Pressure Drops and Energy Consumption Model of Low-Scale Closed Circuit Cooling Towers

Heat transfer models of closed-circuit cooling towers are available in the literature. Using these models, traditional parametric studies show how the inlet conditions of the streams influence the cooling capacity. This type of analysis could yield to suboptimal operation of the cooling tower since optimal heat and mass transfer processes do not necessarily imply an energy efficient cooling device. The optimal design of closed-circuit cooling towers should include any evaluation of pressure loses associated with the three streams involved. Air-water biphasic pressure drop across tube bundles in such devices was not sufficiently investigated in literature. The proposed literature correlations depend on geometry parameters, and these parameters are not known. In this work, an experimental device has been designed and constructed to study pressure drops, and an energy consumption model has been developed. The pressure drop was successfully calculated modifying a general correlation proposed for two phase flow across tube bundles. The energy model results show that the optimum was obtained where the intube water Reynolds number is near the transition region, and at air velocities near 1 m/s

Centralized multivariable control by simplified decoupling

This paper presents a generalized formulation of simplified decoupling to n×n processes that allows for different configurations depending on the decoupler elements set to unity. To apply this decoupling method, the realizability conditions are stated. Then, from the previous decoupling in combination with a decentralized control, the formulation of a centralized control by simplified decoupling is developed. After reducing the controller, this last proposed method is modified to a multivariable PID control. From an implementation point of view, the windup problem is addressed for these methods, and an anti-windup scheme for multivariable PID controllers is proposed. Comparisons with other works demonstrate the effectiveness of these methodologies, through the use of several simulation examples and an experimental lab process

Object oriented modelling and simulation of hydropower plants with run-of-river scheme: A new simulation tool

This paper presents the design of a component library for modelling hydropower plants, and describes the development of a new simulation tool for small hydropower plants with a run-of-river scheme. After reviewing the desirable features of simulation, an approach based on an object oriented modelling language, like EcosimPro, is presented. A general model of hydropower plant with run-of-river scheme is created with this component library. It provides the possibility of choosing a specific number of turbines and spillway gates. In this way, several hydropower stations of similar operating characteristics can be simulated using this same general model. It is expected to obtain interesting information in simulation like the reservoir level, water flows, turbine efficiencies, and so on. In addition, a graphical user interface has been designed in order to operate this general model more easily, to configure plant parameters and to simulate the plant behaviour under different conditions. Three real stations have been used as real examples for validating the model and testing the simulator: hydropower stations of Villafranca and El Carpio (Córdoba, Spain) and Marmolejo (Jaén, Spain)

An extended approach of inverted decoupling

This paper presents an extension of the inverted decoupling approach that allows for more flexibility in choosing the transfer functions of the decoupled apparent process. In addition, the expressions of the inverted decoupling are presented for general n × n processes, highlighting that the complexity of the decoupler elements is independent of the system size. The realizability conditions are stated in order to select a proper configuration, and the different possible cases for each configuration are shown. Comparisons with other works demonstrate the effectiveness of this methodology, through the use of several simulation examples and an experimental lab process

Multivariable PID control by decoupling

This paper presents a new methodology to design multivariable PID controllers based on decoupling control. The method is presented for general n×n processes. In the design procedure, an ideal decoupling control with integral action is designed to minimize interactions. It depends on the desired open loop processes that are specified according to realizability conditions and desired closed loop performance specifications. These realizability conditions are stated and three common cases to define the open loop processes are studied and proposed. Then, controller elements are approximated to PID structure. From a practical point of view, the windup problem is also considered and a new anti-windup scheme for multivariable PID controller is proposed. Comparisons with other works demonstrate the effectiveness of the methodology through the use of several simulation examples and an experimental lab process

Inverted decoupling internal model control for square stable multivariable time delay systems

Accepted manuscriptThis paper presents a new tuning methodology of the main controller of an internal model control structure for n×n stable multivariable processes with multiple time delays based on the centralized inverted decoupling structure. Independently of the system size, very simple general expressions for the controller elements are obtained. The realizability conditions are provided and the specification of the closed-loop requirements is explained. A diagonal filter is added to the proposed control structure in order to improve the disturbance rejection without modifying the nominal set-point response. The effectiveness of the method is illustrated through different simulation examples in comparison with other works

Practical advantages of inverted decoupling

This paper presents a study of the main advantages of inverted decoupling in 2x2 processes. Two simulation examples and an experimental process are used to show these advantages in comparison with simplified decoupling. The study is focused on the following practical advantages: the apparent process is the same as that obtained if one loop changes to manual, bumpless transfer and anti-windup are achieved easily using a feedforward input in the controllers, and abnormalities of secondary loops do not affect the opposite loop. Thanks to them, inverted decoupling may be a good and easy way to improve the performance of industrial TITO processes with interaction problems (when it can be applied)

Educational tool for the learning of thermal comfort control based on PMV-PPD indices

In this paper, an interactive educational tool designed for the learning of thermal comfort concepts is presented. Thermal comfort is one of the fundamental aspects of indoor environmental quality and energy savings in buildings. Comfort-based control and energy management constitute an important emergent sub-discipline of engineering studies. The developed tool allows for the definition of the thermal model of a house. Based on this model, thermal comfort is estimated through the predicted mean vote (PMV) and predicted percentage dissatisfied (PPD) indices, and energy consumption is also calculated. The tool can communicate through Modbus TCP/IP protocol, providing external connectivity and data collection from the different sensors available in a building management system (BMS). In this way, it is possible to calculate in real-time the aforementioned comfort indices and propose corrective control indications to maintain the indoor-air conditions inside the optimal comfort range. A simple control strategy that can be applied to conventional HVAC systems is also addressed. The tool is available for degree students in control engineering. A survey was performed to evaluate the effectiveness of the proposed tool