Difficulty with Drying Small Loads

      Running a predryer with a quarter charge of green wood is tricky to manage and full of risks. April 24, 2014

Question
We have a 420,000 board foot pre-dryer that is empty. Does anyone see any problems putting in one charger of 70,000 board foot of green 8/4 red oak? I am concerned with holding the depression.

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
I would be concerned too.



From contributor T:
I think you have to watch the RH and loss per day very closely. I also wouldn't run the fans all the time and if need be I'd put some 4/4 oak in with it as well to help control the RH. Gene, what do you recommend for temp in the pre-dryer and do you have suggestions for run times of the fans?


From Gene Wengert, forum technical advisor:
Each pre-dryer has characteristics that need to be understood and accounted for before I suggest the conditions. Certainly a key is uniformity of air flow and the performance of the control system. For the fans, I could imagine cases where we need 50% on for the first two weeks. Temperatures should be as low as possible - as low as 85 F. If the equipment will maintain a constant temperature at that level then varying temps are bad. Then use an RH to give a safe drying rate in the fastest drying region.


From Contributor K:
What does holding the depression mean? I am new to these references.


From Gene Wengert, forum technical advisor:
The depression is the difference between the dry bulb and wet bulb temperatures. It can be used to calculate the relative humidity (RH). To hold the depression means to keep the RH as high as required.


From contributor K:
I would be very cautious about attempting to pre-dry a single charge of 8/4 RO in that manner. You will have to control your drying rate with fan run time-maybe full fan for a few days on wet/green then gradually wind it down to as little run time as 60 minutes on/180 minutes off. The RH will be difficult to maintain with not having the unit loaded. This is what you rely on in a pre-drier for moisture. I utilize fan timers. Otherwise it is very labor intensive to do it accurately unless you want to camp out at your pre-dryer. I find that temps near 70 degrees F are much more satisfactory and forgiving on the drivers, boilers and the building itself here in the northeast in winter. Even in the summer seldom go above 80 degrees.



Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?


Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Primary Processing

  • KnowledgeBase: Primary Processing: Air Drying Lumber

  • KnowledgeBase: Primary Processing: Kiln Operation


    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.



    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB











  • WOODWEB - the leading resource for professional woodworkers


      Home » Knowledge Base » Knowledge Base Article