Experimental and theoretical assessment of a solar assisted heat pump system for in-bin grain drying: A comprehensive case study

A novel solar assisted heat pump (SAHP) system for in-bin grain drying was proposed to solve the problems of poor uniformity and long drying time of grain in depot with higher initial water content in high grain piles. The effects of different operational parameters on the drying performance were numerically and experimentally investigated. The experimental results indicated that the thermal efficiency of the solar collector and the COP of the heat pump reached 63% and 5.03 under given conditions. The average heating capacity of the SAHP system was 130.2 kW, consistent with the simulation results under a typical sunny day in winter. The average water content of 3,760 tons of grain dropped from 12.9% to 12.5% after 42 h of drying. The specific moisture extraction rate of the proposed system and the exergy efficiency of the grain bin were 1.934 kg/kWh and 40.27%, respectively. The operating cost of SAHP grain drying decreased from 5.57 $/t to 1.43 $/t compared with the grain drying machine for the same drying weight. The daily drying capacity increased from 166 t/d to 334 t/d compared with the mechanical ventilation drying for the same water content reduction rate. This investigation provided guidance for expanding future researches on the SAHP system applied for in-bin grain drying.