I am learning about HVAC, can someone explain to me what is a saturation temperature?
Is it the temperature inside of the house or walk in cooler?

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Refrigeration Technologies: Manufacturer of food grade NSFapproved products (http://www.refrig.com/charge.html)

Simple answer is that it is the point at which a liquid is evaporating and condensing at the same rate. In terms of room comfort it would be 100% humidity. In refrigeration? Similar, just that the "room" is the inside of a cylinder or the system. :-)