Simulation and Validation of Vapor Compression System Faults and Start-up/Shut-down Transients

The statistics from the US Department of Energy show that about one-third of the total consumption of electricity in the households and industries is due to the Air Conditioning and Refrigeration (AC & R) systems. This wide usage has prompted many researchers to develop models for each of the components of the vapor compression systems. However, there has been very little information on developing simulation models that have been validated for the conditions of start-up/shutdown operations as well as vapor compression system faults. This thesis addresses these concerns and enhances the existing modeling library to capture the transients related to the above mentioned conditions.

In this thesis, the various faults occurring in a vapor compressor cycle (VCC) have been identified along with the parameters affecting them. The transients of the refrigerant have also been studied with respect to the start-up/shutdown of a vapor compression system. All the simulations related to the faults and start-up/shutdown have been performed using the vapor compression system models developed in MATLAB/Simulink environment and validated against the 3-ton air conditioning unit present in the Thermo-Fluids Control Laboratory at Texas A & M University.

The simulation and validation results presented in this thesis can be used to lay out certain rules of thumb to identify a particular fault depending on the unusual behavior of the system thus helping in creating certain fault diagnostic algorithms and emphasize the importance of the study of start-up/shutdown transient characteristics from the point of actual energy efficiency of the systems. Also, these results prove the capability and validity of the finite control volume models to describe VCC system faults and start-up/shutdown transients.