Digital twinning of a novel cattle enclosure for control of methane emissions

GreenShed is a prototype circular agricultural system, where methane produced by cattle is removed and combusted, producing CO2 and energy, significantly reducing the global warming impact of cattle rearing. This approach requires a different type of cattle shed, with limited air leakage. Indoor conditions are controlled using heating, ventilation and air conditioning (HVAC) to maintain cattle comfort and wellbeing. The development of a GreenShed digital twin (DT) is described. The DT was used to size the HVAC system and assess overall energy performance, requiring empirically-derived models for cattle heat, moisture and contaminant emissions. Initial simulations indicated that the GreenShed concept was energy intensive, with a cooling/dehumidification requirement of up to 198 W/m2, and an energy use of 670 kWh/m2/yr. Efficiency improvements, including temperature-humidity-index-based climate control reduced primary energy use by almost 56%. A GreenShed prototype has been built at Easter Howgate Farm outside Edinburgh, Scotland. This has been extensively monitored. Contaminant data has been used to calibrate the infiltration characteristics of the model, indicating that the shed was subject to an average of 3.5 air changes per hour (ach), as opposed to the 1.2 ach, initially assumed. Re-simulation using the calibrated model showed that the environmental system, as originally sized, struggled to maintain the target indoor conditions. This issue illustrates that a lack of representative modelling data for an unusual application can have implications for its as-built performance.