The fundamental principles of refrigeration systems include the laws of thermodynamics, heat transfer, and fluid flow. The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. The second law of thermodynamics states that the total entropy of an isolated system always increases over time. In refrigeration systems, heat is transferred from a lower temperature to a higher temperature, defying the natural direction of heat flow, through the use of refrigerants and mechanical work. Understanding these principles is crucial for designing and operating efficient refrigeration systems.