RH%, measure/determine.

There are four methods of determining the relative humidity in the kiln:

• Measure the dry bulb and wet bulb temperature and then use a conversion chart.
• Measure the dry bulb and the depression (difference between dry bulb and wet bulb) and then use a conversion chart.
• Measure the relative humidity using a relative humidity sensor (several models are available with different output signals and sensor accuracy).
• Measure the EMC using a special wafer (similar to measuring wood moisture content).

The first method of using the dry and wet bulb is the most common in the industry today, mainly for historical reasons. However, there are very good arguments for changing to one of the other three methods. (Wooddryer System prefers the relative humidity sensor)

The last three methods are similar in function and they are alike in the way they operate the kiln vents and exhaust system. The biggest problem with the dry and wet bulb method is that when the heat source is disabled, the wet bulb is falling even though the relative humidity is rising. This could result in conditions which promote mold and fungi stain if the heat source is out for a longer period. On the contrary, the other three systems measure the relative humidity related readings and the venting/exhaust continue independently of the accuracy and reliability of the heat source and temperature control. Objectively speaking, it is the ability to independently control the venting without interference from the heat controls that makes the best operational sense.