Ventilation and heat preservation effects of heat recovery ventilation system in calf shed

Livestock production significantly depends on the animal health and comfort. In animal housing, the environmental atmosphere and temperature usually play an important role in livestock productivity. To remove moisture and odors replacing with fresh air has become necessary to promote the air quality for confined animals. However, this ventilation can pose a negative impact on the health of calves, particularly in the cold environment in winter. Therefore, the reasonable ventilation is important to balance the impact of cold environment and air quality on the health and productivity of calves in cold regions. In this study, taking the Xinjiang province, China, as research regions, a heat recovery ventilation system was investigated in 2019 and 2020, in order to reduce the impact of cold stress on the calf health, and further to achieve good performance of energy conservation and emission reduction in barn. There were a heat recovery cavity and a fiber air supply duct in the heat recovery and ventilation system. The heat recovery cavity was a cuboid with the dimensions of 34 m×1 m×0.4 m, including 10 fresh air ducts with the diameter of 150mm. The end of the cavity was connected with a fiber supply duct with a length of 70 m, where the diameter of the fiber duct was reduced from 350 to 300 mm. There were two rows of small holes with the diameters of 8 and 11 mm at the bottom of the fiber duct, where the spacing between holes was 50mm. Two cattle barns with the same structure and size were selected as the test barn and the control barn, respectively. The building size of both barns was 100 m×12 m×3 m. There were 112 Simmental cattle weighted around 50 kg in each barn. Two sets of heat exchange ventilation systems were used in the test barn. The equipment was suspended at a height of 3 m from the ground. The cold air outside the house was fed into the heat exchange chamber through an air supply fan with a positive pressure. After heat recovery, the fresh air inside the house was uniformly fed into the chamber through a small hole in the air supply pipe. Concurrently, the hot air inside the house was entered into the chamber through an air return fan under a positive pressure, transferring heat to fresh air, and then away from the chamber. As such, the control barn was naturally ventilated. The environmental data of two houses measured, while, the equipment performance of the heat recovery ventilation system was evaluated during the field test. Based on the experimental data, the performance of equipment was optimized further to improve the air quality in the shed. The results showed that the heat recovery ventilation system increased the temperature of fresh air by 10.15 ℃, and significantly reduced the concentration of daily CO2 and NH3 by 173.15 and 0.63 mg/m3, respectively. Both systems can provide the ventilation amount of 1 097.83 m3/h for the test barn. The fan efficiency can reach about 55%, within the normal range. Specifically, the average wind speed at the outlet of air supply duct was 2.45 m/s, whereas, the wind speed at the beginning and end of air duct were 2.76 and 2.34 m/s, respectively. The system indicated a good energy saving, with a heat recovery efficiency of 76.17%, and an energy efficiency ratio of 3.1. The heat recovery efficiency was within the normal range of 50%-80%, whereas, the energy efficiency ratio was higher than the minimum energy saving standard of 2.5. The findings demonstrated that the proposed system can ensure an improved environment in the barn, with a high efficiency of energy recovery. This system can be used to balance between the ventilation and heat preservation during the calf production in winter. The reasonable trade-off between energy saving and environmental protection can be offer a great significant guidance for the calf production.