By Dana Petersen
Note: Dana Petersen writes the Farm Energy column each month in Wallaces Farmer magazine. She is the coordinator for Iowa State University's Farm Energy program, in collaboration with the Iowa Energy Center.
Iowa State University Extension and Outreach will offer three swine ventilation workshops in northern Iowa beginning next week. These workshops will feature the expertise of Jay Harmon, Iowa State professor in ag and biosystems engineering. ISU Extension livestock specialists will also be on hand to present the latest information and to answer your questions.
The upcoming workshops are open to the public and will be held January 9 near Cresco, Iowa and January 13 and 14 at the Northwest ISU Research and Demonstration farm north of Cherokee, Iowa. Program topics will include management of ventilations systems, animal health and welfare, and energy use.
Workshops are free, open to farmers and others who are interested, and will be held January 9 at Cresco and January 13 and 14 at Cherokee
Previous participants reported that their knowledge of measuring air speed, velocity and humidity improved during the hands-on workshop activities. They also gained a better understanding of proper settings for inlets and adjustments to fan belt tension. One participant reported that, after attending a local workshop, he was able to reduce his annual energy expenses even though retail energy prices had increased.
Regarding energy consumption, Harmon notes that winter is an especially critical time of year for managing minimum ventilation to avoid costly heating bills in wean-to-finish buildings. Specifically, overventilating by as little as 10% can increase estimated annual LP consumption by 27%. Overventilating by 40% can double estimated annual LP consumption, Harmon explains.
"Wean-to-finish buildings present one of the greatest challenges to efficient winter heating," Harmon says. Facility management records show that a reasonable target for annual liquefied petroleum (LP) consumption is two gallons per pig space per year. However, actual consumption is directly affected by the time of year the weaned pigs are placed in the building. In addition, overventilation is more likely to occur during the wintertime.
Overventilation causes 80% to 90% of the heat loss from swine housing in winter
"Overventilation is responsible for 80% to 90% of heat loss in swine housing during the winter months," Harmon explains. "Unfortunately, overventilating is more common than expected because it's difficult to gauge exactly how much air is actually being exchanged by the ventilation system."~~~PAGE_BREAK_HERE~~~
In Harmon's example, a 1,000 head wean-to-finish building with newly placed pigs should be ventilated at 1500 cfm during the coldest weather. As pigs grow larger, this rate is adjusted. In order to meet the changing needs of the pigs and to minimize the total number of fans, a controller is used to slow fan speed and reduce air delivery. These are commonly known to as "variable speed" fans.
Variable speed fans should be used to fine-tune the ventilation rate especially during cold weather, Harmon explains. This optimizes a building's minimum ventilation and its overall energy efficiency.
Variable speed fans should be used to fine-tune the ventilation rate of hog buildings, especially during cold weather
When selecting variable speed fans, do not expect them to deliver less than half their rated airflow at 0.10 inches of water, Harmon says. From the example above, if 1500 cfm is needed, select a fan rated at 3000 cfm. This fan can then be used with a variable speed controller to deliver half its rated amount. An additional fan is needed to meet the air requirements when pigs grow larger than 75 pounds. In most cases, electricity costs to operate variable speed fans are less than heating costs for heated air forced out of the building due to overventilation.
There are limits to how much a fan can be slowed down using variable speed and still be effective. Fans operating at low speed cannot operate against much pressure. Fans facing prevailing winds should be protected with diverter cones or wind hoods. Also, fan motors receiving less than half voltage may become chronically overheated.
For more information about managing ventilation systems, download the fact sheets "Sizing minimum ventilation to save heating energy in swine housing" (PM 2089J) and "Managing swine ventilation controller settings to save energy" (PM 2089T) from ISU Farm Energy. You can also follow @ISU_Farm_Energy on Twitter for tips about energy efficiency all around the farm.