Environmental characteristics of a swine gestation barn with an innovative cooling pad system

Abstract: Cooling and heating facilities are highly demanding in summer and winter, respectively, particularly for most large-scale pig farms in the typical continental monsoon climate zone in China. An energy-efficient ventilation system is essential to the environmental requirements for the growth and production of sow. Currently, a pad-fan evaporative cooling system is the most common method to control environmental temperature inside the housing for the large-scale pig unit. The operation of cooling process can provide comfortable temperature of fresh air, but make a big drop in the indoor temperature between both ends of a large pig house. However, the uneven distribution of fresh air in a large house can result in the extreme need for a high energy consumption in a cooling system. In the case of current pad cooling system, it is difficult to meet the requirements of thermal environment and air quality for pregnant sows in large-scale sow farms. Fortunately, a ground channel ventilation system is widely concerned in the environmental control field of pig farms, because it can cool down in summer and simultaneously warm up in winter. In the present study, an innovative ventilation system combining cooling pad and ground channel was proposed to explore the environmental characteristics inside a swine gestation barn. This feasible system was designed to significantly improve the uniformity of air distribution, while, reduce the energy consumption, by controlling the temperature difference between the front and rear of a large pig house. A typical pregnant sow house with this innovative ventilation system was built in Henan Province, China. The specific ventilation mode was as follows: the outdoor fresh air entered the underground duct system below the solid floor of the sow through the cooling pad, then flew into the house uniformly from the air inlet in front of the head of the sow, and finally the waste gas was discharged out of the house by the roof fan. The house with the size of L×W×H 98m×47m×4m contained 1344 pregnant sows, and 24 rows of gestation stalls. Half of the area with the size of 49m×44m was selected for the environmental test. The field test was carried out to investigate the effect of new cooling system on environmental characteristics inside the pregnant sow house. The parameters related to thermal environment and air quality were measured to analyze the environment change of the pigsty in summer and winter. Temperature/relative humidity (RH) sensors, anemometers, air quality monitors, and air particle counters were used to measure the temperature/RH, air speed, NH3/CO2 content, and PM2.5/PM10 distribution, respectively, during summer and winter. The effective environmental temperature was recorded, and the breathing rate were calculated, in order to evaluate sow stress status in summer and winter. The results show that during summer, the temperature of input air was reduced more than 25% with the innovative ventilation system, while, maintaining the air temperature at (27.1±1.0) oC, and the average cooling efficiency was ?84.4 kW. During winter, the air temperature was retained at (17.7±1.2) oC without extra heating, and the average heating efficiency was 121.6 kW. More than 87% of the heat exchanged at the first half (close to the air inlet) of the system. The temperature, RH, and air speed were distributed evenly, where the temperature fluctuation was less than 3.8 oC. The indexes of effective environmental temperature (EET) and respiratory rate of sow were verified that the tested sows were under a comfortable environmental state of fresh air during winter, and slightly heat stress status during summer. The contents of NH3, CO2, PM2.5 and PM10 were distributed evenly in the large house, less than those recommended national standards released by Chinese governmental agencies. The innovative pad ventilation cooling system can significantly decrease energy consumption of environmental control, while maintain excellent air quality inside the swine gestation barn. This proposed cooling system can contribute to the crucial environmental-friendly and economic implications on swine production.