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Straight Talk About Hog Barn Ventilation Screw-Ups

In the last 12 months, the Mankato, MN-based specialist says he has spent a great deal of his consultancy time on what he describes as the screw-ups that happen with ventilation. In a presentation to an audience made up largely of veterinarians and consultants attending the Leman Swine Conference in mid-September, Brumm offered this list of ventilation challenges that he commonly comes across: Understanding

In the last 12 months, the Mankato, MN-based specialist says he has spent a great deal of his consultancy time on what he describes as the “screw-ups that happen with ventilation.”

In a presentation to an audience made up largely of veterinarians and consultants attending the Leman Swine Conference in mid-September, Brumm offered this list of ventilation challenges that he commonly comes across:

  1. Understanding ventilation controllers

    This challenge rises to the top of Brumm's list. All controllers are designed to do the same thing — operate the components of a ventilation system. But with differing brands of equipment and controllers often combined in a “system,” complications arise. Add to that a producer or contract grower who doesn't understand their controller or who may have had his hands slapped by the production supervisor who says: “Don't touch the damn thing.”

    “The net consequence is the pigs suffer,” Brumm emphasizes.

    “There is a whole litany of issues associated with controllers, but the number one issue is that once the controller is set at 78°F, many think the temperature in the room ought to be 78°F all of the time. Remember, the set point is the decision point of the controller — and it may be a lot warmer or a lot colder than that, depending on how you told the controller to make decisions,” he begins.

    “Almost every barn built in the last 10 years in the Midwest has variable-speed fans, and I will guarantee that few understand them,” he says.

    To make his point, he offers this multiple choice question: “When you set the stage 1 minimum speed at 50% on the controller, is it:

    1. 50% of the fan output?
    2. 50% of the fan speed?
    3. 50% of the voltage coming into the controller?
    4. A funky number?

    “The correct answer is “d” — a funky number,” Brumm says. “First, you must start with an understanding of variable-speed fans,” which he says requires an understanding of these variable-speed fan rules:

    Rule #1. “In variable-speed fans, 50% of the rpm (revolutions per minute) is never 50% cfm (cubic feet per minute). A fan blade must rotate at some minimum speed to start creation of static pressure,” he continues. “Every increase in rpm beyond this minimum is an increase in cfm. My basic rule is 65% rpm is 50% cfm.”

    Rule #2. “Voltage does not equal speed (rpm) or cfm. If a barn is wired for 230 volts and the controller sends a voltage signal of 115 v. to the fan, the fan may or may not respond with 50% rpm or 50% cfm. The reason is — every motor reacts to voltage differently.

    “If you put three different brands of motors on the same fan, you are apt to get three different fan speeds. That's why when you replace a motor you have to do like-kind-to-like kind replacement to maintain parity response on the fans.”

    The other confounding factor is that controllers do not have a feedback loop. “We simply have line 1 and line 2 and a neutral line going to the fan in 230 v. systems. The controller doesn't know what's connected, so it's up to the producer to adjust the controller for what's downstream (fan motor response to voltage). The controller just knows to send a voltage signal,” he surmises.

  2. Setting minimum fan speed

    Nearly all controllers regulate fan speed through a potentiometer that sends voltage in response to the controller decision.

    “Everyone sets minimum speed by dialing down the motor until it growls, and then they turn it up just a little bit,” Brumm explains. “The minimum speed should be 50% of the rpm. When the controller is set correctly for the fans in that stage, this is often 40% minimum speed, which will give you 50% rpm in most (popular) controllers. The reason is that all fan motors are totally enclosed air over (TEAO) and they require a minimum amount of air movement over the motor for cooling.

    “We know wind affects variable-speed fans and we do all kinds of funny things to compensate for it, but if we don't get the controller right, this one becomes a big issue,” he warns.

    Brumm says there is a general lack of understanding about how variable-speed fans respond to static pressure. Using a 24-in., Aerotech Model AT24ZCP fan, commonly installed as a pit fan in a wean-to-finish barn as an example, Figure 1 shows the results of Bess Laboratory testing at the University of Illinois agricultural engineering department. (; companies pay to have their fans tested and the site lists their performance).

    Figure 1 shows the performance of the fan at different static pressures and voltages. “The BLUE line shows the performance at 160 v., which is 70% of the voltage (230 v.), but at 0.05 static pressure, it gives my targeted 50% cfm,” Brumm explains. “If I go down to 140 v. (ORANGE line), which is still 60% of the voltage (capacity), I'm down to 9% cfm.

    “This is the relationship between voltage, static pressure and cfm. The interesting thing is if static pressure goes up to 0.10, say the wind is blowing into the fan or a ceiling inlet is restricted, even though I don't change my controller, my output declines to 20%.

    “Any time you have a facility with two fans for stage 1 and the expected output of the variable-speed fans is less than 50% of the cfm, unplug one of the fans and run the remaining one faster,” he advises. “That's just about an absolute rule.”

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  • Figure 2 shows the response of three commonly installed, variable-speed fans to voltage. In this example, the 12-in. fan (APP12), an 18-in. fan (AT18Z) and a 24-in. fan (APP24F) are all wired to 230 v. and the output is expressed as a percentage of the rated cfm at 0.05 static pressure. The goal is to get 50% out of that fan.

    As the graph shows, the 12-in fan requires 107 v., the 18-in fan needs 132 v. and the 24-in. fan requires 142 v. to reach the 50% goal. They are all often controlled by the same brand of controller and they are all downstream — wired with line 1, line 2 and neutral, he emphasizes. Therefore, controllers must be customized for the fan(s) that are installed in the variable-speed stage(s).

    “So how does the controller know what's there?” Brumm asks, and answers. “Many controllers have user-selectable motor curves that allow the controller voltage signals to fans to be tailored to specific fans,” he says. The number of user-selectable motor curves range from three up to 10 for different brands of controllers.

    “Failure to use the correct curve or correction factor is a common reason why variable-speed fans do not perform as expected,” Brumm notes. “When I set the controller at 50%, the voltage sent is a function of the motor curve selected. As an example, in one model of controller, if I select motor curve 9, when I set the controller at 50%, I am sending 111 v. When I set the controller to motor curve 4, at 50% minimum speed, the output is 146 v. That's why 50% is a ‘funky’ number,” he explains.

    Several controller manufacturers make guide sheets available with recommendations on the correct motor curve for various fans and/or fan motors.

  • Staging of fans

    “Just because it's originally wired one way doesn't mean it's right,” Brumm declares. As an example, he cites a wean-to-finish unit with five, 24-in. fans set on stage 1, plus a 36-in. fan set at stage 2. “When you do the math, stage 1 was ramped up to 26 cfm/pig (single stocked) and their idea on ventilation was to turn the controller down to 10%, thinking they would get 10% of the cfm or 2.6 cfm/pig. You can imagine the mess in the hog barns,” he declares. His solution: Start unplugging fans on stage 1 until you can accomplish the desired minimum ventilation at 50% of the fans rated cfm. In this situation, rewiring of the 24-in. fans for multiple stages was required.

  • Conserving heat

    A year ago, producers were paying up to $2.20/gal. for pre-booked liquid propane (LP) and it was going higher. In mid-September this year, tanker loads of LP were being priced on either side of $1.00/gal.

    “Fuel cost has come down — but it's still a cost. It's a major cost to contract growers because it comes out of their pockets,” he reminds. “Getting ventilation right when you start the pigs is huge in terms of gallons of propane — more so than anything you can do with insulation. You've got to keep the heat in the building.”

    As pigs grow, they generate more heat. As sows produce more pigs per litter, heat production also increases. Brumm estimates that the relative production improvements of growth and overall health translate to 10-15% greater heat production by pigs than their counterparts just 10-20 years ago.

    Brumm has built a spreadsheet that models heat flow in hog barns. “Heat is generated by growing pigs or lactating sows and lost through the insulated building shell and fans. Even in the northern climates, ventilation systems are often operating to remove heat from a barn, so it's a big deal to get minimum ventilation right because it reduces the propane needed to heat the building,” he says.

  • Attic inlets

    Clearly, to move air out, you've got to get air in, and Brumm's rule of thumb is 1 sq. ft. of attic inlet for 400 cfm of fan exhaust.

    Fan settings are often blamed for ventilation mistakes, but improper inlet sizing is another common problem.

    “In many situations, improper sizing isn't related to the ceiling inlets, but rather the attic inlets,” he says. “Ceiling inlets are sized to provide air at 0.05-0.10 in. static pressure, the same static pressure used to size fans. To avoid problems with restricting ceiling inlets, the openings into the attic space must be larger so there is minimal static pressure restriction prior to the ceiling inlet.”

    Ridge vents are not the answer. “Air blowing across the top of the ridge vent creates a negative pressure on the backside, and the uplift increases the faster the wind blows. A 10-mph wind blowing across the ridge equates to 0.05 in. of static pressure uplift, while a 20-mph wind equates to 0.2 in. static pressure. Static pressure restrictions are additive in a ventilation system,” Brumm says. He credits Iowa State University agricultural engineer Jay Harmon for doing the math that shows the uplift created by the wind blowing across a ridge vent.

    “That's why we don't talk about ridge vents as inlets. If it was entirely calm, they'd work great. They're important because they neutralize pressure in the attic from wind, so you have to have them for pressure release or you'd blow all of your inlets open, but don't count on them as inlets,” he reinforces.

    “Build the attic inlets right and clean them. Walk your sites and look at the inlets. You'll be amazed at how it restricts air (inlet) and air flow,” he adds.

  • Pit lids

    Pumping manure pits after harvest is a race with Mother Nature. Pit pumpers are busy. When pit lids are not replaced correctly, they become air inlets.

    “If you have a wean-to-finish room with two, 24-in. pit fans running at 50%, you need a total of 7.5 sq. ft. of total air inlets to get 800 ft./min. air inlet velocity at the ceiling inlet,” he says. “A common 3 ft. x 6 ft. 8 in. walk-in door is 20 sq. ft., so 7.5 sq.ft. is a bit more than a third of a door opening. If the air inlets in the room are sized properly, but you can't get good air distribution in the room at minimum ventilation settings, check the pit covers,” he suggests. “A 2-in. crack in the 4-ft.-wide pump-out ports will make a big difference.

    “After pit-pumping is done, walk the barns to make sure pit lids are on tight. A can of spray foam works great to get them tight,” he adds.

  • Clean fans

    “Dirty fans and shutters can reduce air flow by up to 40%. We do a wonderful job of washing all the fans on the (inside) walls whenever we power wash, but some pit fans have never been cleaned,” he declares.

  • Furnaces

    “If you want something quick and easy to take home to your clients that will make a difference, this is it: Furnaces in our hog buildings are big enough if they shut off,” he says flatly.

    It's not unusual for the price of a 250,000-Btu. furnace to be just $50 more than a 60,000-Btu furnace, so producers most often choose the big one as a better buy.

    “Wrong,” says Brumm. “Your goal with furnaces should be: the longer the furnace runs, the more uniform the heat distribution in the room. You don't want big up-and-down temperature spikes.”

    What about variable-output furnaces? “When the blue valve is between the flame and the control module, it is not a shut-off valve, it's a variable-output valve. When the valve is manually turned parallel (to the gas line), you're at 100% of the rated Btus (of the furnace); when it's turned sideways (to the gas line), you're at the minimum Btu output.

    In other words, a 250,000-Btu furnace can often be turned down to 170,000 Btu. This time of year (September), every furnace in every hog barn in North America should be turned down. When do you turn it to high? When it doesn't shut off on a cold day,” he says.

    As a footnote, he reminds: “Each pilot light burns about ? gal. of propane a day.” Turn them off during the summer months.

  • Understand and check emergency ventilation systems

    “I mention this in every talk I give on ventilation,” says Brumm. “As an industry, we have not done a good job of educating our pig owners and contract growers about the value of maintaining our emergency systems.

    “Do you understand the emergency heat relief thermostats in your barn?” he asks. “Many were set at 90° F when the barn was built, and they haven't been touched since.

    “In theory, the emergency thermostats for heat release should be set to come on when it is 5° above the device temperature they are controlling. That means, as you change set points, you change emergency thermostat check points.

    “And don't forget to hook devices up!” he urges. Brumm says many of the curtain magnetic drops he sees are unhooked. “That's clear negligence in the case of pig deaths,” he warns.

    Curtain drops and generators need to be tested frequently; keep a dated and signed log of the test. They should be tested quarterly.

    You can't use the hour meter on the generator (as a safety check); it only proves the generator ran. You have to test the transfer switch. Generally, these are done monthly. Many have weekly auto starts; if you're on the site and witness the flicker of the lights when the transfer switch functions, date and sign that you were there, he suggests.

    “If an event happens and pig deaths occur, that is proof of maintenance of the system. Otherwise, it's your word against the insurance company lawyer,” he says. “Understanding emergency ventilation is a big deal in this industry.”