Research and Reviews in Sustainability 2977-8441 Caravel Press 10.5334/rss.9 2025.004 A Review of Energy Efficiency Strategies in Smart Buildings: Integrating Occupant Comfort, HVAC Optimisation, and Building Automation https://orcid.org/0009-0007-0405-9922 OnwehChinedu C. chinedu.onweh2023@my.ntu.ac.uk https://orcid.org/0000-0002-9867-6011 Al-HabaibehAmin amin.al-habaibeh@ntu.ac.uk https://orcid.org/0000-0002-9002-3681 ManuEmmanuel emmanuel.manu@ntu.ac.uk PhD Student, Product Innovation Centre, School of Architecture, Design and Built Environment, Nottingham Trent University, UK Director Product Innovation Centre, School of Architecture, Design and Built Environment, Nottingham Trent University, UK Department of Construction Management, School of Architecture, Design and Built Environment, Nottingham Trent University, UK 29102025 1 48 60 29 October 2025 © 2025 The Author(s). Published by Caravel Press. 2025 This is an open access article under the CC BY 4.0 licence.

The convergence of artificial intelligence and the Internet of Things technologies is transforming how smart buildings balance energy efficiency with occupant comfort. This systematic literature review synthesises research findings published between 2015 and 2025, drawing on 52 peer-reviewed studies alongside 26 additional authoritative standards and high-quality policy reports identified through a structured search across major academic databases, targeted journals, and grey literature. The synthesis examines reported approaches to heating, ventilation, and air conditioning system optimisation, building automation, digital twin technologies, and occupantcentred control strategies, with specific attention to cold climate contexts. Artificial intelligence and Internet of Things technologies such as model predictive control, deep reinforcement learning, adaptive comfort models, and integrated indoor air quality management have been reported to deliver measurable energy savings while sustaining or enhancing occupant comfort. The best performance is achieved when active AIoT-enabled systems are combined with passive measures appropriate for the climate. Persistent challenges include gaps in interoperability between systems, data governance issues, and the scalability of solutions in retrofitted buildings. The implications for professional practice highlight the need for interoperable, cyber-secure platforms aligned with retrofit standards such as the Publicly Available Specification 2035. Future research priorities include large-scale longitudinal validation, integration with renewable energy generation and district energy systems, refinement of personalised comfort control algorithms, and the development of user engagement strategies. By mapping the current evidence base and associated challenges, this review provides a reliable foundation for accelerating the adoption of artificial intelligence and Internet of Things technologies in smart buildings, supporting the pursuit of net-zero carbon emissions while enhancing occupant wellbeing.

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