DEHUMIDIFYING AND COMBINED KILNS
If automatic controller is the brain, then the heart of dehumidifying wood drying kiln is a heat pump. Heat pumps are also called dehumidifiers or dehumidifying units for wood drying kilns - which are also known as condensing wood dryers.
Main parts of heat pump are: compressor, evaporator (cold section), condenser (warm section), heat pump fans and finned electrical heaters. Heaters mainly work in the heating stage so that optimal conditions in the kiln are achieved, after which drying process starts.
In the drying stage heaters are rarely or ere not used at all. Air in the kiln passes through the load of timber and absorbs moisture from the wood. Part of that air circulates through the heat pump where the moisture is condensed and drained out of the chamber. This process alone consist of few consecutive stages. First heat pump fans aspirate air from the drying chamber and force it to pass through the heat pump. Moist, damp air pass over evaporator (cold section) first, where the moisture is condensed, and water is collected and drained out of the chamber. The air then passes over condenser (warm part) where is reheated without the use of the electrical heaters. If needed, air can be additionally heated on electrical heaters, but during drying this rarely occurs, so the energy consumption is significantly low. Dried, reheated air comes back to kiln chamber and the whole process starts again.
Environment friendly refrigerant R134a is used for heat pump operation.
Heat pumps are mounted on the 500 mm high chassis, outside the drying chamber next to wall. There are two openings on the wall (lower one for suction of the moist and damp air from the chamber, and higher opening for blowing of dry reheated air back into chamber).
Technical data for heat pumps can be found in the following table:
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