Study On Optimal Control Strategy Of Solar Air Heating System

With the rapid application of solar technology in building, the using of solar air collector were universally accessed in the construction area. The thermal performance of solar air collector was affected by the unstable outside weather condition, thus influencing the thermal performance of the passive solar energy building.Therefore, the analysis of thermal performance and control strategy of solar air collector are necessary. Recently, many researchers have tried to optimal control of solar air collector by various control strategy, yet have not combination considered the influence of parameters and energy consumption. In this thesis, the numerical model of Wall-mounted Solar Air Collector (WSAC) proposed by our research team and the control strategy developed by fuzzy logic were studied.Firstly, the thermal properties under different flow rate of WSAC was explored by both experimental and theoretical study. Heat transfer model of WSAC and passive solar energy building are developed by FORTRAN, combined with an solar energy transient simulation system -TRNSYS, and validated by field experiments. Based on this model, the solar irradiance is identified as the greatest impact factor of WSAC. Meanwhile, the effect of solar irradiance, flow rate, inlet air temperature on WSAC instantaneous thermal and net efficiency are explored. The conclusion is:considering the case of fan power consumption, with the increase of the flow rate, the difference between the net efficiency and the instantaneous thermal efficiency is increases. Especially, when the solar irradiance are about 300 W/m2 and 650 W/m2, respectively, the net efficiency are lower than the instantaneous thermal efficiency by 12.7% and 3.8%, respectively, with the flow rate of 154m3/h.Then, based on the above research, we study the variable flow rate control strategy of WSAC, and compared several different control strategies, including intermittent operation, continuous operation, and variable flow operation. The results showed that the net efficiency of variable flow operation are greater than intermittent operation, continuous operation. The energy saving of variable flow operation mode A reached 37% compared with variable flow operation mode B.Finally, with the established of the passive solar house with WSAC simulation platform, the net efficiency and energy consumption of variable flow rate control strategies were studied by fuzzy logic. The results show that the control strategy based on the changes of solar irradiance gain the most energy conservation, yet the indoor temperature fluctuation is greater than other approach, and during the daytime the highest temperature is up to 31℃; the control strategy based on indoor temperature gain the worst energy efficiency. Meanwhile, when exploring a continuous distribution rules fuzzy logic controller, we found that the optimal of the membership functions and fuzzy rules of fuzzy logic controller could improve the control precision, and could be used to simulate more conditions of the control strategies.