Barn Ammonia: A Natural-Ventilation Bound for Dairy Housing

Ammonia released from manure and soiled floors in dairy barns irritates the airways of cattle, and chronically elevated concentrations are associated with respiratory disease and reduced milk yield. This paper models a stated herd of 100 cows in a cubicle barn of 1,800 m2 floor area and 9,900 m3 air volume, with a temperature-dependent emission factor, and derives the ventilation rate required to hold the indoor concentration at or below 10 ppm. In winter (slurry at 7.0 C) emission is 13.93 g per cow per day and the required rate is 2.18 m3/s (78.6 m3/h per cow). In summer (slurry at 24.0 C) emission rises to 29.93 g per cow per day and the required rate is 5.06 m3/s. Sizing ridge and eave openings to deliver the winter rate at a wind speed of 1.0 m/s with an 8.0 K stack difference requires an effective opening area of 2.46 m2 (ridge outlet 2.75 m2, a 4.6 cm slot; eave inlets 5.49 m2). On a calm mild winter day the same openings deliver only 0.96 m3/s and the concentration reaches 22.6 ppm; near-isothermal calm air gives 32.0 ppm and half-closed openings 45.2 ppm. Holding 10 ppm on the calm mild day by stocking alone would require 43 cows. The winter rate removes heat at 22.3 kW under design conditions and 55.7 kW in a cold snap. Natural ventilation meets the threshold only when wind or stack effect is present; calm conditions require mechanical assistance or reduced stocking. SIMULATED, NOT MEASURED. AI use disclosure: This paper was prepared with the assistance of Dave, an AI system built and operated by Aldred Industries. Dave wrote the simulation code, performed the calculations, and drafted the text under the direction of the named author, who is responsible for the paper's content. No measurements were taken.