Research on solar adsorption refrigerators began in China in the 1990s, but most remained confined to the laboratory and had yet to achieve the desired level of practical application. This was primarily due to the high production temperatures and the limited availability of solar energy. Furthermore, the need for piping between the outdoor adsorption bed and the indoor cooler in solar adsorption refrigerators was a major obstacle to their mass production.
To address these limitations, domestic researchers conducted a detailed analysis of solar solid adsorption refrigeration technology, focusing on various aspects, including system cycle mechanisms, the selection of adsorption refrigerant pairs, solar refrigerator performance, internal and external characteristics analysis, and optimized design. After years of dedicated research, Sun Changjiang from the Thermal Environment Laboratory at the Institute of Refrigeration at Shanghai Jiao Tong University built two solar adsorption refrigerators using the processes and procedures required for mass production. The experimental results demonstrated relatively stable performance, demonstrating that the technology for this type of solar refrigerator is mature enough for production.
In solar adsorption refrigerators, the selection of adsorption refrigerant pairs is crucial. Domestic researchers have attempted to study the adsorption properties of various adsorption pairs, including CoF2-NH3, SrCl2-NH3, activated carbon-methanol, and activated carbon-ethanol. Experimental results show that the CoF2-NH3 pair has a high specific adsorption capacity, requires a low temperature for maximum adsorption, has a short adsorption cycle, and exhibits no agglomeration or expansion after repeated adsorption, offering new possibilities for the miniaturization and practical application of chemical adsorption refrigeration systems. The SrCl2-NH3 pair has a high adsorption cooling capacity and is suitable for use with solar energy or low-grade waste heat, making it an excellent pair. The activated carbon-methanol pair is more suitable for use in solar solid adsorption ice makers than the activated carbon-ethanol pair.
High-efficiency solar thermal collectors are key components of solar refrigerators and are classified into two types: non-focusing and focusing. Non-focusing solar collectors are categorized as flat-plate, vacuum tube, and CPC. These three types have low collection temperatures, below 250°C, and are classified as low- or medium-temperature solar collectors. Focusing solar collectors are categorized as trough, dish, and tower types. Typically, these three types can achieve collection temperatures exceeding 300°C, making them medium- and high-temperature collectors. For solar refrigerators, non-focusing solar collectors are primarily used in solar adsorption refrigeration systems, while focusing solar collectors can be used in solar photovoltaic refrigeration systems. Research and utilization of solar collectors, both domestically and internationally, has primarily been limited to the medium- and low-temperature range.