State-of-the-art air-conditioning technologies

Air conditioning is the process of regulating air’s temperature, humidity, ventilation and circulation, as well as cleansing air, for an enclosed space to achieve the desired comfortable environment. Modern air conditioning has existed for more than a century and plays an essential role in not only providing thermal comfort for human occupants, but also maintaining suitable thermal conditions for heat-sensitive devices and systems. The most common air-conditioning technology is developed based on the vapor-compression refrigeration cycle, which is also known as the conventional air conditioning in contrast to many other competing technologies. Despite the conventional air conditioner being the most widely adopted cooling technology and its market size still growing, its energy consumption and greenhouse gas emissions remain challenging issues. Therefore, a lot of efforts are being made to develop novel alternative approaches that are environmentally friendly and energy-efficient. This chapter will review some recent state-of-the-art air-conditioning technologies with a specific focus on cooling as this is the most difficult part in air conditioning from the thermodynamic perspective. Having a deeper appreciation on the importance of developing energy-efficient cooling technologies and their impacts on the environment, evaporative cooling, being as the key technological subject of this book, will be gradually introduced.