Ventilation facts

Proper ventilation improves energy efficiency and animal health

Poor ventilation can increase stress on your herd, decrease milk production and cost you thousands of dollars in lost revenue every year.

As you consider your ventilation options, WPS agricultural consultants can help you choose a cost-effective system to provide a constant source of fresh, clean air to keep your cows — and you — comfortable all year long. Proper ventilation also reduces moisture, disease organisms, manure gases, dust, as well as moisture and combustion products from unvented fuel-fired heaters.

It's especially important to consider upgrading your ventilation system if:

  • You notice a strong ammonia smell in the barn
  • There is excessive moisture condensation on walls or ceilings
  • Your herds have significant respiratory problems
  • Your buildings have dead air zones or areas with cool and warm spots

Use the ventilation systems calculator to estimate how much you could save on energy costs by using an energy-efficient ventilation systems.

There's more to fans than meets the eye

Fans are the driving force in ventilation, providing the all-important air exchange. You should select fans to provide winter, mild weather and summer ventilation rates based on the number of animals in the barn. Ventilation rates also vary by type and age of your animals, so it's important to check with the manufacturer to determine the appropriate rate for your operation.

At least four design factors influence the energy efficiency of a ventilation fan, including:

  • Motor efficiency - Some fan models with high-efficiency motors may use 20 percent less energy than other models. As the speed of a fan increases, turbulence (and noise) of the air moving through the fan increases and efficiency decreases. A fan or ventilation system does not need to be noisy to be effective.
  • Blade design or shape is also important for determining energy efficiency. Some blade designs reduce or minimize dirt buildup. Generally, a machete- or teardrop-shaped blade is more efficient than one shaped like a cloverleaf.
  • Blade-to-housing clearance is also important when choosing your fan. Fans with large clearances between the tip of the blades and the housing generally have low static pressure capabilities and low efficiencies due to the "blow-by" that occurs during the fan's operation.
  • Housing design also influences fan efficiency. The shape of the opening, particularly the point at which the air enters, determines how much air is lost.

Energy savings can add up quickly

According to a recent study by the University of Wisconsin-Madison, ventilation represents the largest electrical load on 30- and 60-cow dairy farms. Switching to energy-efficient fans can produce savings of 12-15 percent in both small and large, freestall barns. Most energy-saving technologies pay for themselves in two to three years, so it makes good economic sense to take a hard look at your ventilation system.

There are many things to consider when choosing new, energy-efficient ventilation systems for your buildings. Any exhaust-type mechanical ventilation system includes three components to work properly: fans, fresh air inlets and controls. Choosing the right ones can make a real difference for your animals, family and budget.

Rules to live by when purchasing and installing energy-efficient fans

Efficiency ratings are good ways to compare two or more fans, providing they meet your system performance requirements. While fan efficiency is an important consideration, you should also consider the following points when making purchase decisions:

  • Initial cost of fans, along with installation costs
  • Parts availability
  • Noise level
  • Housing durability
  • Ease of cleaning
  • Expected annual hours or operation
  • A larger-diameter fan is usually more efficient than a smaller one — larger blades move more air per unit of energy input
  • One large fan is usually more efficient than a number of small ones
  • When two fans have the same blade diameter, the one with the lower horsepower or motor current input rating (motor full load amps or FLA listed on the motor name plate) is usually more energy efficient
  • If two fans have the same airflow and static pressure capabilities, the one with the lower-speed motor is usually quieter and more energy efficient
  • Look for Air Movement and Control Association (AMCA) "Certified Rating" seals to assure you're getting the performance you're paying for
  • Choose locations for fans to prevent interference with movement of people, cows or feeding equipment. Protect all belts, blades, pulleys or other moving parts to be sure that people or animals do not become entangled
  • Locate fans above the alley where cows stand to eat. Aim the fans to blow air along the alley and at a point on the floor below the next fan in the series
  • Anchor fans securely in place to minimize vibration
  • Provide individual switches for each fan. Also, provide a properly sized fuse, circuit breaker or overload device for each fan that will turn off electricity to the fan if it becomes overloaded

Good ventilation requires proper air exchange and flow

Proper ventilation is necessary year-round to remove moisture and manure gases, as well as excess animal heat during warmer months. While many modern free-stall barns are designed to provide maximum cow comfort, many older facilities simply do not provide adequate ventilation. Whether you have a tie-stall or stanchion barn or a free-stall design, proper ventilation will help you provide a healthier and more productive environment for the cows and the people working in the building.

Different types of barns have different ventilation requirements. It's always a good idea to talk with your WPS Agricultural Consultant to investigate the most cost-effective ventilation system for your operation. If you're contemplating making some changes in your system, here are a few things to consider.

Free-stall barns are usually located on high ground with no obstructions to wind, and the wind blows through large sidewall openings. This air exchange carries hot air and moisture away from the animals. In summer, it may be necessary to deliver air at high velocity to the animals, which is usually done by strategically placed, large-diameter fans. To get maximum benefit, they must be located where heat stress is likely to cause the most impact to the animals. Typically the fans should be placed along the alley at 30-foot intervals if they're smaller than 36 inches in diameter and at 40-foot intervals if greater than 36 inches in diameter. Aim the fans to blow air along the alley and at a point on the floor below the next fan in a series.

Tunnel ventilation is a special summer ventilation system that provides a combination of the high-air-exchange rates and high-speed airflow over cows in tie-stall or stanchion barns. To equip a barn for tunnel ventilation, place large exhaust fans along one end wall of the barn, and place large openings along the other end. Close all windows, doors or other openings along the sidewalls. The fans will pull fresh outside air through the inlet openings across the cows, exhausting hot air out the fans. Tunnel ventilation designs are based on the cross-sectional area of the barn and air velocity. The minimum air velocity recommended inside the barn should be 2.5-3.5 mph, with the inlet sized at 2.5 ft2 per 1000 cfm of fan capacity to provide proper inlet velocity.

If you're using a tunnel ventilation system, be sure to have a plan for providing emergency ventilation if there is a power failure. It's also important to note that tunnel ventilation is not a cold weather ventilation system. An alternative ventilation system using sidewall fans and slot inlets is recommended for winter in tie-stall or stanchion barns.

Whichever ventilation system you have, be sure to select good quality, high-efficiency fans. Your WPS Agricultural Consultant can help you choose the best option for your operation.

Don't forget the controls

Thermostats that control fan operation are critical to energy-efficient ventilation systems. In older buildings that lack proper insulation, a normally closed safety thermostat may be installed for winter fans. The safety thermostat is set at 33-34°F so the fan will turn off if the barn temperature falls to that level. Mild rate fans should be controlled by a thermostat to turn on at 40-45°F. Maintaining the barn at about 40°F will help control condensation in older barns.

Manual controls are often used for summer systems. You may achieve greater energy savings by operating summer fans with a thermostat set at 60°F. During cool summer evenings, the ventilation rate will be reduced automatically to the mild rate.

One caution: barns that have large cracks around walls or doors or large leaks will not benefit as much from the addition of air inlets as a relatively tight barn. Leaks in the barn should be corrected to attain the desired level of air mixing and distribution.

For more information

To learn more about which ventilation system can help you reduce energy costs and improve your herd's health and comfort, contact a WPS agricultural consultant.