How is "free air" defined in refrigeration terms?

In refrigeration, "free air" is defined as air at atmospheric conditions, which encompasses both its pressure and temperature. This means it is the natural state of air found in the environment, typically at sea level pressure (approximately 14.7 psi at 68°F or 20°C). This definition is significant in refrigeration applications, as it provides a baseline for understanding how air behaves under various conditions when it is either compressing, expanding, or being conditioned (heated or cooled) within a system.

The context of this definition is essential because refrigeration systems often operate by manipulating the properties of air, among other agents. Recognizing "free air" as air at atmospheric conditions helps technicians understand the baseline from which other thermodynamic variables will change when certain processes or system operations are performed.

Air with high humidity, a specific temperature, or pressurized air, while relevant in some contexts, does not align with the definition of "free air." Each of those conditions modifies the standard atmospheric air and can significantly impact the performance and efficiency of refrigeration systems, but they do not represent the concept of “free air” in its pure, unmodified state.