CFD simulations of supplemental cooling techniques in cross-ventilated dairy buildings and associated greenhouse gas emissions

Abstract

Dairy ventilation studies typically focus on reducing heat stress. Dairy buildings are often constructed with ventilation systems that exceed recommendations without prioritizing energy use. Given the rising production costs that dairy farmers face, it is becoming increasingly important to implement energy-saving technologies that can help reduce operating expenses. In this study, we tested whether ventilation rates of dairy buildings could be lowered when the existing cross-ventilation system was supplemented with a ground source heat pump for conductive or convective cooling. Computational fluid dynamics (CFD) models were validated by comparing measurements taken in a cross-ventilated building to the simulated data. It was found that the presence of baffles helped cool the barn, and the difference between the inlet and outlet barn temperatures was less than 2 °C (0.86 ± 0.08 °C at 0.5 m height), as recommended. However, there were still warm spots (T > 30 °C) within the stalls. When conductive cooling was implemented, the air velocity could be lowered from 1.03 ± 0.34 to 0.71 ± 0.29 m/s, resulting in reduced energy consumption and associated greenhouse gas emissions (14.7–25.5 %) while achieving the same temperature profile. With convective cooling, air velocity could be lowered to 0.69 ± 0.18 m/s, leading to a 17.0–27.7 % reduction in greenhouse gas emissions. Moreover, it decreased the average temperature at the 0.45–0.55 m (cow sitting height) from 29.3 ± 0.80 °C to 28.1 ± 0.15 °C. Given the projected rise in the social cost of carbon, supplementing cross ventilation with convective cooling has the potential to have economic and environmental benefits and lower the number of warm spots observed inside the building. However, a more detailed cost analysis is needed before making any recommendations.