| In large-scale breeding pig houses,due to the high breeding density and poor control facilities,it will cause unsuitable temperature and humidity environments and harmful gases with excessive concentrations.High temperature and high humidity conditions in South China in summer are more likely to cause environmental imbalances in pig houses.Due to the weak resistance of sows and piglets and their high economic value,the environmental requirements of farrowing sow houses are higher than other types of pig houses.Aiming at this problem,this paper proposes a primary air return device,which is mainly composed of two parts: a fresh air unit and a return air unit.At the same time of cooling,a top-to-bottom airflow organization is formed,so that the harmful gas in the farrowing sow house flows into the manure tank through the slatted floor,so as to keep the environment in the pig house within a comfortable range.The primary return air control device was designed based on the facility conditions of a pig house in Zhanjiang City,Guangdong Province.The Fluent simulation software was used to simulate the concentration of harmful gases in temperature and humidity in the farrowing sow house,and the ventilation performance and thermal comfort in the pig house were tested.Evaluation,design the overall structure through simulation and calculation results,and carry out a control effect test of the return air control device in the farrowing sow barn.The main research contents of the primary return air control device are as follows:(1)Measure the actual data of the experimental farrowing sow barn in Zhanjiang City,Guangdong Province,establish an isometric three-dimensional model and set up various boundary conditions.In order to obtain the optimal supply air temperature and speed of the primary return air control device,simulation experiments were carried out on various environmental indicators in the pig house by means of Computational Fluid Dynamics(CFD).(2)Under the condition that the ventilation volume of the pig house is satisfied,the air supply speed is 0.5m/s.The simulation test was carried out with different supply air temperatures,and the analysis of the test results showed that the supply air temperature was 18°C to meet the requirements.Under these conditions,the temperature around the body surface of the sows in the pig house is 20.4°C～21.8°C,while the temperature around the body surface of the piglets is 21.8°C～24.2°C,and the relative humidity of the air around the non-pig body surface is 60.3%～63.5%.All meet the requirements of my country’s "Environmental parameters and environmental management of large-scale pig farms"(GB/T 17824.3-2008)for pig houses.Simulation experiments were carried out on the concentration of harmful gases in the pig house using different air supply speeds.The results showed that only the air speed was greater than or equal to 0.5m/s,and the concentrations of carbon dioxide,ammonia and hydrogen sulfide were within suitable environmental parameters.(3)In order to further evaluate the ventilation and thermal comfort in the farrowing sow house,the air age,PMV,PPD,and DR indices were used for evaluation.According to the human PMV,the pig body PMV is proposed,which can reflect the thermal comfort of the pig house to a certain extent.The air age value has a power-law relationship with the supply air velocity.When the air supply speed was 0.5m/s,the air age in the living area of piglets and sows was between 95 s and 230 s,indicating that the air quality in this area was relatively fresh.The PMV-PPD simulation results show that the PMV index of the living area is 0.63～0.75,the overall fluctuation is small,the thermal comfort of the living area is in a relatively comfortable range,and the PPD index value of the living area is 13.4～16.6,which is reasonable in the predicted unsatisfactory percentage.within the range.(4)The overall design of the primary return air control device was carried out.The model UCHA-60 TDC constant temperature and humidity fresh air fan was selected according to the ventilation volume and air dehumidification in summer,and the centrifugal return fan was selected according to the characteristics of long-distance air supply in the pig house.Through calculation,the diameter of the air supply pipe is280 mm,and the distance from the nozzle of the air supply pipe to the ground is 1.6m.A performance test of the return air control device was carried out,the data of various environmental parameters were measured every hour from 9:00 to 17:00 every day,and the change chart of each environmental parameter in the house with time was obtained.The results show that the daily fluctuations of temperature,humidity,carbon dioxide concentration,ammonia concentration,and hydrogen sulfide concentration are within the comfort requirements.Compared with the simulation,the carbon dioxide concentration is slightly higher than the simulation,but the overall environmental parameters meet the requirements. |
