Evaluating the indoor environment quality of pig house with hybrid ventilation system in the severe cold region

A ventilation system can often dominate a controllable environment in a pig house. A vertical ventilation system with roof and manure pit exhaust fans has been introduced into some newly built pig houses in Northern China, in order to improve the microclimate environment. However, it is still unclear on the adaptability of this ventilation system in cold seasons. This study aims to evaluate the suitability of the ventilation system in northern China. A field measurement was also performed in the newly built pig house using the vertical ventilation pattern in Inner Mongolia. The pig house was equipped with air inlets on the sidewalls, while there was no ceiling inside. Two independent units (U1 and U3) of the pig house were selected for the experiment. Portable monitoring unit (PMU) and particulate concentration monitoring unit (PCMU), internet of things (IoT)-based environmental monitoring devices, were developed to continuously measure indoor temperature, relative humidity, carbon dioxide (CO₂), ammonia (NH₃) and total suspended particulate matter (TSP) concentrations in autumn and winter. Ventilation rate was also recorded with the feed intake, feed conversion ratio, mortality, initial and final average weight of the pigs. Then, the adaptability of the vertical ventilation was evaluated in the extremely cold climate using the indoor thermal, air quality and spatial uniformity of the pig house with production performance. Results show that the average temperature and relative humidity during measurement were 22.7 ℃ and 59.6% in the ranges of 18.2-29.2 ℃ and 38.6%-82.1%, respectively. Meanwhile, the average ventilation rate fluctuated at 0.34-0.39 m³/(h∙kg). Seasonal means of NH₃, CO₂ and TSP concentrations were 6.5 mg/m³, 2200 mg/m³ and 2915 μg/m³, which were fluctuated in 3.1-12.3 mg/m³, 1244-3 400 mg/m³, 1563-4215 μg/m³, respectively. The thermal and air quality environment of the pig house was generally controlled in a suitable state for pigs. While effective environmental temperature was 27.1-30.7 ℃ in the pig house during the nursery period, indicating mild heat stress to the pigs with a duration of 12.9% of the measurement. The Non-uniformity Coefficient of temperature, relative humidity, and NH₃, CO₂, and TSP concentrations in the pig house were 0.01, 0.15, 0.45, 0.03, and 0.15, respectively. Meanwhile, the maximum differences in the temperature, relative humidity, and NH₃, CO₂, and TSP concentrations in the indoor space were 1.5 ℃, 32.8%, 4.8 mg/m³, 445 mg/m³, and 1296 μg/m³, respectively, indicating the relatively uniform distribution in the environment. Average ventilation rates of U1 and U3 units in the nursery period were 0.35 and 0.39 m³/(h∙kg), respectively, which were 0.34 and 0.35 m³/(h∙kg) during the fattening period. Generally, the ventilation of the pig house fully met the minimum demands in northern China in cold seasons. Moreover, the concentrations of NH₃ and CO₂ in pig houses were 50% and 52% lower than those without manure pit fans in Europe. There were also comparable daily weight gain (842 vs. 818 g/d), feed conversion ratio (2.68 vs. 2.79), and mortality rate (1.68% vs. 1.31%) of the pigs in the U1 and U3 test units. The thermal environment and air quality of the experimental pig house were suitable for the production performance of the pigs. In conclusion, the tested pig house was equipped with roof and manure pit exhaust fans but without ceiling settings, where the thermal and air quality environment was maintained in a suitable state in autumn and winter. Generally, the production performance of pigs was also achieved under such an environment.