Development of a low-temperature heat-pump grain dryer. Volume I: main body

The development of a prototype low-temperature heat pump grain dryer is documented. Previous developmental work, embodied in a heat pump design code and a first generation heat pump dryer, is reviewed in the context of this research. The developed heat pump design philosophy is reported, and each pertinent step in the design process detailed, particularly the computer-generated sealed refrigerant system synthesis. A new, innovative technique for controlling evaporator frost, while maintaining continuous and efficient drying, is revealed. Also presented is a control system which surmounts the difficulties in heat pump operation imposed by an initially cold grain mass in the dryer volume. Fabrication of the developed heat pump dryer is also documented. Also included are details of a comparative field test of the prototype heat pump dryer and a commercial 24 kW electric resistance dryer. Field test instrumentation, preparation, and supervision are reported. Performance data, acquired during the field test, are presented and comparisons between the heat pump and resistance system are performed. Results of an economic analysis of heat pump grain drying as compared to current and contemplated drying alternatives are presented. Conclusions concerning the future viability of heat pump grain drying are drawn and discussed.