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. (www.bess.uiuc.edu; 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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