Monitoring System Design For Solar-Assisted Heat Pump Drying And Performance Test

Energy consumption depends on many factors such as population increase andeconomy rapidly development.It is well known that drying is an energy-intensivetechnical process. It reported that about12%of the total energy consumed byindustrial dryers. In manufacturing processes where drying is needed, the cost canreach up to60-70%of the amount. Thus, one of the biggest challenges is how todecrease the energy consumption on condition that of high-quality products. Heatpump drying (HPD) is energy-efficient due to its exhaust heat recoverable technology.However, single heat pump drying usually consumes high-grade electricity whichproduced from lots of fossil fuel. Solar energy is clean and renewable, solar-assistedheat pump drying (SAHPD) can not only contribute to energy conservation andemission reduction, but eliminate both defect and complement each other’sadvantages.HPD is a coupling process combined with drying medium and heat pumprefrigerant circulation. The drying is much related with several parameters such astemperature and relative humidity. Therefore, it is necessary to monitorabove-mentioned param. A monitoring system for HPD was proposed after theresearch of HPD measurement and control system based on microcomputer or PLCand PC.A set of online monitoring system for HPD based on LabVIEW was studied anddesigned. It consisted of master laptop, CompactDAQ platform which inserted withNI9205analog input module and DS series transducer of temperature and relativehumidity. The online monitoring system features real-time measuring，visual displayand data auto-saving. The system merits include strong expandability，portability andinterface friendly, etc.The online monitoring system was then installed on the original green house-typesolar-assisted heat pump dryer. The experimental device can conduct both HPD andSAHPD tests under the sunny or cloudy day respectively. The cotton and ternip werechosen as the raw materials. The performance test of HPD and SAHPD were carriedout two times each. The cotton and ternip are14kg and10.5kg, dried2hours and5hours respectively. The experiment results are that the biggest moisture removal ofcotton under SAHPD and HPD are6.15kg and4.45kg, and the figures for ternip are8.7kg and7.5kg. The biggest SMER of cotton are1.66kg/kW·h and1.31kg/kW·h inthe two drying methods, while the ternip’s SMER are0.95kg/kW·h and0.88kg/kW·h. Moreover, in the first2hours’ ternip drying, the moisture removal reach up to5.4kgand3.55kg, and SMER are1.44kg/kW·h and1.023kg/kW·h.The experiment results demonstrate that MER of SAHPD increase more than40%compared with HPD under the same material quality and2hours’ drying. It isthus clear that SAHPD is more time-saving. While the SMER of SAHPD increased byover30%. It is apparently that SAHPD is more energy conversation, in other words,SAHPD with prominent energy-saving effect can process more wet material withrespect to the HPD under the same energy consumption.