Editor's note: This is the final installment of a three-part series.
Read Part 1.
Read Part 2
In 1998 I left the furniture manufacturing company I was employed at and began consulting to the woodworking industries, mostly in the areas of predrying and kiln drying.
Setting aside conventional drying technique, I considered the physics of drying lumber and developed Alternate Heat/Dump Cycle (AHDC) for lumber and began introducing it to several kiln drying operations. After a brief learning curve, all those using this method of drying had great success. In fact, the manager of one large company declared, “We have been drying lumber the wrong way all these years. Why did no one tell us about this drying technique 20 years ago?” This is a typical reaction from those that adopt AHDC, and none of them would return to their old conventional drying method.
What is AHDC?
It is, quite simply, a technique that dries lumber with a period of heating (during which no venting occurs) followed by a period of intense venting, or Dump Cycle, during which there is no heat or spray. To fully understand why or how it works, you would need to see the PowerPoint presentation that I have prepared. You might think that I am just trying to promote my consulting visit to your plant, but understanding the theory requires an intensive two-way discussion and would become too wordy for a written presentation.
Even though you can apply AHDC without fully understanding the theory, you will eventually want to innovate and make some changes within the AHDC drying technique, so understanding the fundamentals is essential. Just as all lumber has different drying characteristics and no two kilns dry exactly the same, AHDC drying technique is constantly evolving to address these differences. Though the basic AHDC technique is essentially the same for all applications, small, innovative alterations allow it to be customized to fit an individual company's lumber and kilns for best results. It is not just a “one size fits all” technique.
AHDC can be applied to most dry kilns with little or no alterations to the kiln. However, some computer based kiln controllers tend to make it difficult to execute AHDC with their unnecessary protocol that requires certain conditions to be attained in a defined period of time or they shut the kiln down and go into an alarm mode. A few kiln operators using these controllers have been able to work around these over-controlling features and apply AHDC successfully. I encourage each kiln operation to try AHDC manually, using existing equipment, to make sure that they understand its requirements and to assure the desired results. Only after they convince themselves that this technique produces better quality and reduces energy usage would I advise them to consider adding effective powered vents (if they don’t already have them).
For those companies that wish to further automate the AHDC technique, I can recommend two industrial controller manufacturers (neither is a kiln manufacturer) who have developed and installed computer-based controllers that automatically execute AHDC.
AHDC requires specific on-site training and follow-up communications between the kiln operator and the trainer (that’s me). The follow-up communication is critical and included in the original cost of my consultation visit, so most kiln operators contact me daily during the first several weeks following my initial visit and less often as they gain confidence in their ability to apply AHDC effectively and efficiently. Still, most kiln operators contact me at least a few times per year with questions/comments (especially when drying a new species or thickness) and often with recommendations for improvement in schedules. I am in a continuous learning mode, contacting those using AHDC to offer improvements.
Even if you choose not to adopt AHDC drying technique at this time, I encourage you to look at the energy wasted during conventional drying, especially during venting. A few simple changes will allow you to begin reducing this unnecessary waste and, even during these challenging times, allow you to reduce your lumber drying costs. What do you have to lose? More importantly, see what you have to gain?
 Certain rare conditions may require brief periods of venting during the initial drying stages, usually only during the first 24 to 48 hours.Known as “The Kiln Consultant,” Dennis Clay has more than 20 years of hands-on experience drying lumber and managing the drying operations for a large furniture company. As a consultant, he conducts analysis of current lumber handling and drying practices as well as on-site kiln operator training. For information, contact him at firstname.lastname@example.org
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