An optimization procedure for heat pump drying via an air side process parameter, known as contact factor (CF), for single and multi-chamber drying is presented. Dimensionless functional parameters have been developed and studied to correlate the CF parameter. Incorporating these dimensionless parameters to an existing validated tunnel dryer model, an "economic" CF value can be determined, which allows one to optimize the dryer performance through judicious selection of the drying conditions. Optimization algorithms are presented for both single and multi-stage drying to minimize the costs for drying operations.