Characteristics And Numerical Analysis Of Spatio-temporal Distribution Of Environmental Factors In Intensively Ventilated Swine Buildings

African swine fever has a great impact on China’s pig production capacity,stable production and adequate supply of pigs,together with promoting the transformation and upgrading of the breeding industry,is very important and urgent for current economic work of the Chinese government.In this paper,theoretical calculations were performed to develop an environmental heat transfer model for intensive swine buildings;to design a wireless sensor network(WSN)-based environmental monitoring system for swine buildings;to obtain information on the temporal and spatial distribution of environmental factors in centrally ventilated swine buildings;to develop a time series and multivariate model for predicting environmental parameters in swine buildings;to study the mathematical model and boundary conditions for numerical simulation of centrally ventilated swine buildings;and to apply CFD technology to carry out multivariate simulation test,and put forward indicators for the evaluation of the surface comfort of individual pigs,and summarize the optimal parameters for ventilation and cooling in the piggeries.The primary research work is as follows:(1)Research on environmental heat transfer model for intensive pig farmingBased on Fourier’s law of heat transfer and the theory of heat balance,considering the influence of heat convection,heat conduction,heat radiation and other heat transfer,to establish a multi-parameter steady-state heat transfer model that integrates the thermal and physical properties of the enclosure structure,physiological characteristics of pigs,operation management,fan control,wet curtain cooling,etc.,and to analyze the influence of different parameters on the effect of temperature control in pig housing by a parsing method.Based on the steady-state heat transfer model,a non-stationary heat transfer model of the dynamic change of environmental temperature in intensive piggeries was constructed,and the first-order linear non-uniform differential equation was solved using the commutative element method to obtain equations for the relationship between the instantaneous temperature of the piggery environment and parameters such as enclosure structure,operation management,wind speed,wet curtain,etc.,to establish the environmental heat transfer model of intensive piggery farming and provide a reference for the study of the spatio-temporal distribution patterns and numerical simulation analysis of piggeries.(2)Spatial and temporal distribution characteristics of environmental factors in centrally ventilated swine buildings based on WSNThe ZigBee meshed Topology structure was used for wireless distributed networking,nodes were using "one primary server multiple secondary nodes" to achieve multi-source multipoint The farming environment of the full range of monitoring,to achieve an integrated monitoring of the cultivation environment from multiple sources and points,and the WSN-based environmental monitoring system for pig housing was designed.Utilizing the environmental monitoring system of pig farm,central ventilation birthing shed and pregnancy shed temperature,relative humidity,ammonia concentration,carbon dioxide concentration,and other physical indicators were tested to obtain information on the spatial and temporal distribution of environmental factors in pig farm,and the environmental parameters of the birthing shed and pregnancy shed were summarized by comparing the environmental factors of the two central ventilation birthing shed with the longitudinal air supply type and vertical air supply type.The experimental results indicated that: the temperature and humidity variations in each area of the vertical air-fed delivery shed were negatively correlated,and the relative humidity was high;the variation of ammonia concentration and carbon dioxide concentration in the shed was highly significant(P<0.01);the system operated stably,the lithium battery could work continuously for 170 h,the average packet loss rate was 2.39%,the monitoring of environmental parameters was accurate and reliable,and the regional differences were significant.There were significant differences(P<0.05)in the temperatures between different time periods in the vertical air-fed birthing shed.Relative humidity and temperature showed a negative correlation with time,and the temperature field was more uniformly distributed than the humidity field.The peak point of the average temperature and humidity index level in the pig house was 75.30,and the probability of thermal stress in pigs was low.The results of the centralized ventilated pregnant sow barn demonstrated that the temperature difference between different time periods in the pregnant barn was extremely significant(P<0.01),the relative humidity showed negative correlation with the temperature change over time,the peak point of the average relative humidity in the sow breathing area of the barn was(85.85%),and the uniformity of the temperature field distribution was better than the humidity field(0.711<1.043).The mean temperature and humidity index in the barn was low(THI<75)and the pigs did not experience any thermal stress.(3)Prediction study of environmental parameters for pig farming based on time series and multivariate modelsFrom the point of view of mining the time series information of the historical environmental parameters of pig housing data,based on the time series model and multivariate model sequence,the temperature prediction model of a pig house was proposed.In terms of data pre-processing,error and missing values were filtered out for the temperature time series of pig house;a gate-based recurrent network was used to construct a temperature prediction model of pig barn.A multivariate model based on the gradient boosting decision tree was used to develop a temperature prediction model on missing value importance of pig houses.The prediction model was used in temperature prediction in the delivery sow barn and compared with the cyclic neural network model and inverse neural network in experiments.The comparison between the predicted and measured values revealed that the corresponding RMSE,MSE,and MAPE based on the GRU model were 0.25℃,0.19℃,and 0.65,and RMSE,MSE,and MAPE based on the XGBoost multivariate model were 1.21℃,0.71℃,and 2.50.In the temperature prediction model of the time series,the GRU model showed better prediction performance.The XGBoost model was superior in temperature prediction by multivariate model.A typical time series analysis model and a cyclic neural network model,based on a WSN-based environmental monitoring system,were used to develop a time series-based ammonia concentration prediction model for pregnant pig barns,and the results indicated that the two models with the best prediction accuracy were ARIMA and LSTM RNN,with ARIMA having the lowest RMSE of 2.27 and LSTM RNN having the smallest MAPE was 31.33%.A time series and multivariate model-based study on the prediction of environmental parameters of pig farming provides a model basis for the environmental warning and control of centrally ventilated swine buildings.(4)Numerical simulation and optimization of environmental flow field in concentrated ventilated pig breeding housesBased on the heat transfer model of the pig farming environment,using computational fluid dynamics techniques to establish the cultivating environmental models of centrally ventilated birthing houses and pregnancy houses,and conduct numerical simulation study of the ventilation cooling process.Multivariate simulation tests were carried out to study the effects of boundary conditions such as outlet location and ventilation wind speed on temperature and humidity changes and ventilation performance.The individual pig surface comfort evaluation indexes were proposed to summarize the better parameters of ventilation and cooling for the centralized ventilation pig house.The numerical simulation results of the temperature and humidity field of the trench duct inlet and central exhaust delivery shed indicated that the maximum difference between the simulated and measured values of temperature was no more than 4℃,and the average relative error was only 6.5%.The maximum difference between the simulated value and the measured value of relative humidity did not exceed 10% RH,with an average relative error of 7.3%.It could be seen from the spatial distribution of temperature and humidity that the temperature increased as the vertical height became greater,and the temperature gradient gradually enlarged;while the relative humidity decreased as the vertical height increased.The temperature field uniformity coefficient of the pig house was 1.29 and the relative humidity field uniformity coefficient was 1.51,the temperature field uniformity was better than the humidity field.The distance of the fan could affect the distribution of relative humidity in space,more far away from the fan,the greater the relative humidity changed,the more obviously it fluctuated.When the fan location was changed to the central part of the house,its temperature inhomogeneity coefficient was much lower,the temperature field throughout the whole building was more uniform,and the difference in comfort experienced by the pigs was much smaller.The numerical simulation results of the ceiling air intake,centrally exhausted pregnant shed showed that the maximum difference between the simulated and measured values of temperature did not exceed 1.54℃,and the average relative error was only3.06%.The maximum difference between the simulated value and the measured value of relative humidity did not exceed 10% RH,with an average relative error of 7.68%.As can be seen from the spatial distribution of temperature and humidity,the central location of the house presented as an airflow dead zone(not conducive to airflow diffusion),which had the characteristics of low speed,high temperature and low relative humidity.The uniformity of the pig housing temperature field was better than the humidity field.In the case of prioritizing the temperature field,the choice of the central air outlet unit would have the benefit of increasing the uniformity of the temperature field,but would simultaneously reduce the uniformity of the humidity field.Comprehensive consideration of temperature and humidity and their corresponding non-uniformity coefficients would lead to the selection of a ventilation speed of 0.5 m/s as the air inlet speed for the pregnancy shed.As the air inlet velocity increased,the uniformity of the temperature distribution on the body surface of pregnant sows would get progressively worse,while the uniformity of their relative humidity distribution would get better.The results obtained through the above work will provide reference for improving the efficiency of centrally ventilated swine buildings’ environment control,optimizing the ventilation mode,ensuring pig production operation,and providing help for the development of centrally ventilated swine building environment control equipment and intelligent facilities.