Projeto de um controlador para o ajuste da temperatura de saída da água de uma bomba de calor a CO2 com evaporador solar

Abstract

The growing global concern about the environmental impact caused by contemporary society leads to an increased interest in the use of renewable and more efficient energy sources. In this context, there is great interest in the use of heat pumps for domestic water heating. This work presents a control algorithm for the water outlet temperature of a heat pump with a direct expansion solar evaporator for residential water heating, that uses CO2 as its refrigerant. During the development of this study, several experimental tests were made with a prototype of a heat pump for domestic use, in order to evaluate the dynamic system response to step-like perturbations in the water flow. With the data obtained in this process, it was possible to identify the system dynamic model. After that, a PID (Proportional-Integral-Derivative) controller was developed and tuned using methods described in the literature. The developed controller was evaluated through computational simulations in order to determine its robustness, disturb rejection, stabilization time and error in a steady state. Thanks to the usage of quantitative validation methods, it was possible to develop a transfer function that has a similarity percentage greater than 80% when compared to the experimental data. Using different performance rates, among the studied methods, the best tuning method for the heat pump controller system was determined as being the ITAE- servo method. The controller tuned by this method turned out to be the best as to control the outlet temperature of the water, with a steady state error of 5.2x10-6°C and a stabilization time of 225s.