Modeled construction and operating costs of different ventilation systems for lactating dairy cows.

The objectives were to compare capital costs of building and installation of 7 ventilation systems for adult lactating dairy cow housing and evaluate the energy use and operating cost between systems. A cost model comprising stochastic and parametric modules was created to estimate the number of fans operating each day based on temperature set points; annual profiles of daily maximum, minimum, and average temperatures; ramping functions to transition between seasons; and weather data from 7 locations in the United States. Costs were described as US$ per stall per year and operating costs as US$ (kW·h) per stall per year. Building costs amoritized over 10 yr ranged from $246 to $318, where a 16-row cross-ventilated design had the minimum cost and a hybrid design incorporating elements of tunnel and natural ventilation had the maximum cost. Lowering the summer temperature set point from 22.2 to 18.0°C to potentially improve heat abatement for high-producing cows increased cost by $10.10 (101.0 kW·h). On average, an exponential ramping function for transitioning between seasons cost $55.40 (554 kW·h) compared with $61.40 (614 kW·h) for a linear function. A tunnel barn ranged from $79.40 (794 kW·h) to $212.30 (2123 kW·h), and a natural design ranged from $32.60 (326 kW·h) to $81.80 (818 kW·h) in operating costs due to fan selection alone. Cross-ventilated barns benefitted from economies of scale and had similar operating costs as naturally ventilated barns in larger facilities. On average, mechanical systems cost twice as much to operate as natural systems, and operating costs in hotter US climates were approximately double those in milder climates. Selecting a fan with low energy efficiency can increase the operating cost of any ventilation system approximately 2-fold, making fan choice a critical design element.