A Study of the Capabilities of Building Management System APIs and the Limitations of Their Practical Usage

Access to Building Management Systems (BMS) and their data is essential for developing applications and conducting research aimed at improving building energy efficiency. The management layer of BMS includes Human-Machine Interfaces (HMIs), such as building management software, and in some cases Human-Device Interfaces (HDIs), which enable direct interaction with individual devices (e.g., thermostats). These interfaces are accessible via Application Programming Interfaces (APIs) that facilitate programmatic access to subsystems such as HVAC, lighting, and security. However, vendor-specific APIs present heterogeneous representations that pose significant interoperability challenges. To address this, we analyse APIs from five major BMS vendors—Siemens, Honeywell, Schneider Electric, Johnson Controls, and Delta Controls—and categorise their capabilities into 12 feature groups. We go beyond descriptive analysis by evaluating these APIs against 85 common applications, providing a systematic framework to measure their suitability for real-world building solutions. Recognising the role of semantic ontologies in interoperability, we further examine how Project Haystack and Brick can represent the data exposed by BMS APIs within these feature groups, highlighting strengths and gaps in existing approaches. Finally, we demonstrate a practical use case that leverages Siemens Desigo APIs to instantiate standardised models through a metamodel. This metamodel supports control algorithm integration, enabling energy-efficient building operation. Our work advances the state of the art by empirically linking BMS API capabilities to application requirements, semantic models, and practical control integration—providing both researchers and practitioners with actionable insights for deploying interoperable building solutions.