Saturation can be CONFUSING - Short #159

In this short podcast episode, Bryan explains why saturation can be CONFUSING and clears up some common misconceptions.

Saturation applies to dehumidification and refrigerant inside the system. Generally, saturation is the state at which a substance can no longer hold or absorb any more of another substance. When air is saturated with water vapor and can hold no more, it is at the dew point or 100% relative humidity; it will condense on any surface below the air temperature.

Air isn't like a sponge that absorbs water vapor; saturation deals with vapor pressure, particularly the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases in a closed system. 

Dehumidification is the process by which we remove moisture from the air; this process improves comfort across a significant portion of North America during the summer months, and it prevents fungal growth inside the home. Air in a dehumidifier or an HVAC system in cool mode makes contact with a surface at a temperature below the dew point. So, moisture comes out of the air and condenses on the coil. Colder evaporator coils, which result from longer runtimes, are more effective at removing moisture.

Inside a system, the refrigerant in the evaporator boils as it absorbs heat. The refrigerant can absorb a lot of heat due to the heat required to change state, also known as latent heat (compared to sensible heat, which is the heat required to raise the temperature of a substance). Until the refrigerant completely boils off, it is at saturation. Pressure also dictates the saturation point, and we use refrigerants that can boil under the appropriate temperature and pressure conditions for the HVAC equipment we're working with.

 

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