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A heat pump dryer can save more energy than other dryers since its drying efficiency is 2~3 times higher than that of other types of dryers. However, the lower bound of evaporating temperature for an R134a heat pump cycle ranges from 5 to 10°C; when the outdoor air temperature closely approaches the evaporating temperature, it experiences reduced efficiency and ultimately becomes inoperable. To address this issue, a cascade heat pump dryer equipped with a solar collector was considered in order to examine the operability and efficiency of the heat pump cycle, depending on changes in the outdoor air temperature in wintertime. The changes in cascade cycles, depending on the temperature in a drying chamber, were also observed. The results showed that the average COP of the cascade heat pump dryer was approximately 2.6 under the temperature range of -10 to 20°C. An electrical heater whose COP is less than 1 should be used in that temperature range. It was also found that COP of the dryer increased by approximately 35% when using a solar collector under a low outdoor air temperature environment.
PAPER REVISED: 2017-01-26
PAPER ACCEPTED: 2017-02-22
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THERMAL SCIENCE YEAR 2018, VOLUME 22, ISSUE Issue 2, PAGES [993 - 1001]
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© 2024 Society of Thermal Engineers of Serbia. Published by the Vinča Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Belgrade, Serbia. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International licence