Making Informed Ventilation Choices

 By Bruce Derksen for American Dairymen Magazine

 The ideal ambient temperature for a dairy cow is between 32F/0C and 68F/20C, but when the thermometer rises above or falls below these levels, cows begin to divert their energy from milk production to heating or cooling, causing a potential ten percent or more decrease in milk yield.  Heat stress during late gestation is also shown to reduce calf birth weights and lower subsequent milk production.  To combat these challenges and help them reach their goals, cows need a constant source of fresh, clean air.  Ventilation systems are an essential component to deliver this relief and help maintain optimum performance in confined feeding operations.

“The critical elements of design are fast moving air in the resting space, sufficient air changes per hour and a system that works in the winter, as well as in the summer,” said Dr. Nigel Cook, University of Wisconsin Madison dairy facility ventilation expert, during a recent “Mechanical Ventilation Options for Dairy Barns” seminar.
The goal of ventilation is to reduce moisture and humidity produced by the animals through respiration, water spillage, manure and urine in colder weather and control the heat created in hot weather.  At its potential, a proper ventilation system should remove and discharge air contaminants, odors, gases, dust, CO2 and pathogens, plus provide adequate quantity and qualities of evenly distributed fresh air.
When making decisions, take location and yearly climate ranges in both humidity and temperature into account.  Consider how a cold, moderate or warm environment barn will work for your operation.  Insulation is an option in all climates as it will improve ventilation and reduce the flow of radiant heat in the summer and curb sweating and accumulation of condensation on cold surfaces in winter.
Two basic stages of air systems are involved in the ventilation of dairy barns.  First, the exchange of air throughout the space and second, the directed airflow or airspeed onto the cows.
To control and discharge contaminants, odors and pathogens, some operations use natural ventilation systems making use of open sides or curtain walls that can be manipulated to allow the entry of fresh air.  This system can be slower to deliver adequate air turnover and depends largely on exterior air movements to work properly.
More efficient exchanges are achieved through mechanical or power ventilations making use of a combination of inlets and fans that control the amount of air moving in and out of the barn.  Through automation, a more consistent delivery of fresh, clean air can be provided in all temperature ranges and climates.
A popular example of this type of system is tunnel ventilation air exchanges employing large fans of 4- 6 feet in diameter, drawing air from one end of the barn and moving it at a speed fast enough to provide convective cooling before exhausting it out the other end of the barn.  These systems are highly automated and can be programmed to provide the required air exchanges per hour.  They are easily placed and oriented as desired, controlling fly concerns and excessive bunching of cattle.
When proper air rotations have been maintained, airspeed or airflow systems should be added to enhance cooling of the animals.  Fans should be installed wherever cows are located and over the stall rows.  For major cooling needs, the higher the airspeed the better, with fans now available to provide anywhere from 15 to 36 mph off the face.  Newer models allow almost infinite adjustability through newly designed controllers, thermostats, variable frequency drives (VFD) motors and electronic commutative (EC) variable speed motors.
Keep in mind that all mechanical or power ventilation systems consume energy.  It is imperative to use proper designs, sizing, and control selections, plus keep maintenance current.  Some newer designs claim to lower energy costs by as much as fifty percent in the right situation.  
The construction of a dairy barn is a huge investment, but without proper ventilation and cooling, it can be wasted if cows are losing production from cold or heat stress.  Choosing the right system for the operation, whether naturally occurring or mechanically driven, and automating it to its full potential through the use of energy reducing monitors and controllers, will ultimately result in a more ideal environment for cow comfort and production.