Abstract
This paper describes the complete integration of a fuzzy control of multiple evaporator systems with the IEEE 802.15.4 standard, in which we study several important aspects for this kind of system, like a detailed analysis of the end-to-end real-time flows over wireless sensor and actuator networks (WSAN), a real-time kernel with an earliest deadline first (EDF) scheduler, periodic and aperiodic tasking models for the nodes, lightweight and flexible compensation-based control algorithms for WSAN that exhibit packet dropouts, an event-triggered sampling scheme and design methodologies. We address the control problem of the multi-evaporators with the presence of uncertainties, which was tackled through a wireless fuzzy control approach, showing the advantages of this concept where it can easily perform the optimization for a set of multiple evaporators controlled by the same smart controller, which should have an intelligent and flexible architecture based on multi-agent systems (MAS) that allows one to add or remove new evaporators online, without the need for reconfiguring, while maintaining temporal and functional restrictions in the system. We show clearly how we can get a greater scalability, the self-configuration of the network and the least overhead with a non-beacon or unslotted mode of the IEEE 802.15.4 protocol, as well as wireless communications and distributed architectures, which could be extremely helpful in the development process of networked control systems in large spatially-distributed plants, which involve many sensors and actuators. For this purpose, a fuzzy scheme is used to control a set of parallel evaporator air-conditioning systems, with temperature and relative humidity control as a multi-input and multi-output closed loop system; in addition, a general architecture is presented, which implements multiple control loops closed over a communication network, integrating the analysis and validation method for multi-loop control networks designed for multi-evaporator systems.
Highlights
A multi-evaporator system is an air-conditioning system configuration where there is one outdoor condensing unit and multiple indoor units, in which the system has the ability to control the amount of refrigerant flowing to the multiple indoor units, enabling the use of many evaporators of differing capacities and configurations connected to a single condensing unit
Each repeater node (R) implements at least two aperiodic tasks to transmit the values to other nodes; in most cases, they allow it to be part of multiple paths between the smart sensor to the controller in the smart agent and the controller to the smart actuator, and in this case, they must implement at least two tasks for each route that is involved, which are scheduled by the earliest deadline first (EDF) algorithm and, a minimum real-time kernel that executes real-time tasks running under the EDF scheduler, which must be running on the nodes
We are interested in the performance analysis of wireless sensor and actuator networks (WSAN) for the development of real-time control applications in non-beacon mode, as is the case of multi-evaporator systems; this mode has a greater scalability, self-configuration of the network and the least overhead, but it must be implemented in processes that require slow dynamics and, thereby, ensuring minimal real-time features
Summary
A multi-evaporator system is an air-conditioning system configuration where there is one outdoor condensing unit and multiple indoor units, in which the system has the ability to control the amount of refrigerant flowing to the multiple indoor units, enabling the use of many evaporators of differing capacities and configurations connected to a single condensing unit. The work in [8] proposes as a solution for ventilation problems in variable refrigerant flow (VRF) systems, a VRF unit and outdoor air (OA) processing unit combined air conditioning system, using the same simulation scenario of six floors divided into 25 air-conditioned zones; they use the ready-made multi-zone building model provided by TRNSYS, and the results obtained by them show that all of the zones of the combined system proposed could maintain their specific set-points within a small error after the control is stabilized, regardless of the set-points being the same or different For this purpose, a fuzzy control system [9,10] is used here to control a set of evaporators. Validation, results and discussions of the simulation are carried out in Section 6, and Section 7 concludes this study
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