Short #3 - Saturation

This short podcast episode is about saturation and what it means. Bryan covers related topics, including boiling, evaporation, and condensing.

Saturation refers to something that is "full" of something else. In science, "saturation" refers to a substance being in the middle of a phase change. (For example, boiling water stays at 212 degrees until it all boils off and becomes water vapor.) In HVAC, we often use the term to refer to refrigerant with liquid and vapor are present at the same time. The refrigerant is typically both liquid and vapor in the evaporator and condenser; phase changes occur in those two components as refrigerant changes from a liquid to a vapor and vice versa.

Refrigerant tanks are contained systems, so the liquid-vapor mix remains at equilibrium, and the temperature and pressure will change at a predictable rate. That is why we can use the P-T chart to determine the refrigerant type; a given type of refrigerant that is changing state at a given pressure will always be a certain pressure.

The process of changing state is where we can utilize so many more BTUs of heat. When a substance is at saturation, that substance will not increase in temperature so long as it remains in its current state. However, that substance will continue absorbing heat until it fully changes its state. We call the added heat that does NOT contribute to a temperature change "latent heat." Evaporators are so effective at absorbing BTUs of heat because refrigerants have relatively high latent heat of vaporization values; it takes a lot of added heat to make a refrigerant change from liquid to vapor.

However, evaporation can occur WITHOUT boiling. Temperature is only the average heat content, and some faster-moving liquid molecules can still break free and become gas.

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