For practical purposes, what does the low side of a refrigeration system encompass?

The low side of a refrigeration system primarily encompasses the components where the refrigerant is at low pressure and low temperature. This is crucial for understanding how the refrigeration cycle operates. In this context, the evaporator is the correct answer because it is the component where the refrigerant absorbs heat from the environment, causing it to evaporate and change from a liquid to a vapor. This process typically occurs at lower pressures, which is characteristic of the low side of the system.

While the compressor, condenser, and expansion valve are essential components of the refrigeration cycle, they do not fall under the "low side" category. The compressor, for example, is part of the high side, as it increases the pressure of the refrigerant after it leaves the evaporator. The condenser also operates on the high side, where the refrigerant releases heat to the surroundings and condenses back into a liquid. The expansion valve regulates the flow of refrigerant into the evaporator, but it functions between the high side and the low side rather than being fully part of either. Thus, understanding these roles clarifies why the evaporator is the main component of the low side in refrigeration systems.