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DIFFERENT TYPES OF KILN DRYING What Is A Solar Kiln? There are several types of solar kilns, but they all generally rely on some type of solar collector to provide the heat energy that evaporates the water in the lumber. Unlike solar heating for an office or home, in lumber drying it’s not possible to reduce the heat requirement to the point where solar heating can be competitive. When you’ve got a certain amount of water to remove from a certain amount of wood, you need a certain amount of total heat to do it, and that heat requirement can’t be changed. Drying times in a solar kiln are dependent upon the weather, and thus unpredictable. In hot climates they can degrade lumber due to excessive drying. In colder climates they are unreliable and slow. Solar kilns often use electric–powered fans to circulate air through the lumber, but the cost of running these fans is high—and because of the long drying times, you’ve got to run the fans for a long time, making solar drying quite expensive. The electricity for running the fans in a solar kiln is usually more than would be used running a DH kiln, as the drying time is longer. What Is A Conventional Kiln? A conventional kiln uses heat provided by either steam or hot water coils or a furnace to heat the kiln chamber and remove water from the wood. The water removed from the wood is turned into water vapor by evaporation, and then exhausted from the kiln with the heated air. This process takes a great deal of heat and requires constant heating of air, so these systems are not as energy efficient as dehumidification kilns. To remove one pound of water from the lumber, a conventional kiln has to draw in about 400 cubic feet (or 12 cubic meters) of air, heat the air, and then exhaust it with the evaporated water. Between heating these large quantities of air and heating the water to evaporate it, conventional kilns have a very high heat requirement. They can provide a very good quality of lumber if a good method of kiln control is provided, but their energy consumption is much higher than that of a dehumidification kiln. What Is A Vacuum Kiln? The temperature at which water boils is determined by atmospheric pressure. The higher up a mountain you go, the less pressure the atmosphere exerts, so water boils at a lower temperature up the mountain than at its base. Vacuum kilns take advantage of this fact to achieve drying times that are usually only a fraction of the time required for conventional or dehumidification kilns. A major drawback of vacuum kilns, however, is that the chambers are small, so the kilns cannot dry large quantities at any one time. It is necessary to provide heat to the lumber continuously in a vacuum kiln. To do this, some systems use electric blankets in contact with 9PDF Image | INTRODUCTION TO KILN DRYING
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