How to Use: Step 1

Interaction of T, RH and DP

Preservation Evaluation

Examples

Definitions: Temperature: A measure of heat energy, expressed in degrees Fahrenheit (F) or Celsius (C). Relative Humidity (RH): A measure of the relative saturation of the air with water vapor, expressed as a percentage from 0 to 100. Dew Point: The temperature at which water will begin to condense out of the air, expressed in degrees F or C. While RH is the relative saturation of the air (based on the temperature), dew point expresses the absolute moisture content of the air. With no humidification or dehumidification of the outside air, the indoor dew point will be the same as the outdoor dew point.

Dew Point determines which Temperature will give you which RH. Dew Point measures the absolute moisture content of the air. Therefore, it determines how much moisture you have to add or subtract (humidify or dehumidify) to achieve the appropriate RH in your storage environment.

Interaction of Temperature, Relative Humidity, and Dew Point

View the interaction of temperature, RH, and dew point. Learn to control one variable (For example, RH) by controlling another (for example, temperature).

What do Temperature, RH, and Dew Point mean for an environment?
Every environment has exactly one combination of temperature, RH, and dew point. If you change any of these variables, you will have a different environment

How are Temperature, RH, and Dew Point related?

• At constant temperature:
  RH and Dew Point will increase/decrease together
  
  
• At constant RH:
  Temp and Dew Point will increase/decrease together
  
  
• At constant Dew Point:
  As Temperature increases, RH will decrease
  As Temperature decreases, RH will increase

Why are Temp, RH, and Dew Point important for preservation?
The processes of decay are profoundly influenced by environmental conditions. A proper environment can prevent damage, and an improper environment can cause damage.

Temperature and RH determines the preservation quality of your storage environment.

Temperature is the most significant determinant of the rate of chemical reactions within the organic materials of your collection objects. In other words, Temperature determines how fast (or how slow) organic materials will "naturally age".

Related Preservation Metrics:
TWPI and PI

Relative Humidity determines how much moisture your collection objects will contain. High RH will leave objects too damp, while low RH will leave objects too dry.

Related Preservation Metrics:
% EMC and % DC