Large Ceiling Fans Offer Energy-Saving Way to Reduce Dairy Cow Heat Stress
If you're looking for ways to cool your dairy cows and improve their performance during next summer's heat, installing large ceiling fans in your free-stall barn is an option well worth considering. Although initial costs are higher than those of more traditional basket or panel fans, electrical savings should quickly make up the difference-especially as energy costs rise. You and your cows will also enjoy the quiet operation and pleasant breeze ceiling fans produce.
Summer heat stress lowers dairy cow feed intake and milk production. A year ago, I wrote about the proper installation of basket or panel fans- known as low volume, high speed (LVHS)-for summer cooling (see December 2002 issue). At that time producers were just becoming interested in large ceiling fans-known as high volume, low speed (HVLS)-that had started to appear in Ontario. Producers were asking these questions:
In the past year, research has been released that's starting to answer these questions. These studies describe airflow rates from HVLS fan installations, and compare them with LVHS fans in free-stall barns.
HVLS fans are similar to household ceiling fans but much larger. Blades range from four to 12 feet in length, making the fan eight to 24 feet in diameter. Powering these fans are 0.75 to 1.5-horsepower motors. They operate at speeds between 48 and 117 revolutions per minute (rpm), depending on diameter. Product literature states that a 20-foot-diameter fan can move up to 162,000 cubic feet of air per minute (cfm) at an average air speed of 440 to 790 feet per minute (fpm), or five to nine miles per hour (mph).
Originally developed for livestock barns, HVLS fans were first marketed for industrial applications to cool workers in large areas by increasing the air velocity around them. They were initially used for supplemental dairy barn cooling in the summer of 2000. Since then, their popularity's been increasing.
Supplemental ventilation with basket or panel fans usually consists of three-foot-diameter fans spaced 30 feet apart. These LVHS fans are most effective in free-stall barns when they're mounted over top of the freestall row and the feed alley to produce a jet of air over top of cows. They're designed to produce air speeds of 220 to 500 fpm, or two to five mph. In this type of installation, cooling takes place only in a narrow band in the fans' path.
HVLS fans, on the other hand, are mounted down the centre of the barn, usually over the drive-through feed alley (see Figure 1). They're typically spaced 50 to 60 feet apart and, as a rule of thumb, mounted one foot higher than the highest doorway to prevent interference with any equipment that can make it through the door. The fans move the air in the barn by first blowing it down until it hits the floor. The air is then directed horizontally and radially away from the fan's centreline.
In the summer of 2000, southern California dairy extension specialist Tom Schultz started comparing cows in barns with HVLS fans to those cooled with traditional LVHS fans. His team conducted three experiments over two summers to look at respiratory rates and milk production, as well as energy consumption.
In the second experiment, HVLS fans were compared to LVHS fans in a free-stall barn. The ratio used was one 20-foot-diameter HVLS fan to six three-foot-diameter LVHS fans on an equal area and cow population basis. There were a total of 17 HVLS fans and 100 LVHS fans. Each fan type serviced two free-stall groups on both sides of a central drive-through feed alley. One pen had cows bred by artificial insemination (AI) and one had cows with several breeding bulls. Each pen averaged 290 cows.
HVLS fans were hung over the centre of the drive-through feed alley and LVHS fans were mounted on top of the self-locking head gates. A sprinkler system was also used. All cows had the same feeding, milking and herd health management.
Milk yield and percentage of cows lying in the free stalls were compared for both groups. Regression analysis and correction for days in milk (DIM) showed identical milk yields of 90 pounds per cow per day at 150 DIM (see Figure 2) from cows with HVLS and LVHS fans. However, cows cooled with LVHS fans had a two-pound-per-day advantage at 75 DIM. Cows cooled with HVLS fans had a two pound-per-day advantage at 225 DIM.
The percentage of cows at the feed manger wasn't significantly different between pen or fan types. A higher percentage of cows cooled by HVLS fans were lying in the free stalls in both pen types in both the afternoon and evening compared with animals cooled by LVHS fans.
The total cost of the HVLS fans, including installation, was 30 per cent higher than for the LVHS fans. In terms of energy use, each of the 17 HVLS fans used 0.44 kilowatts (kW) per hour and each of the 100 LVHS fans used 0.54 kW per hour. In total, the HVLS fans used 86 per cent less energy than the LVHS fans.
The researchers conclude both types of fans were better than no fans at all. In some cases, cows produced more milk with LVHS fans and in others with the HVLS units. The HVLS fans used much less power.
Dave Kammel, a Wisconsin agricultural engineer, studied HVLS fan installations on five different farms including three-row, four-row and six-row free-stall barns. Air speeds were monitored using a digital anemometer in a grid pattern throughout the barns. He then mapped air speed profiles for each structure.
The horizontal velocity data from five interior fans in a four-row, head-to-head free-stall barn were studied in detail. The two end fans weren't used in the analysis because of the outside wind effect. In this barn, 20-foot-diameter fans were mounted at a 16-foot height and 60-foot spacing. Velocity data were averaged to develop a composite average air velocity pattern at five feet above the floor for a single fan (see Figure 3).
From this barn and the others studied, Kammel's team concluded that in most cases an air speed of over 100 fpm occurred over most of the barn. A velocity of 200 to 299 fpm was observed over the feed alley in a four or six-row barn layout. A velocity of 100 to 199 fpm was recorded over the interior row of free stall platforms for a four or six-row layout. A velocity of less than 100 fpm was measured at the outside row of free-stall platforms in a six-row barn.
Electricity meters were installed on two farms with HVLS fans to measure electrical use. The average energy use was measured at 14.5 kWh per fan per day or 0.604 kW of energy used per fan per hour.
Both the California and Wisconsin studies conclude HVLS fans reduced heat stress in dairy cattle. They also conclude that these fans used less energy than LVHS fans and were much quieter. An interesting anecdotal observation in Wisconsin was fewer birds in barns with HVLS fans.
Spacing HVLS fans 60 feet apart seems to work well for 20 or 24-foot diameter fans. The recommendation of mounting the fans one foot higher than the highest overhead door for safety considerations makes sense.
The major unanswered question is how long HVLS fans will last. They haven't been used long enough to have a maintenance history but, so far, no major problems have been observed.
Harold K. House is OMAF's dairy and beef structures and equipment engineer.
Schultz, T.A. and P. Williams 2002. Electric Power saving Fan Operation for Cow Cooling. 41st Annual Dairy Day, Animal Science Department, UC Davis http://cetulare.ucdavis.edu/files/31135.pdf
Kammel, D.W., M.E. Raabe, and J.J. Kappelman. 2003 Design of High Volume Low Speed Fan Supplemental Cooling system in Dairy Free Stall Barns. Fifth International Dairy Housing Conference Fort Worth, Texas.
This article appeared in the "The Ontario Milk Producer" magazine, December 2003.
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