Solar Dry Kiln

A common question among folks that have small portable sawmills is – how can I dry small loads of lumber?   Kiln drying lumber is an excellent means to add value to the lumber and make a small sawmill more profitable.  Many people that are interested in lumber drying don’t want to buy and operate a boiler and don’t feel that their operation is large enough to justify a dehumidification kiln.   Dehumidification drying is an excellent method of drying small to medium quantities of lumber.

Another alternative is solar drying.  A solar dry kiln is simple to construct and operate.  The USDA Forest Products Lab has already done all the research needed on how to build and operate the kiln.  The operator just needs to be aware of a few drawbacks.  First, there will be little to no drying on cloudy days so your total drying time may take longer than other drying methods.  Second, on sunny days you may have excessive drying so it is important to monitor the drying rate and use your fans and vents appropriately.  Solar lumber drying is no different than any other method in that you will need (1) moisture meter, (2) sample boards to monitor moisture drying, (3) scale or balance to obtain weights of your sample boards during drying, (4) a drying schedule.   Below is an excellent publication that summarizes how to build and operate a solar dry kiln.   Let me leave you with a few final thoughts on solar drying.  It is very important to understand that lumber can dry very fast or very slow in a solar kiln.  It can dry so fast that drying defects such as warp and case hardening develop.  Green wood that is put into a solar kiln has the potential to develop surface mold if the initial drying rate is too slow.  

DESIGN AND OPERATION OF A SOLAR-HEATED DRY KILN FOR TROPICAL LATITUDES

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