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How Important Is Airflow? The airflow in the kiln chamber is very important. The velocity of the air over the wood affects the drying rate and provides even drying. You should discuss air velocity with the kiln manufacturer to be sure that the air velocity in the kiln will be adequate for the species and thickness of the lumber you are drying and the type of kiln you are using. Generally, wetter lumber requires a higher velocity of air through the lumber. If the air is only blowing through 4 or 8 feet of lumber, the airflow requirements are less. Should The Fans Reverse? Fans usually reverse in larger kilns. This prevents uneven drying by forcing the air to enter the lumber pile first from one direction and then from the other. It also corrects for dead air spots which may result from the way the lumber is stacked. Generally, lumber that is stacked over 12 feet (3.5 meters) deep in the direction of airflow should have reversing fans. If the lumber stack is less than 12 feet thick, reversing the fans will not make any significant difference in the drying. What Type Of Heating System Should Be Used For Initial Warm–up? It is only necessary to heat the kiln to about 85F (29oC) to start the dehumidification process. Once started, the process feeds itself by recycling the heat recovered from the air. Initial warm–up can be done with nearly any type of heating system. Usually, small kilns or single kiln chambers use electric heat, because the additional money required for a more traditional type of heating system doesn’t make economic sense when the heat is only used for a few hours a month. When larger kilns are used or more chambers are added, it may make sense to install a gas, oil or wood boiler to provide heat through steam coils. This is an economic decision based upon local energy costs, weather, type of lumber being dried, etc. Nyle can provide operating cost estimates to help with this decision. However, in most cases, electric heat provides the most economic choice for initial warm–up. Can Pitch Be Set In Pine? When softwoods are dried, pitch sets at the final temperature of the drying cycle. For example, if the last step of drying is 120F (approx. 50C), then the lumber has to be get above that temperature again before the pitch starts to run. Some high-speed sanding equipment used by major furniture manufacturers heats the wood to 160°F, so these manufacturers require pitch set to that temperature to avoid wasting sanding belts. If the pitch must be set, it can be done by heating the lumber at the end of the drying cycle to the necessary temperature. This can be done even if the dehumidifier is not rated to operate at that temperature, because during pitch setting you are not removing water with the dehumidifier, you’re just applying heat. 12PDF Image | INTRODUCTION TO KILN DRYING
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