Background The increasing complexity of building systems, such as HVAC (Heating, Ventilation, and Air Conditioning), lighting, and energy management, has exacerbated interoperability challenges. Diverse communication protocols and data formats hinder seamless integration, affecting optimal building performance and energy efficiency. Demand Response (DR) programs, which adjust energy use based on grid signals, are particularly impacted by these issues. Methods This study proposes an ontology-based approach to address interoperability in DR programs, using the DEDALUS project as a case study. The DEDALUS project aims to enable large-scale DR participation and adapt to various energy scenarios. A multi-level framework was developed, emphasizing foundational, structural, and semantic interoperability. The foundational layer employs the Demand Response Control Ontology (dCO), expanded with DR-specific entities. Integrating established ontologies, such as Smart Appliances REFerence ontology (SAREF), Open Automated Demand Response (OpenADR), and Brick schema, ensures consistency and expedites development. The FIWARE Next Generation Service Interface-Linked Data (NGSI-LD) standard enhances system compatibility across applications and services. Results The integration of ontologies within the DEDALUS framework standardizes data models, ensuring semantic consistency and facilitating effective communication between building systems and the grid. By leveraging ontologies like dCO, SAREF, and Brick, the project enhances data interoperability and reduces development complexity. The use of FIWARE NGSI-LD for context data management ensures that systems remain compatible and can seamlessly exchange data, improving overall system efficiency and responsiveness. Conclusions The study highlights that semantic interoperability is essential for successful DR programs. Standardizing data models and protocols enhances system communication and efficiency. This work underscores the importance of ontology-based frameworks and open standards, such as FIWARE, to promote innovation, reduce energy consumption, and advance sustainable building management.