## 6 Conclusions  
The analysis and design of a control system that optimizes the time of use in a solar-assisted air-conditioning system were accomplished in this work. The main objective is to optimize the refrigeration cycle by an ejector for a solar air-conditioning system, using a single controller, optimizing physical resources and minimizing operating and maintenance costs. The priority is to increase the time of use of a solar air-conditioning system, thus facilitating its implementation, maintenance and easy development. A control structure based on two layers was designed. The first layer implements a temperature-control system of a storage tank, which follows a reference defined by a supervisory control layer. The second layer is supervisory control and optimization, which automatically generates a series of references for better performance of the air-conditioning. These references take into account solar-power supply conditions, user-defined modes of operation and disturbances of the system, thus optimizing the cost function based on the longest possible time of use. The advantage of this concept is being able to perform the optimization easily for a set of operation modes in the same refrigeration cycle controlled by the same controller, in spite of unknown dynamics and perturbations. Three simulations with different modes of operation are analyzed; the first mode of operation, called Mode 0, is the most economical; the second mode of operation, called Mode 5, is the least economical, but has higher cooling power; and lastly, variable mode is performed, in which cooling capacity depends on the selection of functioning modes by the end users. The simulations show that a fuzzy governor control can be optimized to obtain better performance in terms of time of use of a solar thermal system for residential applications. The operating tests prove that a time of use of approximately 17.55 h can be obtained in an optimized mode of operation in power economy. However, without an optimized control system and at the same conditions of  
Figure 23: Comparison of the generator temperature of the three modes of operation with a solar radiation of 500 kW/m\({}^{2}\). Figure 22: Mass flow for Modes 0 and 5.  
functionality, solar air-conditioning would only work approximately for 14.85 h, in the case of a single point of operation, for which it was designed. Fuzzy intelligent controls and optimization systems were compared for a typical operating day, with real and simulated solar radiation, showing that it is possible to improve the performance and reliability of nonlinear solar thermal systems in several ways:  
* Greater scalability, facilitating different operation points in an ejector-based refrigeration cycle, without the need for reconfiguring the system. * Increased usage time of a solar air-conditioning system, thus facilitating their implementation, maintenance and easy development. * Different tests show that the intelligent optimization and control systems are self-adapting to the end user requirements, disturbances and climatic conditions. * Less human supervision required. * No need to use electrical installations for the operation and use of solar air-conditioning. * Lower cost of implementation, maintenance and nonrenewable energy consumption. Finally, the tests performed demonstrate that the designed control structure optimizes the time of use before different conditions, the selection of functioning modes by end users, disturbances and solar radiation. This work has been supported by University of Colima (Mexico), Agrobiotechnology Laboratory of University of Colima (Area: Automation, Instrumentation, and Control) and the National Council for Science and Technology (CONACYT) of the Mexican Republic, with support for the high-quality graduate program, Announcement 15\(3\)2015\(1\)1 and Reference 005016. [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] jointly contributed to the design of the control strategy, simulations, data analysis and writing of the paper.