Energy-efficiency control of two-stage two-load-demand refrigeration cycles
- Autores: José Enrique Alonso Alfaya
- Directores de la Tesis: Manuel Gil Ortega Linares (dir. tes.), Francisco Rodríguez Rubio (dir. tes.)
- Lectura: En la Universidad de Sevilla ( España ) en 2018
- Idioma: español
- Número de páginas: 186
- Tribunal Calificador de la Tesis: Fernando Morilla García (presid.), Luis Fernando Castaño Castaño (secret.), Manuel Berenguel Soria (voc.), Manuel Vargas Villanueva (voc.), João Manuel Lage de Miranda Lemos (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Automática, Electrónica y de Telecomunicación por la Universidad de Sevilla
- Materias:
- Enlaces
- Tesis en acceso abierto en: Idus
- Resumen
Refrigeration systems based on vapor compression are the most extended method for cooling and freezing generation. Nowadays, this process has been spread out over the world, and in many difference fields, such as supermarket, human acclimatization, or even cars and computers. These facts, connected to large energy consumptions and increasing of fossil source scarcity entails the necessity to study these cycles and to optimize control.
This Thesis addresses the study, control, optimization and experimentation of vapor compression refrigerant cycles with up to two compression stages and two load demands from an energy-efficiency point of view.
The one-compression-stage two-load-demand configuration is generally extended in any commercial domestic refrigerator. Talking about industrial, several food companies required the control of their products at specific different temperatures, where this configuration plays an important role. Two-compressor two-load-demand configuration is less habitual but its optimization allows to reduce compressor dimensions while the thermal demands can be satisfied. This leads to increase safe energy and improve management capacity of the refrigerant powers required.
An experimental plant used as testbed is available for control, optimization and identification. It is configurable using up to two evaporators and up to two compressor. Air-cooled or water-cooled condenser can be selected and two tanks within a thermal resistance that simulates the secondary load demand are available to work at cooling and freezing temperatures. Although modeling, optimization and control are oriented to this experimental plant, methodology can be extended to others, experimental or commercial plants. More details about it are exposed, in addition to some technical information.
Understand the system dynamics is essential to improve the energy efficiency. Static models of each element involved in the cycle have been selected considering the experimentalplant components but for the condenser, which has been dynamically modeled since its responses are one order of magnitude lower than the others. Furthermore, iterative procedures have been designed and successfully tested for both configuration. Talking of the secondary circuits, tank dynamics have also been modeled for both temperature level considering experimental design.
Regarding the system identification, compressor and expansion valve parameters have been identified by mean of least square method, while a novel identification methodology has been proposed for evaporator and condenser based on static relationships between heat-transfer coefficients. Global validation has been done for the one-compressor twoload-demand configuration. Finally, the secondary tanks are studied and identified.
Robust control has been designed for one-compressor one-load-demand configuration considering several operation points. Controllability analysis is carried out to know system constraints. Reference-tracking and disturbance-rejection comparisons between robust, PID and model predictive controllers are done, revealing that the robust control show better performance.
Optimal operation of refrigeration cycles are a key point for energy efficiency. Optimization search based on the Coefficient of Performance and iterative procedures for both vapor-compression-cycle configurations have been developed and studied for large cooling and freezing power ranges. The one-compression two-load demand shows a smooth optimal maps where COP presents a great performance while the main compressor keeps at the lower speed possible. The two-stage two-load-demand configuration exhibit complex maps that depend on the constraints satisfied at each pair of thermal power required.
