Why does a reduction in saturated suction temperature (S.S.T.) cause a decrease in cooling system capacity?

A reduction in saturated suction temperature (S.S.T.) leads to a decrease in cooling system capacity primarily because it affects the properties of the refrigerant in the evaporator. When the S.S.T. decreases, it results in an increase in the specific volume of saturated vapor. The specific volume is the volume occupied by a unit mass of the refrigerant; therefore, as the specific volume increases, it means that the vapor takes up more space and becomes less dense.

In cooling systems, the capacity is generally related to the amount of heat absorbed by the refrigerant as it evaporates in the evaporator coils. When the vapor is less dense due to the increased specific volume, the amount of refrigerant that can effectively transport heat decreases. This results in a reduction in the overall cooling effectiveness of the system, translating to lower cooling capacity.

Consequently, if the evaporator struggles to effectively absorb heat from the environment due to changes in the specific volume of the refrigerant, the system's performance diminishes, which is crucial for understanding the thermodynamics involved in refrigeration and air conditioning processes.