Abstract:
Cattle are prone to cold stress in a facility cowshed during winter breeding in severe cold regions, due mainly to the low temperature, high humidity, and poor air quality. There are some symptoms, such as loss of weight, reduced immunity, high incidence of diseases, and limited growth and development. However, the conventional heat preservation of the facility cowshed can hinder the scale of the aquaculture, such as the large energy consumption, high risk, high cost of facilities, uneven heating, difficult operation and maintenance, as well as the contradiction between ventilation and heating. In this study, a solar concentrating soil heating system was proposed for the cattle bed of the facility's cowshed. Solar energy was adopted as the heat source, the air as the heat transfer medium, and the soil under the facility cowshed as the heat storage and supply carrier. The low-carbon, low-cost cost and convenient maintenance were obtained to introduce the structure of the heating facility cowshed. The heating performance in Hulunbuir was evaluated to calculate the heating temperature, temperature difference, and heat transfer efficiency of the whole system. The soil temperature data of the cattle bed were tested and collected in the continuous heating and non-heating periods of the system. Furthermore, a systematic investigation was then made on the multi-dimensional distribution of the soil temperature on the cattle bed along the vertical, horizontal, and the direction vertical to the heat exchange pipeline. The results indicate that there was a periodic variation in the heating temperature and temperature difference of the system in the effective heating period of 5 h per day, which reached 50.4 and 30.4 °C, respectively. In addition, the highest and average heat transfer efficiency of the heat exchange unit were 71.81 % and 56.10 %, respectively. When the system is continuously heated, the soil temperature at a depth of 0.7 m is stable at about 2.7 °C. There was a significant decrease in the soil temperature as the system stopped the heating. There was an increasing trend in the soil temperature at the different positions of the cattle bed during continuous heating. While there was an increase in the soil temperature, with an increase in the soil vertical depth. The average temperature of the soil at 0.7 m was 11.1, 9.2, and 5.8°C higher than that at 0.1, 0.3, and 0.5 m, respectively. In the horizontal direction parallel to the heat exchange pipe, the soil temperature and temperature increment at the high temperature end of the heat exchange pipeline were higher than those at the low temperature end. Among them, the soil temperature increment and temperature rising speed at the high- and the low-temperature end were 6.8 ℃, 0.6 ℃/d and 4.0 ℃, 0.4 ℃/d, respectively. In the direction of the vertical heat exchange pipeline, there was the highest value in the soil temperature increment and temperature rising speed above the heat exchange pipeline, which were 3.9 ℃ and 0.3 ℃/d higher than those of the soil at 0.8 m away from the heat exchange pipeline. The finding can also provide a strong reference for the green low-carbon heating of facility cowsheds in severe cold areas.