Um estudo experimental sobre a viabilidade técnica da utilização de inversores de frequência monofásicos em resfriadores de leite de pequeno porte visando o aumento da eficiência energética

Abstract

In Brazil is estimated that there are about 1.3 million dairy farmers, with an estimated 86 % of these producers being considered as small and medium producer. These producers face various problems, some of which are related to milk cooling tanks, such as little or no flexibility in temperature control of the stored milk or low-quality control devices, resulting in a high energy consumption and/or reduced quality of stored milk. For these reasons, the aim of this thesis is the study of economic viability of the use of frequency inverters in milk cooling tanks used by small milk producers in order to improve the consumption of electric energy. As innovation, this work is dedicated to introducing a compressors speed control on equipment available in the market, allowing the producers to reduce the energy expenditure with few changes in existing equipment. For this, several experiments were performed using a cooling tank, with a limit capacity of 0.35 m³, with two volumes of liquid (0.1 m³ and 0.3 m³). Tests were carried out by applying three types of temperature control, two of them being ON-OFF and the other using a PID (Proportional-Integrative-Derivative) controller. Performance tests show that the proposed control resulted in an increase of thermal and energy efficiency when operating at low frequencies compared to the manufacturer's 60Hz ON-OFF standard. The main conclusion was that the lower the operating frequency, the lower the volume of liquid in the reservoir, and the smaller the thermal hysteresis, the greater the energy efficiency of the system.