Design and evaluation of combined ventilation system with air supply and exhaust ducts for a nursery heating piggery in winter

Abstract: Current ventilation mode needs to be updated in a nursery piggery, due mainly to the uneven distribution of airflow derived from the great contradiction between ventilation and heat preservation under the relatively low temperature of the cold region in winter. The previous investigation on data collection found that the relative humidity and the concentration of CO2 generally exceeded the standard value in a nursery piggery. Therefore, the main challenge was how to efficiently supply fresh air. In this study, computational fluid dynamics (CFD) was used to simulate the airflow field in the nursery piggery under the combined ventilation system of air supply and exhaust ducts. The diameter of the duct was 0.3 m. The wind speeds of air supply and exhaust were set at 0.5 m/s and 1 m/s, respectively. The results revealed that the circulation ventilation was formed between the air supply inlet and exhaust outlet. The wind speed was maintained between 0.1 m/s and 0.2 m/s in the cement floor area where the piglets live. An even distribution of air flow was achieved to shorten the ventilation path for the diffusion of dirty gas, while improving the ventilation efficiency. A facile control system was specifically designed to consist of each control node in a modular approach. LoRa wireless communication was used to transmit data between control nodes. At the same time, fuzzy control was applied in the control system. Relative humidity and CO2 concentration were used as input variables, whereas, the speed control mode of main fans was used as an output variable. The quantization factors of input variables Kh and Kc were both 0.5, while, the quantization factor of output was 1. A general platform of MATLAB Simulink was selected to establish the model of the fuzzy control system. The simulation results showed that the proposed system responded quickly, while switched step by step in the four types of ventilation modes, including downtime, low, medium and high speed. A fence was applied as the ventilation unit to transform the fresh air, considering the air flow field after simulation. A field experiment was also carried out in a large-scale pig farm in Jianhua District, Qiqihar City, Heilongjiang Province of China in December 2019. It was found that the uneven coefficient of airflow was below 0.1 in the cement floor area of piglets, indicating a better uniformity of ventilation in the nursery piggery under the combined ventilation system of air supply and exhaust ducts. An infrared thermal imager and a gas detector were used to detect the environmental data of each area in the piggery. The measuring data showed that the temperature was kept between 21 ℃ and 25 ℃, the relative humidity was less than 70%, the concentration of NH3 was less than 5 mg/m3, the concentration of CO2 was less than 1 200 mg/m3, indicating the overall environment without other gases was suitable for the living of piglets. The combined ventilation system of air supply and exhaust ducts can be expected to realize the on-demand ventilation. Furthermore, the power consumption of the system was relatively low, ranging from 270 to 1 550 W. Consequently, the developed ventilation system can accurately control the piggery environment and efficiently alleviate the various changes between ventilation and heat preservation in winter.