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constant weight is achieved.
Oven: Place the 1” section in an oven at 215ºF (101ºC)
until the section stops losing weight, usually takes
24 hours. Check hourly until the section weighs the
same in separate weighings.
Step 10: Calculate the moisture content of each 1”
section separately using the following formula:
Step 11: Average the moisture content of the two
1” sections from each 28” sample board to calculate
the estimated moisture content of the sample board
when it was cut.
Step 12: Calculate the oven dry weight of the 28”
sample board is using the following formula and the
average moisture content (MC) from the previous
step:
OD weight =(
Wet Weight
100 +%MC
)X 100
Step 13: Write the calculated OD weight on the sample
board so that it is readily available.
Step 14: At about the same time each day, weigh the
sample boards and calculate the current moisture
content with this formula:
Step 15: Place the 28” sample board back in the same
place in the kiln it came from.
Step 16: Calculate the daily drying rate for each
section. Keep all the gures written down as a record
of the load. Make any adjustments to the schedule
based on the fastest drying sample.
Step 17: Once the moisture content of the kiln is below
20%, it is often a good idea to cut new 1” sections from
the center of the sample boards (1 section per board).
Example: Two 1” sections are cut from 30” sample
board 1, and labeled 1A and 1B. They are weighed on
a balance, and the weights are: A=2.5g and B=2.3g.
The sections are placed in a microwave on low power
for 20 minutes and weighed, weighing A=1.7g and
B=1.6g. They are put back in the microwave for 1
minute and weighed again. The weights did not
change, so these values are now oven dry weights.
Calculate the moisture content using the formula in
step 10.
A = [(2.5 / 1.7) - 1] x 100 = 47.06 B = [(2.3 / 1.6) - 1] x
100 = 43.75
Average the two calculations together:
(47.06 + 43.75) / 2 = 45.40%. This is the calculated
moisture content for the rest of the sample board.
Calculate the oven dry weight of the sample board 1.
Use the formula in step 11. The green weight is 1.64
kilograms.
ODW = (1.64 / 145.4) x 100 = 1.13 kg.
After a day in the kiln, weigh sample board 1 and it
weights 1.58 kg. Using the formula in step 13, the
moisture content is:
%MC = [(1.58 / 1.13) - 1] x 100 = 39.8
The daily change in moisture content is:
45.4 - 39.8 = 5.6%.
%MC=(
Wet Weight
Oven Dry Weight
-1)X 100
Current %MC=(
Current Weight
Calculated Oven
Dry Weight
-1)X 100
Drying Rate Index (DRI)
The dry kiln industry has never had a method of
predicting drying rates. This is remarkable as one main
reason for having a kiln is to bring about predictable
production rates. The EMC value gives an end point
of what the moisture content of the lumber would
eventually become but it does not give an indication
of how long it will take to reach that moisture content.
Drying schedules for dehumidication drying were
developed in the late 1970’s. It became obvious that
a method of adjusting kiln schedules to meet drying
time objectives within the limitations of the operation
range of the dehumidiers had to be found.
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