A study on the modeling of the minimal stable superheat for a variable speed refrigeration system

• Based on bubble dynamics theory, a critical stable condition is defined.
• The oscillation of the control loop is studied using the critical stable condition.
• We build a model for refrigeration system that is able to predict the MSS line.
• Varying superheat settings on the basis of the MSS line can lead to a higher COP.

This work presents a model for variable-speed vapor compression system that is able to predict accurately the minimal stable superheat (MSS) line. Based on bubble dynamics theory, a critical stable condition is defined, which the critical operating parameters of the evaporator should satisfy. Together with the model of the refrigeration system, the MSSs depending on different operating conditions are predicted successfully. This model has been validated experimentally with steady state tests, presenting a prediction error lower than 5%. Finally, it is found that, in a wide capacity modulating range, varying superheat settings on the basis of the MSS line can lead to a higher COP.