|0608 PD: Ventilation fans for animal housing|
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A Focus on Energy Technical Data Sheet
Ventilation systems vary, depending on the barn configuration, climate zone and the type of animals being housed. For example, a naturally ventilated dairy freestall barn may require stirring fans only on the hottest summer days, while a tunnel-ventilated poultry barn will need the system to operate more regularly.
A ventilation system’s overall energy efficiency and its energy costs will depend on the fan. If you choose the least efficient fan available, you could double your energy costs and obtain less air output from the fan than more efficient models.
Energy efficient fans will reduce energy costs and offer better air output. However, after you choose the right fan, you must also make sure it is installed properly and maintained according to the manufacturer’s instructions. This [article] discusses ventilation fan designs, components, controls and maintenance. It also introduces different fan types and describes their use and ventilation benefits.
All fans are not created equal
Most fans are rated in two ways:
1. by air volume output in cubic feet per minute (cfm) at a specified static pressure (in inches)
Combining these two components provides a comprehensive rating for fan efficiency:
X cfm per watt at
For example, a low efficiency fan will have a rating of 17 cfm per watt at 0.05 inches static pressure and a high efficiency fan will have a rating of 20 cfm per watt (or greater) at 0.05 inches static pressure.
Fan components affect efficiency
As a fan’s diameter increases, its energy efficiency increases. Therefore, one large fan is more energy efficient than two small fans. From a ventilation control standpoint, it may be better to have multiple fans that can be staged; this configuration will help you achieve a balance between energy efficiency and efficient control.
In the past few years, several companies have introduced high efficiency single-phase motors that increase the motor efficiency to 77 to 84 percent and reduce energy use for the same air output by 11 to 26 percent. Contact your motor supplier for more information on high-efficiency single-phase motors.
If a barn is wired for three-phase electrical power, and fan motors are greater than one hp in size, you might want to consider three-phase motors. Premium efficiency three-phase motors offer higher efficiency (2 to 8 percent) than standard three-phase motors. However, three-phase motors – less than one hp in size – are not readily available.
Choose a thermostat that is designed for the appropriate environment and make sure the enclosure for the thermostat is rated for moist environments. Keep the thermostat and its enclosure free of dust. Dust will cover it, act as an unwanted insulator and yield an incorrect temperature reading. You should also calibrate thermostats once a year for critical applications to ensure they are working properly.
Wind-fighting fans: Choose the correct air flow ratio
Air flow ratio is defined as the air flow at 0.20 inches static pressure divided by the air flow at 0.05 inches static pressure. For 48-inch fans, air flow ratios range from 0.28 to 0.87 with an average of 0.74. There is little correlation between the ventilation efficiency rating and the air flow ratio; review both ratings when selecting a fan.
A safety requirement before you begin any fan or motor cleaning task, you must turn off the electricity to the fan and disconnect the unit from its power source. You should clean the accumulated dirt off the louvers and lubricate them with a dry lubricant such as graphite so they will not attract dust and dirt.
Dirt on motors can cause them to run hot, which leads to a breakdown in motor insulation and reduced motor life. A vacuum cleaner and a stiff brush will work best to clean motors, but for heavy deposits, a plastic scraper may be helpful. If the fan’s motor is totally enclosed and has a water-tight wire connection, you could use a power sprayer to clean the fan.
Loose belts can cause belt slippage, reduce air flow by up to 30 percent and shorten belt life. You should check and re-tension the belts monthly if the fan does not come equipped with an automatic tensioning device. This maintenance chore rarely gets performed as frequently as recommended by manufacturers. Therefore, most fan manufacturers offer V-belt self- tightening devices for new fans. Some of these devices can be retrofitted on existing fans to reduce maintenance costs and ventilation disruptions.
Finally, if your ventilation system is set up with emergency backup power or another ventilation system, test it regularly.
Summary of fan selection tips
• You should consider many parameters when determining the size and number of fans required for ventilation.
• Generally, larger diameter fans will be more efficient than smaller fans.
• Fans with a discharge cone will be more efficient than those without.
• Motor efficiency will affect energy use and the motor’s speed can affect efficiency and noise levels.
• Fan blade tip speeds greater than 4,500 feet per minute will create excessive noise levels. To keep noise levels low, fan revolutions per minute (rpm) should be less than 720, 480, 360 and 320 rpm for fan sizes of 24 inches, 36 inches, 48 inches and 54 inches, respectively.
• Machete or straight and teardrop blade designs are more efficient and accumulate less dust than cloverleaf-shaped fan blades.
• The clearance between the fan blade and the housing will affect efficiency and the static pressure at which the fan is capable of operating. Large clearances will allow air to leak back past the fan blade and housing. If the entrance of the housing to the blade is smooth and rounded, it will reduce the turbulence and drag of the air as it enters the fan blade air foil.
Fan types – stirring fans
Two types of stirring fans are used to ventilate animal barns:
• high speed fans
High speed fans
In a dairy freestall barn, high speed fans are typically installed over the feeding alley or over the center cow beds to provide cooling. Fans are generally spaced at a distance of ten feet for each foot of fan diameter. Therefore, 48-inch fans would be spaced at 40 feet, while 36-inch fans are typically spaced at 30 feet. Stirring fans are also commonly used in greenhouses and crop storage facilities to provide uniform temperatures and keep condensation from forming.
High-volume, low-speed (HVLS)
These fans are the most energy-efficient units available today. A 24-foot HVLS fan will move as much air as six high-speed fans and consume only 1/6 the energy. In a typical four- or six-row dairy freestall barn, the fans are placed over the feed alley every 35 to 60 feet, depending on the fan size. Current owners have described other advantages, including drier floors, less flies, fewer birds in the barn and reduced noise.
HVLS fans come with a variable speed controller to adjusts the fan speed. Some dairy farmers are using the fans at slower speeds to keep the air from stagnating during the cooler months.
Critics of this technology are concerned that the air velocity over the cows is too low to provide effective cooling if the fans are placed down the feed alley. Feed manger lockups, cows and stall dividers all impede the air movement from the center of the barn to the outside walls of the building.
Misting systems to augment ventilation
You should not mist dairy cattle in humid conditions, such as Wisconsin’s summer months, without using fans. If the water does not evaporate fast enough, wetting the cow can increase heat stress rather than decrease it. PD
For more ag-related energy efficiency information, visit: focusonenergy.com/agriculture
—From 2006 Professional Dairy Producers Annual Business Conference Proceedings