This paper assesses the simultaneous influence of compressor speed and expansion valve opening on the thermodynamic performance of a plug-in (cassette) refrigeration system, running under different control strategies. Two different system configurations were investigated: (ⅰ) variable speed compressor (VSC) and capillary tube (CT); and (ⅱ) VSC and electric expansion valve (EEV). A dual SISO (Single-Input, Single-Output) control strategy was devised based on two PI controllers, one for the compressor speed and another for the expansion valve opening. The former senses the return air temperature, while the latter senses the superheating degree at the evaporator exit. It was found that the average energy consumption of the VSC/EEV when compared to the VSC/CT configuration decreased by as much as 10.1%, depending on the cassette operation regime and ambient temperature.
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