Smart Control for Smarter Buildings: A Review of Traditional and Intelligent HVAC Control Strategies Toward Energy Sustainability

Heating, Ventilation, and Air Conditioning (HVAC) systems are among the largest energy consumers in buildings, and their control strategies play a crucial role in achieving energy efficiency, indoor comfort, and sustainability. This review examines the main HVAC control strategies, ranging from traditional methods to Internet of Things (IoT) based and Artificial Intelligence (AI) driven approaches. In addition, occupancy-based control strategies and energy-efficient designs are critically examined for their potential to enhance system responsiveness and reduce operational costs. More than 100 recent research studies were systematically analyzed and compared across key parameters such as the objective of the study, the used control technique, strength, weakness, opportunity, threat, software/tool used, building type (residential, commercial, or industrial), control scale (single zone/multi-zone), and specific HVAC part controlled (e.g., AHU, VAV). To enable consistent comparison, a Multi-Objective Robustness Criterion (MORC) is used to assess how different control strategies balance energy consumption, thermal comfort, and Indoor Air Quality (IAQ) under changing conditions and how each control technique overcomes the limitations of the previous ones. In addition, the review also introduces a case analysis based on three U.S. cities, Charlotte, Greensboro, and Raleigh, to demonstrate the impact of outdoor climate variations and occupancy pattern on HVAC energy consumption. The results show that even a one-degree change in outdoor temperature can cause a considerable increase in annual energy consumption. Moreover, occupancy-based HVAC control can save more than $7,000 annually in the studied educational building. These findings highlight the strong impact of location-specific temperature differences on HVAC performance and emphasize the need for adaptive, climate-aware control strategies, while also pointing to future directions for smarter and more energy-efficient HVAC systems.