The key thermodynamic properties of refrigerants that affect their performance in HVAC systems include their boiling point, latent heat of vaporization, specific heat capacity, and density. These properties influence the refrigerant’s ability to absorb and release heat efficiently, and thus impact the overall performance and efficiency of the HVAC system. For instance, a refrigerant with a high latent heat of vaporization can absorb more heat energy during the evaporation process, resulting in better cooling performance.