Development of a control algorithm for chest freezers with variable speed compressors

A chest freezer is an electrically powered device with thermal insulation that can keep food frozen. The target average temperature for this device is -18°C, and it should be able to operate within different ambient temperature ranges according to its climate class. When its door is opened to remove some frozen food, it should be able to regain the lost heat or freeze non-frozen food. Freezers declared as Tropical (T) climate class should operate smoothly between ambient temperatures of 16°C and 43°C. For a product declared as sub-tropical, the maximum operating temperature is 38°C. For a product declared as sub-normal, the lowest operating temperature is 10°C. A product can be declared in multiple climate classes. For example, a product declared as SN-T is stated to meet both sub-normal and tropical conditions. In this case, it is indicated that the product will operate smoothly in ambient temperatures of 10°C, 43°C, and any temperature in between. This thesis focuses on developing a sliding mode control algorithm that can simultaneously meet the needs for energy efficiency and performance when using a variable-speed compressor in household deep freezers. In this context, a mathematical model of a household deep freezer with a variable-speed compressor is obtained, and compressor frequency variation is examined on this model. The effect of the sliding mode control algorithm on cooling performance and energy efficiency is experimentally tested and compared with the test results of products using fixed-speed compressors. The test results showed an improvement of 12-24% in energy efficiency and 26-67% in freezing capacity compared to the model. Keywords: Chest freezer, Variable speed compressor, Control algorithm, Energy efficiency, Cooling system