During an early stage of drying frozen peppers, an electric heater is often used for elevating the temperature of a drying chamber to a certain temperature due to liquid back of the compressor or frosting at the evaporator. Therefore, it is necessary to devise an energy-efficient method to replace or less use electric heaters since they have very low energy efficiency. Also, to shorten drying time, it is essential to rapidly elevate the chamber temperature. In this study, a set of performance tests using hot bypass gas, air dampers, external evaporators, and radiators has been tried to lower the operating temperature of the heat pump dryer as well as to decrease the temperature-elevating time. According to the test results, hot bypass gas is beneficial in increasing the energy efficiency by lowering the initial operating temperature of the heat pump to 3℃. Furthermore, air dampers, external evaporators, and radiators can greatly improve the rate of temperature elevation. When compared with the temperature elevation rate of the standard dryer, 4.1℃/h, an external evaporator can improve elevation rate by 78%, air dampers by 93%, and radiators by 45%.
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