When does the exchange of BTUs become greatest in a cooling system?

The exchange of BTUs in a cooling system occurs most efficiently when there is a low evaporator temperature combined with a high condenser temperature. This configuration allows the refrigerant to absorb a greater amount of heat (BTUs) from the environment as it evaporates in the evaporator section, while simultaneously rejecting that heat effectively in the condenser section.

In a cooling system, the evaporator's primary function is to absorb heat from the space being cooled. When the evaporator temperature is low, it allows the refrigerant to absorb more heat because a larger temperature differential exists between the evaporator and the indoor air. Meanwhile, a high condenser temperature facilitates the rejection of heat from the refrigerant to the surrounding environment, as it maintains a greater difference between the refrigerant's temperature and that of the outside air or water.

In summary, this combination of low evaporator temperatures and high condenser temperatures optimizes the heat exchange process, leading to more efficient cooling operation and maximizing the BTU exchange in the system.