Never Too Early to Think Heat Abatement
Posted: February 28, 2017
It’s almost never too early to start thinking about hot weather. In Central Pennsylvania we hit 70 plus degrees during the last week of February, and it was a reminder that winter is coming to a close. As we begin to trade in our winter coats for sweatshirts and then sweatshirts for t-shirts, take some time to review your hot weather heat abatement plan for the coming summer.
The strategy for heat abatement remains the same, shade to protect animals from the solar heat load, high air exchange and air velocity to aid convective cooling, added drinking water for the animals, and finally added evaporative cooling. Although the basics of heat abatement are simple, I think a few points need to be discussed in more detail.
When circulation fans are hung over the feed area or resting area of an open, naturally ventilated shelter they should not be thought of as adding to or enhancing the air exchange of the shelter. In natural ventilation systems, the air exchange rate is driven by the size of the sidewall openings, the natural outside wind speed, and the building’s exposure to that wind. Circulation fans simply impart a velocity to the air already inside the building. In this application the fans are enhancing the air speed within the shelter, which will aid convective cooling, but they are not increasing the air exchange rate. With this in mind, the directional orientation of circulation fans may be less important than once thought. While it is still popular to orient fans to blow air parallel to the length of the barn in the same direction as the prevailing outside winds, this may not be as beneficial as once thought. Recently, anecdotal evidence would say that orienting circulation fans from two directions may decrease cow bunching during the heat of the day. For example, a freestall shelter oriented east to west may have the fans on the west half of the shelter orientated to blow air west to east, while fans on the east half of the shelter would blow air east to west. While this at first may seem that we are making fans ‘fight’ against one another—remember, they are just creating air speed within the shelter, not air exchange.
Another question I sometimes get about circulation fans is, “Which is more important, the air speed created or the volume of air moved by the fan?” Well, I would like to have both. Higher air speed creates more turbulence around the cow’s body and enhances convective cooling, while more air volume tends to increase the area covered and provides a larger volume of air to absorb heat and moisture from the cow. So I like to look for fans that provide a balance of high speed and high volume and not lean too far one way or the other. The type of housing may also be part of this discussion. If fans are being placed over two rows of head-to-head freestalls, there are more heat units (i.e. cows) per square foot than say a bedded pack, and cows standing in stalls will block the air movement for downstream cows.
When it comes to mechanical ventilation of dairy shelters, such as tunnel ventilation of a tie stall, the large exhaust fans in the end provide a high air exchange for the shelter. However, it has been observed that sometimes the air speed at and between cows is lower than desired. Several farms have seen increased performance of tunnel ventilation systems with the addition of circulation fans placed directly above the cow stalls in addition to the tunnel ventilation system. The circulation fans help boost the air speed around and between cows.
The final component of heat abatement is the addition of water for evaporative cooling. Before thinking of adding water, first make sure air exchange of the shelter has been maximized. If the added moisture is not removed from the shelter with air exchange, conditions within the shelter may become worse rather than better. The question is often whether to use soakers (direct evaporative cooling) or misters (indirect evaporative cooling). The answer really is they both work, but it depends on your housing system and goals. Indirect cooling lowers the ambient temperature of the air circulating within the shelter by raising the humidity. This cooler air is then used to enhance convective cooling of the animals. Direct evaporative cooling wets the skin of the animals and then, by this water evaporating from the skin, cools the animal directly. Direct evaporative cooling systems tend to use more total water and any water not directly put on a cow, but rather the floor, will add to the volume of material entering the manure system. Likewise, the ability of an indirect system to cool ambient air can be limited on humid days. The best evaporative cooling may be the use of both direct and indirect evaporative cooling together on the dairy. For example, use soakers in the holding area as cows wait to enter the parlor during milking, place indirect misters within the shelter for milder periods of heat stress, and add fence-line soakers for shorter periods of high heat stress. This may seem extreme, but with the use of good controls the whole system can be integrated and automated.
As we strive for maximum per cow performance and production, cow comfort needs to be maximized at all times of the year, and cows just aren’t naturally built for summer heat. So, it’s never too early to think about heat abatement. Get ready for summer heat before it gets here, because we know it is coming.