Relative Humidity and Dewpoint

Imagine a mobile salon as a small saltwater tank. Every action we take within this confined space can significantly alter its environment, much like how even small changes in a saltwater tank quickly affect its chemistry.

Key Concepts: Relative Humidity (RH) and Dew Point

Relative Humidity (RH):

• Measures the actual amount of water vapor in the air relative to the air's temperature.
• Expressed as a percentage.
• Represents the ratio of the current water vapor to the maximum water vapor the air can hold at that temperature.

Dew Point:

• The temperature at which water vapor condenses into liquid.
• Referred to as the frost point when temperatures are below freezing.
• Occurs at 100% relative humidity.
• Influenced by air temperature.

Practical Applications in a Mobile Salon

1. Condensation on A/C Shroud and Walls:
   • If water is condensing on the A/C shroud, it indicates that the unit is too cold and not moving enough air. This causes the plastic to be colder than the dew point of the air in the salon.
   • Similarly, in winter, cold walls can condense when they are below the dew point of the warm, humid air inside. Running a space heater overnight can help warm the walls above the dew point, preventing condensation.
2. Managing Relative Humidity (RH):
   • In high RH conditions, run the A/C on high between stops to reduce humidity.
   • When opening the door with the A/C on the coldest setting, the warm, humid outside air can condense on all cold surfaces inside the salon.
3. Drying Efficiency:
   • Moving air through the coat will dry it until the air hits 100% RH. Without extra heat, drying will stop once the air reaches 100% humidity.
   • A hotter dryer dries faster because warmer air can hold more moisture. However, it will also increase the overall air temperature over time.
   • Additionally, hot air speeds up drying by providing the thermal energy needed for evaporation. 

Tips for Optimal Humidity Control

• To lower RH, use the A/C or an exhaust vent. However, avoid using the exhaust vents if it's hot and humid outside.
• Do not run the A/C and the exhaust vent simultaneously.
• Maximize heat and airflow to minimize drying times. This is essential as higher RH slows down drying due to the air's reduced capacity to accept more moisture.

The graphic above demonstrates the principles of dew point and RH. Your AC moves warm, humid air over cold coils that are below the dew point. This action causes excess moisture in the air to condense out of the air. The air blowing out of the AC will be colder and at 100% RH. Any heat sources inside the van will then warm this air, allowing it to accept more moisture.

Additional Considerations

• The air's capacity to hold water increases with temperature. In a mobile salon, if the air temperature drops to around 68°F, using a heater intermittently can help maintain comfort and assist in lowering the RH.
• Monitoring the dew point and relative humidity can provide insights into the salon's climate control efficiency. For example, if the salon's air is 67°F with 52% RH, the dew point is 49°F. When drying, if the air temperature rises to 72°F with 82% RH, the dew point becomes 66°F, making it easier for the A/C to remove moisture.
• The higher the dewpoint, the easier it is for the A/C to remove moisture from the air.

By understanding and managing these factors, you can maintain a comfortable and efficient environment in your mobile salon, preventing unwanted condensation and optimizing drying times.