Investigation of a solar assisted heat pump wheat drying system with underground thermal energy storage tank

Abstract

Storage of solar energy in underground Thermal Energy Storage (TES) tank during sunny days and extraction of the energy in the TES tank and its surrounding ground by a heat pump through the year for drying systems is an attractive subject for effective use of solar energy and ground as heat sources. It is possible to store solar energy in the TES tank and ground to use it for heating systems. In this study, modeling of a wheat drying system with a heat pump and underground TES tank charged by solar energy is developed using energy analysis of the drying system to investigate its long-term performance parameters. The drying system has four components, which are wheat dryer, underground TES tank, solar collectors, and a heat pump. The analytical model consists of a solution of unsteady heat transfer problem around the TES tank and energy expressions for the other components. A MATLAB code is developed to examine the performance parameters hour by hour along the years. These parameters are water temperature in the tank, Coefficient of Performances for the heat pump (COP) and system (COPs), Specific Moisture Evaporation Rate (SMER), and energy fractions for the system. When wheat mass flow rate and Carnot efficiency are selected as 50 kg h−1 and 40% respectively, collector area, TES tank volume, COP, COPs and SMER are 70 m2 and 200 m3, 4.43, 4.3 and 6.05 respectively when the system attains periodic operation time from the 5th year onwards for 10 years of operation.