How to Use: Step 3

    Interaction of T, RH and DP
   Preservation Evaluation
   Examples

To regulate the RH %, there are two options:

1. Humidify the air (Increase the Dew Point)
Notice the different preservation consequences of the two options. Both increase the RH, but:

#1. Requires MORE energy (to humidify the air) and receives only an OK rating for Natural Aging.

#2. Requires LESS energy (to heat the air less) and receives a GOOD rating for Natural Aging.

The PI of #2 is 3 times greater than the PI of the original scenario and 5 times greater than the PI of solution #1.

2. Heat the air less (Decrease the Temperature)
Example: Managing Winter Dryness

Help plan, evaluate, and manage storage environments with respect to preservation benefits, preservation risks, or the realities and capabilities of your system.

Managing Winter Dryness
A commonly-encountered preservation problem is excessively low indoor RH during winter. In cold climates, the outdoor dew point can become quite low, averaging 15oF (-9oC) for several months. At this dew point, there is very little moisture present in the air. Normally, it can be assumed that the dew point of outdoor air is approximately the same as indoor air, unless the indoor dew point has been artifically raised (by a humidifier) or lowered (by a dehumidifier).

Winter Dryness

The Dew Point Calculator helps understand what the consequences for indoor RH might be from such a low outdoor dew point.

  1. Go to the Dew Point Calculator
    2.
  2. Click to Solve for % RH
    3.
  3. Move the Dew Point slider to 15oF (-9oC)
    4.
  4. Move the Temperature slider to a human- comfort temperature (70oF).
    5.
  5. Observe the % RH levels as the Temperature increases
    6.

The result of heating outdoor air with a dew point of 15oF to a human-comfort temperature of 70oF is to drive the indoor RH to a very low value - 12%. Note the very low EMC of 2.9%. If this condition persists over several months, objects may be damaged due to shrinkage and brittleness.