Diagnosing Window Condensation Using Absolute Humidity
Winter is the time when perplexed, frustrated people across the northern hemisphere contact me complaining of condensation and frost on their windows. The colder or more sudden the cold snap, the worse is their window condensation. Window condensation occurs when water vapor in the air (humidity) is chilled when contacting cold window surfaces. Under “dewpoint” conditions, the water vapor changes from a gaseous state to a liquid state and presto, your windows are wet.
Condensation investigators are hampered by the convention of measuring "Relative" Humidity (RH) because RH is only meaningful when tracked alongside the temperature at which the reading is taken.
When you convert the RH+temperature into Absolute Humidity, much becomes clear. Absolute Humidity is simply the actual amount of water vapor in a given space. When you track AH in a building, you can clearly see where the water vapor is high and where it is low. This may translate into knowing the location of a moisture source, a condensation location and a place of high air infiltration.
Read much more on this subject here: Chicago Window Expert: Diagnosing Window Condensation Using Absolute Humidity