labeling System (BELS)" and wellness-office certification "Comprehensive Assessment System for Built Environment Efficiency-Wellness Office (CASBEE-WO)" in Japan.To accelerate research and evaluation, we propose an efficient Internet-of-things (IoT) platform called the SUSTIE Core Engine. The platform gathers data in real time, stores both design data and time-series data with coordinates, and act as simulation interface to satisfy three requirements of an IoT platform for smart facilities: an architecture that allows adding / removing functions without stopping operation, data management features for time-series / coordinates data, and common interface for simulations / controls. We implement the platform which covers the requirements to on-site system in the test facility, and evaluate the gateway, spatiotemporal database, and simulation interface. Our platform showed that it satisfies the three functional requirements of IoT platforms. Furthermore, it was shown that the database can obtain sufficient demonstrated for practical use.