An indirect refrigeration system is defined as:

An indirect refrigeration system is characterized by having the evaporator located away from the space that needs to be cooled. This means that rather than directly cooling the air or fluid in the space to be refrigerated, the system first cools another secondary fluid, which is then circulated to transfer the cooling effect to the desired area. This setup allows for better control of temperatures and can be more efficient in certain applications, especially in larger systems where direct cooling would be impractical.

The other options describe characteristics that do not accurately define an indirect refrigeration system. For example, an open evaporator suggests a direct method of cooling, implying that the refrigerant interacts directly with the air or fluid in the space. Direct compression refers to systems where the refrigerant goes through direct compression cycles, which is not a feature unique to indirect systems. Lastly, not all indirect setups require a cooling tower; cooling towers are typically associated with specific types of chilled water systems and are not a requirement across all indirect refrigeration scenarios. This context underscores why the definition of an indirect refrigeration system centers on the positioning of the evaporator.