Linear compressors for refrigeration: benefits and challenges

Linear compressors have significant advantages over conventional crank-driven compressors, notably their high motor efficiency, resonant operation, small size and simple capacity modulation. A number of linear compressors have been incorporated into vapour compression refrigeration (VCR) units in domestic refrigeration systems, including fridge/freezers and air conditioners. Oil-free operation allows the use of micro-channel heat exchangers for miniature refrigeration systems for electronics cooling. The moving magnet type linear motor has become a major trend due to its high efficiency and compactness. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency in order to reduce the input current required. Designing compact suspension systems for higher resonant frequency is very challenging.

However, the main challenge is cost. For electronics cooling, a miniature linear compressor means that the miniature VCR system is not cost effective compared with other solutions. For household refrigeration, the major cost of manufacturing linear compressors comes from the material. Motor design using permanent magnets (e.g. NdFeB) can be cost effective. Contacting seal designs can be considered, as they seem to be an attractive option that could simplify manufacture and reduce material requirements (coating etc.) and therefore cost. In order to manufacture linear compressors on a large scale, a minimum of sensors and actuators are required. Inductive sensors can be used for detecting the piston position. With further R&D, more cost effective linear compressor products will hopefully appear in the near future.

Source: LIANG K. A review of linear compressors for refrigeration. International Journal of Refrigeration [online]. 2017, vol 84, p. 253-273. Available in Fridoc