The world is currently dealing with the issue of ever-increasing pollution and climate change. There is a need for sustainable actions in all sectors, especially in the automobile industry. Pollution levels are skyrocketing as the automobile industry expands daily. IEA, 2019, the global CO2 was about 43.2 giga ton (Gt) per year, and was about 20% higher than 2013 (Friedlingstein et al., 2014; Shahzad et al., 2017). According to (IEA, 2020) statistics, worldwide transportation emissions climbed by less than 0.5% IEA, 2019 compared to 1.9% yearly since 2000, mainly to improvements in efficiency, increased electrification, and higher use of biofuels. Despite this, transportation still accounts for 24% of direct CO2 emissions from fuel burning. The emissions due to cars, buses, trucks, and 2 & 3 wheelers account for about three-quarters of all CO2 emissions from transportation, while emissions from aviation and shipping continue to rise. Fig. 1 shows the CO2 emissions due to transport sector considering the Sustainable Development Scenario, 2000–2030.
It is predicted that nearly one billion vehicles are driven on the road worldwide, with that figure expected to double by 2035 (Bentrcia et al., 2017; McEvoy, 2015) and they consume a significant amount of fuel per year. The automobile and transportation sector accounts for about 30% of all energy consumption worldwide (Omi, 2009), and about 90% of this energy originates from fossil fuels (Bentrcia et al., 2017). According to the reports by (IEA, 2019), Mobile air conditioning (MAC) currently consumes about 1.5% of current global oil consumption, or more than 1.8 million barrels of oil equivalent per day (Mboe/d). According to the literature, MAC consumes approximately 6% of the annual global energy consumed by cars. Depending on the climate, driving habits, and traffic congestion, this energy consumption ranges from 3% to 20%. In hot climates and congested traffic, this energy consumption can reach a maximum of 40%. As per (IEA, 2009) statistics, the global energy consumption for transport had increased steadily about 2%–2.5% annually and Fig. 2 shows the energy consumption of different modes of transportation from 1971 to 2006.
The increase in automobiles used for commuting has created a new problem: the necessity for air conditioning (AC) in vehicles to ensure human comfort. Climate change and population growth are strongly tied to the requirement for AC. Fig. 3 depicts the environmental conditions that influence an automobile's interior temperature. The performance of an automobile's HVAC system is influenced by absorbed heat. Fig. 4 depicts the several elements that influence the quantity of heat absorbed inside the cabin.
The use of AC systems has increased energy consumption in automobiles, resulting in climate change and adverse environmental effects. The United States alone consumes about 7.1 billion gallons of gasoline each year for automobile AC systems (Johnson, 2002). This high increase in energy consumption has made AC systems the second-largest fossil energy user after automobile propulsion. The energy required to operate an automobile AC system is significantly greater than the energy required for an engine to drive a mid-sized vehicle at a steady speed of 56 km/h, and fuel economy can decrease by nearly 0.4 km/L if a conventional engine is subjected to a 400W load (Farrington and Rugh, 2000). In few studies, it had been reported that in conventional Internal combustion engine (ICE) vehicles, HVAC systems increases fuel consumption by up to 30% (Bentrcia et al., 2018; Onoda and Gueret, 2007; Subiantoro et al., 2014). The automobile is driven for about 249 h annually (Sand and Fischer, 1997) or about 4.8 h per week. The usage of automobile AC system accounts for about 107–121 h annually, which is 43–49% of vehicles energy consumption (Fischer, 1995). The refrigeration system used in transportation trucks also have high fuel consumption and utilises about 40% of the total fuel required to run a vehicle (AlQdah et al., 2010; Pandya et al., 2020). Even for electric vehicles (EVs), the HVAC system can reduce the driving range by about 30–40% (Farrington and Rugh, 2000; Lee et al., 2013; Z. Zhang et al., 2018a). The HVAC system for the hydrogen driven fuel cell electric vehicles (FCEV) also increases energy consumption, i.e. nearly 3%–12.1% surge in hydrogen consumption (Pino et al., 2015).
With the unparalleled growth of automobile air conditioning (AAC), it was assumed that this would reach an industry-wide penetration rate of 70% by 1980 and was of great concern to the automobile industry. The automobile industry shifted from R12 to R134a when the Montreal Protocol was established in 1989 to protect the ozone layer as R12 has a high Ozone Depleting Potential (ODP), but R134a has zero. The most used refrigerant in AAC system is R134a. After the Kyoto protocol in 1997, the main aim was to control the use of R134a refrigerant due to its high value of Global Warming Potential (GWP). The United Nations has banned the use of current refrigerants that have a GWP value of more than 150. The Kyoto protocol was made to improve the current (R134a) refrigerant system by preventing leakage. However, seeing the high GWP value, i.e., 1430 of R134a, there is a need for new and alternative refrigerant to replace R134a (Vaghela, 2017; Yoo and Lee, 2009). Fig. 5 shows the development of refrigerants with the change in cooling methods.
The AC system is an integral part of the vehicle, consumes a considerable amount of energy, this leads to higher consumption of fuels, leading to the rise in harmful emission and pollution levels. Therefore, the automobile industry must find new sustainable AAC system and eventually shift towards the use of electric vehicles (EVs). The EVs are an environmental solution, but the HVAC system in EVs also consumes a good amount of energy, resulting in a reduction in the driving range of the vehicles. In the last 4–5 years, various research was done to optimize energy management of HVAC system in EVs and the interrelation with the driving range of EV (Aceves, 1996; Al Faruque and Vatanparvar, 2016; Pan et al., 2019; Song et al., 2015; L. Zhang et al., 2018b).
For the last few years, industries and researchers are working together to tackle the negative effect on the environment due to conventional AAC systems. As the fuel consumption to operate an AC system is inversely proportional to its COP. To reduce fuel consumption of an automobile, the COP of the AAC must be high. The recent research showing the COP trends of different AAC system is tabulated in Table 1. The main objective of the various studies is mainly focused on the energy management of HVAC systems in an automobile. The energy consumption is reduced by finding different solutions, enhancing, and developing different AAC system methods. Although a substantial amount of growth has been observed in the automobile and its HVAC systems. However, the current AAC systems have a few limitations, such as high GWP value refrigerant, the system energy consumption, size, weight, and the main problem is environmental pollution. Although EVs are an eco-friendly solution to conventional vehicles, however the HVAC system in EVs also consumes a good amount of energy, resulting in a reduction in the driving range. This review provides a broad insight into various HVAC systems used in conventional and electric vehicles to overcome all these limitations. This review provides a detailed investigation of different AAC systems and their coalition with the vehicle performance. The various methods of the AAC system are categorized into active, passive and hybrid AC systems. The comprehensive description of different AAC systems is reviewed, compared, and described in this article. Within the information and knowledge promulgated in this review article, the evolution of future sustainable AAC systems can be expedited. It could serve as a foundation for the development of a future optimised sustainable AAC system. The various AAC systems reviewed in this article are represented in Fig. 6.