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
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
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
- 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.