| As a big country of tobacco producing and consuming in the world, coal is widely adopted by way of curing for a long period of time in china.The increased coal consumption of energy and environmental stress in tobacco curing cause finding new ways to energy saving and emission reduction. As a new technology, heat pump drying is a gradually mature and green environmental protection, but its research in the field of tobacco curing is far from perfect.Domestic and external researches of the heat pump in the drying field mainly focus on two aspects, which are improving heat pump’s performance and combined heating with auxiliary heat source. It has achieved some great results in improving the heating performance of heat pump by improving the control method, the application of efficient drying medium, chemical heat pump, absorption heat pump. A great progress is also made in combined drying and auxiliary solar energy research. Due to dehydration in the curing process, the research on heat and humidity recycling is also constantly updating. It ranges from the partly hot air circulation to cascade utilization of air with heat and humidity; from simple heat exchange by a heat exchanger to heat and humidity recovery by heat pump units; and nowadays developing into bulk tobacco house group of combined heating.Previous study has a few deficiencies. Some researches have laid emphasis up on the effects of single factor on heat pump heating performance, weaken the influence of other factors in the working condition of heating effect. Most of the researches of the evaluation drying system are based on the cost of producing 1 kilogram dry leaf tobacco, which is difficult to accurately characterize comprehensive performance of system.Embarking from the actual curing process, this paper, compared with coal-burning curing, explored the energy saving benefit of heat pump and heat and humidity recovery technology, analyzed the influence factors of heating by heat pump, put forward the performance formula of the heat pump units to meet the requirements of curing process. Testing platform was established in Wushan, Chongqing, and mutually confirms the simulation calculation results.Firstly, it was established that energy consumption models of two bulk curing barns and the results of simulating calculation was compared. Two numerical models with fresh tobacco leaf load amount of 4000 kg were established in Shapingba District, Chongqing based on the DeST software, one of which was insulated bulk curing barn heated by heat pump with heat and humidity recovery system, and the other of which was bulk curing barn heated by coal.The dynamic load calculation showed that the heat load peaks of insulated bulk curing barn heated by heat pump and bulk curing barn heated by coal are 32.78 kW and 37.60 kW.Apparently the heat load peak reduced by about 15.4% after the application of insulation material in bulk tobacco barn, and it played a positive role of reducing the unit capacity and increasing the hourly load rate. Further energy consumption calculation showed that the average energy consumption for each curing of insulated bulk curing barn heated by heat pump was 628.04 kW?h; the average energy consumption of bulk barn heated by coal was 260.00 kW?h and coal consumption was 573.34 kg. Taking price level in Chongqing into comsideration, the costs(including artificial management fee) of these ways were 263.49 yuan and 475.07 yuan, which stated cearly that the energy conservation and emissions reduction effect of insulated bulk curing barn heated by heat pump is more remarkable than heated by coal. Through the dynamic payback period method, it demonstrated that the payback period of insulated bulk curing barn heated by heat pump is 3.96 years. The best improvement of bulk curing barn heated by coal is discussed by using the method of economic life and it proved that upgrading to insulated bulk curing barn heated by heat pump was an optimal choice, of which the economic life lasted,the longest, 18 years. The average energy consumption of heat pump with or without the heat and humidity recovery system is 628.04 kW?h and 785.19 kW?h respectively; which illustrated that a heat pump with heat and humidity recovery system can save electricity about 25.02%. It not only saved energy, but also guaranteed the tobacco quality. With the comprehensive performance of drying system evaluated by SMER, it showed that SMER of insulated bulk curing barn heated by heat pump was 29.30%, higher than heated by coal. The comprehensive drying performance of insulated bulk curing barn heated by heat pump had an obvious advantage.Secondly, it was analyzed that the influence factors of heating performance by heat pump. In order to eliminate the effect of indoor temperature and humidity control, the constant indoor temperature and humidity was set to analyze factors which influenced heat pump unit’s heating performance. It became apparent that loading rate and outdoor temperature are factors correlated with COP of heat pump unit positively. The impact of outdoor temperature on COP was greater in leaf drying stage than in yellowing stage, and was the greatest in stem drying stage. Otherwise, loading rate was closely related to the unit COP in whole curing process. "Three times ten coefficient" fitting among unit COP, loading rate and outdoor temperature in those three stages respectively. The fitting formula achieved with high correlation coefficient, and the effects matched great.Thirdly, it was assessed that the energy consumption characteristics of the experimental tests. Experimental results showed that the cost of producing 1 kilogram dry leaf tobacco in insulated bulk curing barn heated by heat pump was 1.11 yuan and saved 63% curing cost compared with 2.97 yuan which was the cost of bulk curing barn heated by coal. Contrasted with the bulk curing barn heated by coal, dynamic payback period of insulated bulk curing barn heated by heat pump was 4.02 years.Finally, the simulation calculation was contrasted with experimental test results. Through hypothesis testing, it was analyzed that the unit’s heating performance between simulation calculation and experimental test. It turned out that the simulation formula matched test results well under the significant level of α= 0.05.The comprehensive performance of drying system in simulation calculation and in experimental test was evaluated by specific moisture extraction rate(SMER) index. The results showed that the comprehensive performance of insulated bulk curing barn heated by heat pump was better than bulk curing barn heated by coal and the relative error was about 14.7%, which indicated the simulation calculation was in conformity with experiment results. After analyzing the differences between simulation and experiment, it resulted from the different outdoor temperature resulting in different heat dissipating capacity of the building envelope in bulk curing barn heated by coal, however it attributed to the different conditions(different factors such as loading rate and outdoor temperature, etc.)leading to differences of unit’s heating performance in bulk curing barn fuelled by heat pump. |
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