Abstract: A material drying apparatus for removing moisture from material positioned in an envelope interior. The apparatus comprises an inlet structure, an air removal assembly to remove air from the interior, and a moisture removal assembly for removing moisture from gases from the interior. The assembly comprises a first moisture removal structure, a second moisture removal structure, and a heat pump for transferring heat in a selected direction between the first and second moisture removal structures. The heat pump alternately heats a heat exchanger of one moisture removal structure and cooling a heat exchanger of the other moisture removal structures. The apparatus comprises a control apparatus for controlling operation of the first and second moisture removal assemblies and the heat pump. The control apparatus is configured to sense a condition of the apparatus and reverse operation of the heat pump upon detecting that the condition has passed a predetermined level.