The main focus of this paper is the application of a loop thermosyphon (LTS) as an energy saver for a heat pump dryer (HPD) system. The methods involve design, construction and experimental works to study the performance of the heat pump dryer with and without LTS. The conventional heat pump type dryer (without loop thermosyphon), the performance of the loop thermosyphon and the heat pump dryer with loop thermosyphon as an energy saver are experimentally investigated. The experimental results were compared. The economics of a loop thermosyphon for use in heat pump dryer were also analyzed. The amount of longan in one batch was whole longan 120 kg. The specification of the heat pump dryer was the condenser of 8 kW, the evaporator of 5.25 kW and the compressor of 2.75 kW. The size of the LTS can be simulated by numerical simulation method. For this research, the loop thermosyphon was deigned base on the size of evaporator of heat pump. From the result, it can be concluded that the the loop thermosyphon can reduce the specific energy consumption of heat pump system from 12 to 20%, depending on the operating conditions. The average effectiveness of the LTS was 0.20. Application of the loop thermosyphon in the heat pump dryer is beneficial, because the economic analysis shows that the pay back period is about 3 years and the internal rate of return (IRR) is about 30%. These results were obtained by operating the heat pump dryer at an airflow rate of two to four times of the optimum value. For this research, the optimum value is 450 m~3/h. If operated at the optimum value of airflow, the value of energy saving will be more, the pay back period could be less than 3 years and the IRR will be higher than 30%.
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