[CAUT] Reading low humidity

[Don]

Hi Ron,

I wonder if anyone has access to the thesis mentioned here:

http://alcor.concordia.ca/~raojw/crd/reference/reference001180.html

and this:

http://theses.lub.lu.se/postgrad/search.tkl?field_query1=pubid&query1=tec_19
8&recordformat=display

Clearly change of moisture content in wood is non linear--and greatly
affected by boundary layers.

Also temperature plays a role for sorption rates are retarded as
temperature drops.

Perhaps this is one reason a null point in a DamppChaser system may not be
desireable?

At 05:18 PM 3/3/2006 -0600, you wrote:
>
>
>> "Wood with very low EMC will absorb ambient high RH very
>> quickly. It's slower to dry out, and it takes higher temps and airflow to
>> speed that process (read institutional conditions <g>). I can measure RH
>> easier than EMC, and RH is good at predicting what will happen in the near
>> and long term future."
>> 
>>         I gain from this that wood reacts very quickly on the intake and 
>> very slowly on the release. 
>
>Not so. I've seen it assumed a lot of times, but have never 
>been able to find documentation to that effect from even a 
>minimally authoritative source. Both absorption and release of 
>moisture in wood is proportional to the difference between 
>wood MC and atmospheric RH%.
>
>Even so, keeping track of RH% readings is a very good 
>practical method of anticipating what the instruments' 
>reactions will be with the resulting MC levels, which are 
>lagging somewhat behind the RH% changes.
>
>Ron N
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Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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