Air-conditioning and refrigeration: Current status and future perspectives

Abstract

Air-conditioning and refrigeration systems are essential facilities of health care, transportation and food preservation, which make people able to live and work at the coldest and warmest climates in the planet. These technologies have been applied to a wide range of scenarios, including the distributed air-conditioning, food, medicine, health and sport for people’s daily life, and centralized air-conditioning, heat pump and cryogenics in commercial and industrial applications. In the near future, global warming, urbanization and pursuit of higher living standard will continue to push the demand of air-conditioning. Food preservation for the increasing global population and fresh food e-commerce require more cold storage. Space detection, low-temperature imaging and cryogenic medical treatment will push the cryogenics forward. Except for these listed applications, there are also many other driven forces for the next-step development of air-conditioning and refrigeration, which make its future progress complicated. A comprehensive summary of the current status is necessary for air-conditioning and refrigeration, which will also provide us the basis to analyze its future perspectives. Three typical air-conditioning and refrigeration technologies are introduced at first. These include the refrigeration/heat pump, temperature-humidity control and cryogenics. Vapor compression refrigeration, absorption refrigeration, adsorption refrigeration, ejector refrigeration, solid state refrigeration, refrigeration without thermodynamic cycles and heat pumps are introduced for the first topic, which focuses on the temperature manipulation in normal temperature range. Condensation dehumidification, solution dehumidification, solid desiccant dehumidification and evaporative cooling are introduced for the second topic, which focuses on the interaction of temperature and humidity of air. Gas liquefaction and cryocooler are introduced for the third topic, which focuses on the thermal energy removal under low temperature. Conventional and emerging applications of these technologies are introduced afterwards. The refrigeration and dehumidification could support a wide range of application including air-conditioning, data center cooling, solar cooling, electrical vehicle thermal management and food/drug preservation. The applications of heat pumps include the clean heating supply and industrial heat recovery. The cryogenics could be applied for air liquefaction, liquefied natural gas, hydrogen storage, cryobiology/cryomedicine and big science project. Based on the previous analysis, future challenges on efficiency enhancement, eco-friendly refrigeration and application promotion are presented at last. The efficiency enhancement is driven by the numerous equipments of air-conditioning and refrigeration in use, which consume a large portion of total power consumption of mankind. It could be achieved through the innovation on heat exchanger, thermodynamic cycle and intelligent control. The eco-friendly refrigeration is driven by the environmental protection policies. Low GWP and ODP refrigerants including HFOs and natural refrigerant will be effective solutions. Small-sized heat exchanger with less refrigerant charge is also important. The application promotion is driven by the fact that air-conditioning and refrigeration have already become the basic technology supporting the emerging technologies. Except for the traditional applications, the air-conditioning and refrigeration technologies are becoming fundamental technologies for many multidisciplinary fields, including the data center cooling, electrical vehicle thermal management, clean heating, industrial waste heat recovery, cryobiology/cryomedicine, and big science project.