A moisture removal system having a crop drying enclosure for holding a crop product to be dried. A closed loop air circulation system is provided which includes a moisture removal enclosure for removing moisture from circulating air along with air ducting operatively connecting the moisture removal enclosure to the crop drying enclosure air inlet to form a closed loop moisture removal air system. A heat pump system, including a compressor, a first heat exchanger capable of operation as a condenser, along with two additional heat exchangers, each capable of operating as either a condenser or evaporator are positioned within the moisture removal enclosure, to remove excess moisture from the circulating air without the addition or extraction of heat from the ambient air temperature.