## 1 Introduction
Efforts to minimise energy usage with passive design approaches such as natural ventilation and sun orientation have been reported, but they sometimes come at the expense of consistent comfort [18; 19]. Emerging technologies, such as earth-air heat exchangers and phase-change materials, promise to overcome this gap by enabling temperature control without depending on energy-intensive mechanical devices [24]. Personalised thermal comfort systems, which employ wearable technology and IoT to adjust indoor settings to an individual's preferences [25], have the potential to increase comfort while lowering total energy con  
Figure 2: Internet of things (IoT) technologies [20]. sumption [26], since they permit more variable indoor circumstances. Moreover, machine learning methods are being investigated to forecast and adjust for occupant temperature preferences in real-time, boosting the flexibility of green building systems [27]. Despite these developments, the industry lacks comprehensive models incorporating different tactics, such as passive design, sophisticated materials, and customised systems, into a unified framework for enhancing thermal comfort in green buildings [28]. In addition, the scalability and applicability of these technologies to various climatic conditions and building types remain subjects for further study. In the dynamic realm of green building HVAC systems, the novelty of this manuscript stands out amidst a plethora of academic contributions. While several papers have traversed the technical intricacies of HVAC systems or delved into the singular facets of green buildings, this review offers an unparalleled, holistic perspective. It amalgamates discussions spanning occupant comfort, technological innovations, and market dynamics and ventures into the often-overlooked physiological and psychological dimensions governing thermal comfort. Another distinctive feature is the manuscript's exhaustive exploration of emergent HVAC technologies, such as Variable Refrigerant Flow (VRF) and phase-change materials, providing a rich, comparative analysis that might surpass many contemporaneous reviews [12]. However, this manuscript truly carves its niche in its candid exposition of the challenges plaguing the integration of traditional HVAC systems into green edifices. This, coupled with actionable insights and potential remedial measures, addresses a lacuna that remains conspicuously absent in many other works. Furthermore, introducing the adaptive comfort model, a paradigm that hinges on an occupant's experiential adaptability, infuses a fresh, human-centric perspective, balancing the often technocentric narratives of other reviews. With its judicious blend of technical depth, human considerations, and real-world implications, this manuscript distinguishes itself as a seminal contribution, poised to reshape the discourse on HVAC systems in green buildings [8]. The groundbreaking aspect of this study lies in its comprehensive approach to addressing the integration of traditional HVAC systems within the framework of green building principles. While previous research may have separately touched upon energy efficiency, occupant comfort, or the environmental impact of HVAC systems, this study is novel in its holistic examination of all these elements in tandem. Moreover, its emphasis on the economic implications of integrating traditional HVAC systems into sustainable designs provides a fresh perspective that goes beyond the environmental discourse [13]. Another pioneering feature is its exploration of eco-friendly refrigerants, a topic that, until now, has been underrepresented in mainstream research. This study also stands out for its in-depth look at retrofitting challenges, offering a unique blend of theoretical insights and practical solutions [21]. By bridging the often-separate worlds of sustainable construction and HVAC system design, this research introduces a groundbreaking narrative set to shape both industries and inspire further interdisciplinary research.