Predicting the winter heat load of calf barns in cold regions under dual carbon context

Dairy production zone is often located in the cold regions, such as the northeastern provinces of China. Seasonal calving patterns are predominantly adopted in these cold regions. Calf production has concentrated in winter rather than summer, in order to reduce the negative impact of the heat on the mature cows' milk production. However, the calves can be subjected to severe cold stress during the colder months. The feeding practices during the calf stage can also dominate the adult milk production, thereby contributing 10%–20% of potential milk yield. Compared with the adult dairy cows, the calves exhibit the significantly lower environmental tolerance, due to the underdeveloped thermoregulatory capabilities. It is then required for the optimal architecture and environment of the calf barns. The prevailing low-temperature and high-humidity in winter barns can readily induce the calf diseases, such as diarrhea and respiratory infections, leading to the high morbidity and mortality rates. Alternatively, the retrofitting existing structures can be expected for the energy efficiency level. Before that, the heat load can be predicted to assess the heating energy demand, and standard energy savings rate. Among them, the thermal resistance and insulation performance of the envelope can significantly influence the effectiveness of the heating systems. Existing conventional calf barns generally exhibit inadequate thermal insulation in their envelope structures. Supplemental heating is also required to fully meet the environmental requirements for the calves in winter. It is very urgent to predict the heat load of the calf barns, in order to better understand the energy consumption under specific temperature and the minimum thermal resistance. Precise regulation can also reduce the carbon emissions in modern agriculture. This study aims to predict the winter heat load of the calf barns in the cold regions under dual carbon context. Case subjects were also selected as the representative cities in Northeast provinces of China. According to the energy-mass balance equation and heat exchange, a mathematical model was developed to predict the thermal loads in the cold-region calf barns. Thermal resistance of the building envelopes was firstly optimized to consider the latent heat production from the dairy cows, indoor heating thermal loads, heat loss through envelope structures and ground heat transfer, ventilation heat loss, and air infiltration heat loss. The minimum thermal resistance was recommended for the envelopes of the calf barns in different regions. Furthermore, a one-month validation trial of the thermal load model was conducted at a dairy farm in Ranghulu District, Daqing City, Heilongjiang Province, China, from January 24 to February 24, 2025. The temperature and humidity were then recorded both inside and outside the barn. The information parameters were then measured on the envelope structures of the calf barns. The results revealed that there was a high incidence of calf diarrhea and respiratory diseases in the experimental calf barn, with a mortality rate reaching 16%. Particularly, a large-scale pneumonia outbreak was observed in the barn in December 2025. Therefore, the environmental factors were the critical determinants of the calf health and production efficiency. The high accuracy of the prediction was achieved in a relative error of only 2.4% between theoretical heat load and actual heat dissipation. The minimum thermal resistance was recommended in the range from 0.81 to 1.91 m²·°C/W and 1.01 to 2.39 m²·°C/W, respectively, for the calf barn walls and roofs. There was the significant influence of the indoor humidity on the requirements of the minimum thermal resistance for the winter envelope structures in various cities. Once the relative humidity increased from 50% to 80% at the indoor temperatures of 12°C, the thermal resistance of the Harbin's calf barn south wall raised from 0.41 to 1.23 m²·°C/W—an increase exceeding 200%. Furthermore, the thermal load and carbon emission performance were compared across three building envelope scenarios (model barn, conventional barn, and enhanced barn). A 5,000-head dairy farm calf barn was selected in Harbin City, Heilongjiang Province, China. According to the minimum thermal resistance of the building envelope, the model of the calf barn was predicted to save 154,420 kWh of electricity per month, compared with the conventional barn. This value was translated to approximately 6,930 Yuan in electricity cost savings and a reduction of 8,480 kg of CO₂ emissions, indicating the significant potential to the energy conservation and carbon reduction. The social cost of carbon was incorporated with the economic and environmental benefits. The barn model was further enhanced the prediction, in terms of economic and sustainable environment. Overall, the minimum thermal resistance was determined for the winter heat load for the calf barns in Northeast China. The finding can provide the theoretical references to improve the calf rearing environments in the cold regions, in order to advance the energy conservation and emission reduction in calf barns.