Devising a method to improve the accuracy of maintaining the preset temperature and humidity conditions at a vegetable storage facility under a food storing mode

Abstract

A vegetable storage facility is an energy-consuming object with distributed parameters. The quality of product storage depends on the microclimate in the vegetable storage facility: current temperature, humidity, and carbon dioxide level. Existing temperature controllers in a veg etable storage facility use a two-position law of control, which leads to the consumption of excess energy and product spoilage. The purpose of the study is to improve the work of the controller in the process of product storage at the storage phase due to closing the two-position controller through feedback in the form of a first-order aperiodic link. To achieve the goal, the procedure for calculating the transfer function of a control object through the equation of thermal balance was used. This procedure made it possible to take into consideration the parameters of a vegetable storage facility: the area and the type of thermal insulation material of floorings, the weight, and the type of a stored product, as well as thermal energy supplied to the vegetable storage facility.Based on the heat balance equation, the nature of the operation of controlling elements, transfer functions of a vegetable storage facility without a product, and the vegetable storage facility filled with a product, were calculated. The heat model of a vegetable storage facility was constructed in the MATLAB Simulink environment (USA) to check the algorithms of the temperature field control. The product storage for 180 days with changes in the daily temperature of outdoor air from minus 8 °C to plus 2 °C and changes in humidity from 50 % to 100 % was modeled. According to the results of modeling, it is possible to conclude that the addition of an aperiodic link to the feedback of the two-position controller will enable taking into consideration the inertia of a control object. This allows decreasing the maximum error in control of self-oscillations to 0.15 °C and decreasing the total operation time of con trolling elements by 13 %