From Deployment to Operation: A Reproducible IoT Testbed for Smart-Building HVAC with OTA and Observability
Smart-building research increasingly requires IoT platforms that support reproducible deployment and long-term operation under real conditions. This paper presents a field-operable and reproducible IoT testbed for smart-building HVAC, grounded in an architecture aligned with ISO/IEC 30141 and designed for zero-touch onboarding, fleet-wide Over-The-Air (OTA) lifecycle management, and end-to-end observability. The architecture integrates ESP32-based devices running FreeRTOS, multi-protocol communication using MQTT and CoAP, and a lightweight containerized backend with time-series persistence and monitoring.The testbed was deployed in a university laboratory, where a rule-based HVAC control strategy reduced monthly energy consumption from 101.68 to 45.04 kWh (55.7%) while maintaining thermal comfort. Controlled experiments further evaluate protocol trade-offs, quantifying MQTT QoS impacts on actuation latency and comparing MQTT and CoAP for continuous telemetry under constrained conditions. In addition, the architecture enables progressive edge intelligence through data-driven model deployment without structural changes.Rather than proposing new protocols or control algorithms, this work contributes a standards-aligned, observable, and evolvable IoT testbed, together with empirical evidence and practical design insights for field-oriented smart-building research.