## 4 Eco-Friendly Air-Conditioning  
Recent advances in eco-friendly design and materials for outdoor air conditioning systems have been made to meet rising concerns about energy usage and environmental effects. This event marks a turning point in the industry's transformation to more eco-friendly and sustainable practices [37]. 1. Using sustainable refrigerants is one of the most critical aspects of eco-friendly design. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), both potent greenhouse gases, were widely used in conventional air conditioning systems. However, more contemporary outdoor cooling systems favour using hydrofluoroolefins (HFOs) and natural refrigerants such as ammonia and carbon dioxide [38]. These alternatives are less environmentally harmful and less likely to contribute to global warming. 2. Heat recovery technology: Incorporating heat recovery technology is another breakthrough. Outdoor cooling systems may collect and reuse waste heat generated during the cooling process [39]. This reduces total energy use while enhancing energy efficiency. Systems for heat recovery are particularly beneficial in commercial and industrial settings that generate a great deal of heat, which may be utilised for activities such as water heating [37]. 3. Energy-efficient components: Eco-friendly design involves using energy-efficient materials and components. High-efficiency compressors, fans, and heat exchangers are merely a few examples of the elements utilised in outdoor air conditioning systems that have reduced energy consumption [40]. These components help reduce energy use, which benefits the environment and saves users money. 4. Sustainable production methods: The production of outdoor air conditioning systems goes beyond the working stage. Manufacturers progressively embrace eco-friendly manufacturing practices [41] to decrease waste, use less energy and water during production, and construct cooling units out of recycled or recyclable materials. These measures reduce the carbon footprint of the manufacturing process. * Regulatory conformity: Government regulations and industry standards have considerably impacted adopting eco-friendly design and materials in outdoor air conditioning technologies. The Montreal Protocol and its revisions have pushed the industry toward more sustainable practices by emphasising the elimination of ozone-depleting chemicals and decreasing refrigerants with a high GWP (global warming potential) [42]. The transition to environmentally friendly outdoor air conditioning systems is a multifaceted industry shift fuelled by technological innovation, sustainable manufacturing, and regulatory compliance. Green refrigerants, such as hydrofluoroolefins (HFOs) and natural chemicals, such as ammonia and carbon dioxide, have a lower global warming potential (GWP) than conventional hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) [43]. This development is partly the outcome of international legislation, such as the Montreal Protocol, which seeks to eradicate ozone-depleting substances. Particularly helpful in commercial and industrial settings is the implementation of heat recovery technology, which recovers waste heat produced during the cooling process to reduce overall energy consumption and boost system efficiency [35]. The emphasis on environmentally responsible design also extends to using energy-efficient components, such as high-efficiency compressors, fans, and heat exchangers, which minimise energy consumption and cut operating expenses. Beyond the operational phase, manufacturers are adopting sustainable practises in producing these systems, such as reducing waste, minimising energy and water consumption, and utilising recycled or recyclable materials, per the principles of circular economy and sustainable development [44]. Regulatory frameworks such as the Montreal Protocol have played a significant role in pushing these changes by providing the economic and legal incentives necessary for the sector to adopt more sustainable methods.