Dew Point

ATMOX Systems operate on the premise of using only drier air from the outside to ventilate the attic or crawl space. How does the system know if the air is drier outside? The webpage on Humidity explains how relative humidity alone cannot be used to determine ventilation. The ATMOX System uses a Dew Point comparison.


Dew Point is the temperature where any air mass when cooled to that temperature reaches 100% humidity.

 

Air with a lower dew point is drier than air with a higher dew point. The ATMOX System uses its sensors to measure both temperature and relative humidity both outside and inside the crawlspace or attic. These measurements allow ATMOX to calculate the dew point in each location and make a true comparison of the air masses.

Humidity vs Dew Point Video
Dew Point Example

Using the same example as on another webpage in looking at humidity:

  • Air Mass A: Air with 45% relative humidity at a temperature of 95 degrees F.
  • Air Mass B: Air with 90% relative humidity at a temperature of 70 degrees F.

 

  • Air Mass A has a dew point of 70 degrees.
  • Air Mass B has a dew point of 67 degrees.

Based on this comparison if Air Mass B was in the crawl space and Air Mass A was outside, then the system would wait to ventilate with fans until conditions improved. 

Now, when the temperature and relative humidity outside change in Air Mass A, the calculations will change.

  • Air Mass A: Air with 90% relative humidity at a temperature of 60 degrees F.
  • Air Mass B: Air with 90% relative humidity at a temperature of 70 degrees F.
  • Air Mass A now has a dew point of 57 degrees.
  • Air Mass B has a dew point of 67 degrees.

Even though Air Mass A has a much relative humidity of 90%, the air temperature has dropped to 60 degrees F. The new dew point of Air Mass A is now 57 degrees and lower than Air Mass B. This would allow the ATMOX System to use outside air to dry.

 

For proper ventilation for moisture control, it takes the ability to compare the air masses to make sure that the outside air being brought in is actually drier, and it requires the proper measurement tool, in this case dew point.