Trends in tunnel ventilation

By Sharon Thatcher –

As farm buildings grow in size, and livestock herds grow in numbers, so too are the concerns for proper ventilation. While natural ventilation is still common—especially in the beef industry—the poultry and swine industries use a lot of tunnel ventilation which uses large fans to generate air movement over the animals. That concept is also showing up in some dairy facilities.

tunnel ventilation

Tunnel ventilation systems are popular for poultry, swine and dairy barns. The fan banks shown here help to ventilate a large dairy operation in eastern Wisconsin.

Morgan Hayes, PhD, P.E., University of Kentucky, has worked in several areas of the Midwest and has seen the various trends. She noted: “People are more conscious of heat stress right now and concerned about it. As a result more people have moved from either natural ventilation or traditional sidewall ventilation to tunnel ventilation.

“The poultry industry traditionally uses a lot of tunnel ventilation,” Hayes continued. “The concept with tunnel ventilation is that you pull air in and you move it along the length of the barn with the most air speed that you can gain.”

Fans are located at one end of the barn and the air entry point at the opposite end. Air entry can be either through multiple basic openings or openings designed with evaporative cooling pads. This system is particularly used in the broiler industry and larger fans, in the 48- to 54-inch range, are the most desirable.

For the layer industry, sidewall or cross ventilation is popular. Fans are evenly distributed along the sides of the barn. Air enters through ceiling inlets and is drawn down through the space.

Hayes has seen the swine industry move from more natural ventilation in the Midwest to more mechanical ventilation in the past few years. Some producers are also commonly using 48- and 54-inch fans.


The dairy industry has been taking some steps toward tunnel ventilation systems but the larger dairy barns can require a lot of airflow and the desire for bigger and better fans is an ongoing goal for those facilities. Doug Overhults, PhD, P.E., also with the University of Kentucky, explained: “One of the attractions of the bigger fans is that you have fewer of them to maintain, and for the builder, it’s easier and less costly to put in fewer larger fans than more smaller fans…”

New trends

Tunnel ventilation systems have been around for a long time, but there are some interesting new trends.

Positive pressure ventilation (PPV) “In the swine industry, at least some of the farmers have started using a positive-pressure design for their barns,” said Hayes. “They build barns with filtration systems that push air into the barn rather than pull air out.”

Hayes noted that it requires a fairly large inlet area, “so they build large gables to handle all the filters, or offsets to the side of the barn to allow air into the barns. That’s a really unique and different design. It requires a little different construction because positive pressure means we need to focus on construction methods to keep moisture out of the walls.”

So far, Hayes has only seen the design used for the swine industry. “It’s gained popularity in the Midwest,” she noted. “I think the first barn we saw with this design was about a year-and-a-half ago, but a couple of farmers are using it, or at least testing the waters with their breeding herds, their more valuable animals. For some frame builders, long term, that could be a very interesting topic.”

Direct-drive fans. Another trend that Hayes has seen are direct-drive fans. “Traditionally we’ve had to put a variable speed control before the motor and they’re sort of inefficient when fans go below 100 percent [of operation speed],” she said.

Winter conditions are a case in point when fans are turned down. In those lower ranges, fans become more inefficient.

“And now they’ve come out with a direct-drive motor that’s able to reduce RPM on the fan and maintain or improve the energy efficiency of those fans. It’s an interesting concept for the industry as a whole,” she noted.

The new fans are more expensive, but Hayes believes they could become game changers for winter ventilation systems.

Ventilation basics

The objective of proper ventilation is always the same regardless of the animal, Overhults explained. “The general nature of ventilation is similar in that, in the wintertime, it’s all about removing moisture, ammonia and dust, just keeping the air fresh, supplying oxygen … In cold weather that’s usually a pretty low rate of ventilation,” he said.

“Then you progress to moderate weather when the rate goes up a little and you’re trying to maintain the target temperature in the building. And that target rate would be different for different animals and different growth stages. For poultry, for instance, smaller birds [with the exception of young chicks], you might be looking at temperatures inside that are 75 or 80 degrees; where for pigs you might be looking at 70 degrees or lower. And for dairy cattle the target temperature would be much lower, maybe 55-60 degrees. That makes your ventilation requirements a little different.

“Then you progress into summer, more hot weather conditions. Most all animals needs some cooling of some kind, and you can accomplish some of that just by exchanging the air in the building more rapidly. But air exchange alone usually is not sufficient to get the animals into their desired comfort zone.”

Evaporative cooling pads are a popular cooling system in some parts of the country for tunnel ventilation systems, particularly for poultry and swine. “The effectiveness really depends on what part of country you’re in,” Overhults said. “Where it’s really humid, they don’t work quite as well as they do in dryer climates.”

Evaporative cooling pads are part of the air inlet system located on the end opposite the fans. The incoming air passes through a cellulose pad about 6 inches thick. That pad is wetted and the air evaporates the water as it passes through the pad. The cooling effect can be from 10 to 20 degrees depending on weather conditions.


While most experienced builders make the correct decisions for helping to assure optimum results for tunnel ventilation, there are some common mistakes that are made.

“The most common error is when people are putting in a ventilation system and they don’t have enough openings in the inlet side. You’re looking for fairly large openings for the air to come through, because every time you choke it down, it makes the fan work harder,” Hayes said.

That can happen particularly when a barn is being retrofitted for a larger fan or when a second barn is built using the blueprint of the first. “[The builder] has cut bigger openings for the fans but they haven’t made a bigger opening for the inlet,” Hayes said. “If you are a builder and asked to frame out an additional fan, it would be good to ask if the farmer also wants additional inlet area.”

Another mistake Hayes has seen is fans that aren’t squared into their openings.

“Fans operate best if they go in square into a nice tight opening, properly built for the size of their shroud. So when those aren’t squared or not built right and someone has to jerk them into position and it torques the fan itself, it can change the efficiency on a fan. So make sure those openings are properly sized. It’s like putting in a window: it just doesn’t work well if it’s not a square opening.”

Overhults points to potential electrical problems. “It’s pretty important that they get their electrical system setup so they can operate all these fans. We’ve seen problems with some low voltage at the fans. Some of these barns can get really, really long and the wiring runs are very long. If the wiring is undersized, you can get some excessive voltage drops. I know many builders subcontract someone to do the electrical work, but they need to make sure that the electrician has his ducks in a row, because it does come up as an issue sometimes, and it’s pretty critical and hard to fix.”

Orientation is also important, especially for naturally-ventilated barns. “The best orientation sort of varies with location in different parts of the country. An east-west ridgeline works well in many places but you generally want to limit your exposure to wintertime prevailing winds and maximize your exposure to summertime prevailing winds. Avoiding any nearby airflow obstructions on the site is also important,” Overhults reminded.

Having two barns built too close together can change the wind dynamics. When building a second barn, know what changes may be needed to assure proper ventilation for both barns.

Still other issues arise when a new trend in caring for animals is introduced. An example is compost-bedded pack barns. Overhults has seen these in dairy operations in Kentucky.

A compost-bedded pack barn is an open barn where the cows are housed between milkings. They rest on top of a manure pack that is stirred with a rototiller or shank-type cultivator at least once or twice daily and topped with dry sawdust. “It’s stirred frequently to keep air in it, so it composts,” Overhults said. “It’s relatively dry because the heat generated from the composting action tends to drive off some of the moisture.”

Most compost-bedded pack barns have been built for use with natural ventilation systems and it is important to allow adequate space for the moisture to escape from those barns. Although the composting action tends to drive off some of the moisture, it is critical for the bedded pack not to become too wet Overhults noted. “Having an outlet for moisture in wintertime, a ridge vent, is something we’ve had to talk to people about a lot,” he said. “That’s a pretty important part of the building, to give an air outlet and take advantage of the fact that warm, moist air will rise and needs a place to exit the barn. RB


Related Posts: