June 29, 2020
John Tyson - Penn State University
When trying to address heat abatement in a dairy there is always a budget. Sometimes that budget is financial, meaning only X amount of dollars can be spent to buy Y amount of resources. Other times it is an electric budget, meaning there is only so many Amps available to power fans. Still other times the water available for sprinklers, soakers, or misters is limited. With all these budgets in mind we need to prioritize where and what kind of heat abatement will do the most good with the resources available.
Start with the basics. Shade, Air Exchange, Air Velocity, and Water. Providing shade to lower the radiant heat load the animals receive is the first step in heat abatement. In confined housing this is the role of the shelter roof, if animals are on pasture consider simple shade structures to allow the animals relief from the sun during the heat of the day. Air exchange is fresh air in and stale air out. In most of the Northeast and Midwest this is done with natural ventilation. The two largest factors driving natural ventilation are natural airspeed and the size of the wall openings. As designers and managers, we can influence the size of the opening. The side and end walls should be as open as possible to utilize as much of the natural airspeed as possible. Welded wire panels and bird screen with large openings will leave more effective opening then shade cloth or dimensional lumber. Open walls at cow level to allow air in at the lowest level. If natural ventilation cannot be achieved than look toward mechanical ventilation. Either with a negative pressure system where air in drawn out of the shelter, producing a negative pressure within the shelter that draws in the fresher outside air. Or a positive pressure system where fans push fresher outside air into the shelter, producing a positive pressure within the shelter. The goal here is to exchange the air within the shelter about once per minute.
Once air exchange has been achieved than look to increase air speed at animal level. Increasing the air speed at the animal will increase the convective cooling of the animals. The goal here is to be in the 5 mph or 450 feet per minute range. However, remember that large circulation fans only create air speed within the shelter and do not add air exchange. Hot stale air moving at high speed is not heat abatement. You need to exchange the air within the barn to get heat abatement.
Lastly after achieving air exchange and air speed, water can be added to the mix with either soakers or misters to aid in evaporative cooling. In the more humid Northeast, feed line soakers that add water directly to the cow have shown to be more effective but do use more water than misting systems. So, if water availability is an issue adding misting nozzles directly in front of circulation fans where it can be evaporated into the air, and therefore lower the ambient temperature may be an option. However, both systems depend on evaporating the water into the surrounding air and therefore raise the humidity level within the shelter. Again, having good air exchange to remove this extra moisture from the shelter in a must.
When due either to finical budget or amperage budget the question often is where to locate circulation fans within a shelter. In my opinion I tend to focus over the stall area and particularly head to head stalls. The goal is having cows rest for 12 to 14 hours per day, and the head to head stalls concentrate the cows in that area. Providing high air speed in this concentrated area I feel gives you good use of limited resources.
Another area to concentrate heat abatement resources is the parlor holding area. Once again animals are concentrated in one area two, three, or more times per day and this space can heat up very quickly. Maximizing air exchange to remove this extra heat and adding additional air speed, and evaporative cooling can help limit the increase in body temperature while in the holding area.
All projects have a budget of one form or another. Good planning and understanding the basics of heat abatement will help get the best return for limited resources.