How are VacDry vacuum kilns more energy efficient, and save me money per kiln charge?
Conventional kilns skim water molecules off the surface of wood by moving warm and dry air across the wood. Drying must be done very slowly to allow time for water molecules to migrate to the surface. It is very easy to over-dry the surface and cause case-hardening and cracks. In a conventional kiln, the longer your kiln schedule, the longer those circulation fans are running and the more heat and steam that ends up vented to the great outdoors.
Other vacuum kiln manufacturers have believed incorrectly that the lowered boiling point of water would make drying fast and wood spare the wood of any drying degrade. To a small degree, this has been true.
In a VacDry vacuum kiln, only two small energy efficient water pumps run continuously. The main drying force of the vacuum pump only runs when needed. Just as significant, vacuum is a great insulator and the wood is in direct physical contact with the heat source: practically every BTU that enters the kiln chamber is used to directly evaporate water, which tremendously increases efficiency. Convective losses are practically nonexistent, conductive losses are very minimal, and the naturally minor radiant losses are kept in check with a small amount of insulation.
VacDry Kilns are the only that use a property of water called vapor pressure. When water’s vapor pressure equals ambient (surrounding) pressure, water boils. An example is water at sea level. Pressure is measured by a column of Mercury which is measured in “Torr”. At sea level, the atmospheric pressure is 760 Torr. If you heat water to 212’F, the vapor pressure is 760 Torr and the water boils. The water changes from a liquid to gas. In addition, the water can’t be heated above 212’F. A hotter burner will increase boiling but the water stays at 212’.
VacDry uses precise control of the vapor pressure of the water in the wood. This is combined with precise control of pressure in the vacuum chamber. The result is perfectly controlled drying. We can chose the fastest rate that the wood will give up water.
Since VacDry is using a pressure gradient instead of a humidity gradient, VacDry can boil away water from beneath the surface of the wood. This eliminates the moisture gradient that results in surface and end checks with conventional methods. The result is beautiful and stress free wood.