Analysis and Control of a Vapour Compression System with Internal Heat Exchanger

This Thesis has been carried out in the downline of a curricular internship at VIS Engineering. VIS is a consulting company providing advanced technology services for energy systems focusing on vapor compression cycle (VCC) systems. The study centers on VCC systems utilized in Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC&R) applications, which serve as fundamental components supporting essential cooling and heating functions. These systems play a critical role in maintaining, e.g., comfortable indoor environments and preserving perishable goods across residential, commercial, and industrial sectors. Specifically, the study addresses the analysis and control design of a chiller system featuring an internal heat exchanger, utilizing an established MATLAB-based simulation environment. Initially, a Global Sensitivity Analysis (GSA) was conducted to understand the relative significance of various factors, such as system parameters, inputs, and disturbances, on the chiller output variables, thereby elucidating overall system performance characteristics. Then, a hierarchical control framework was devised, including a lower layer with three decentralized PID loops and an upper layer dedicated to real-time optimization (RTO) of the chiller energy efficiency. Within the RTO task, two Extremum Seeking Control (ESC) solutions were implemented: a perturbation-based ESC and a dither-free one. The simulation outcomes shed light on the challenges, opportunities, and constraints associated with these control methodologies, providing valuable insights into their efficacy and limitations.