But as Mike Brumm, an independent consultant from North Mankato, MN, and a team of four Extension specialists began taking measurements for a complete energy audit of the facility, it soon became apparent that their five senses didn't begin to capture what was really going on with the facility's ventilation system that day.

The group's plan was to complete an energy audit to be used as a case study for ventilation workshops.

The 41-ft.-wide, grow-finish barn had two, 1,000-head rooms split by a work room at the center, where a controller moderated heat and ventilation.

When the group conducted a walk-through evaluation, the pigs had been in the facility for 13 weeks and marketing was scheduled to begin soon. Daily gains were averaging 1.60 to 1.85 lb. with feed conversion ranging from 2.65 to 2.95 lb. of feed per pound of gain.

“Once we began gathering data, we could see something wasn't right in the facility,” Brumm notes.

Each fully slotted room had four, 24-in. pit fans evenly spaced along the south side and a fifth fan on an end wall. Two pit fans were variable speed; the remaining three were single speed.

Fans were rated at 7,010 cfm at 0.05 in. static pressure. All fans had shutters.

Twelve ceiling inlets were evenly spaced over the center aisle of each 1,000-head room. The manufacturer's rating was 3,120 cfm per inlet. Each inlet had two baffles with 24 × 3.5-in. openings. Table 2 shows inlet settings for minimum ventilation rates.

The ventilation system was designed to provide about 35 cu. ft./min./pig (cfm/pig), which calculated: 7,010 cfm/fan × 5 fans/1,000 head = 35.0 cfm/pig fan capacity, and 12 × 3,120 cfm/inlet/1,000 hd = 37.4 cfm/pig inlet capacity. An Airstream controller averaged the readings from two temperature probes mounted in each room.

The controller temperature was set at 67°F. Minimum ventilation was provided by two, variable-speed pit fans with the motor curve 4 at 60% and 1°F bandwidth (Table 1).

At Stage 2 ventilation, two single-speed pit fans kicked in with 1°F differential. And, at Stage 3 ventilation, a single-speed wall fan came on at 1°F differential.

Problems Arose

The team soon discovered that incorrect settings on the weight-adjusted air inlet baffles were compromising the facility's ventilation system and causing a host of problems.

“That type of inlet is notorious for bouncing on windy days,” Brumm explains. “The producer had locked the inlets so they only opened so far because they were causing rapid changes in the static pressure of the facility. That's the correct thing to do in windy weather conditions, but when he forgot to unlock them, that's when the ventilation problems started.”

The building's normal, fan-assisted ventilation capacity was 35 cfm/pig. With the inlets restricted, the rate dropped to 20 cfm/pig.

“Because there wasn't enough air entering the facility, the fans were being starved. Under those conditions, static pressure increases, and that triggers an increase in fan speed and fan staging because they have to work harder to move the proper amount of air,” Brumm explains.

Despite the fans working harder, the temperature inside the facility began to rise, requiring more electricity. At that point, the controller turns on another fan.

“Now, you're using even more electricity, but the air still isn't coming in at a rate to meet the fans' needs. Static air pressure is still very high. If the temperature continues to rise, the next step is the controller drops the curtain,” he says.

The facility's curtain overlapped the header by 3 in. The curtain controller was set to move the curtains at a rate of 1 ft./min. With cycle settings at 15 seconds, the curtain opened 3 in. during each cycle and then stopped for two minutes to gain a temperature reading before moving again. The controller's dead-band, the variable difference between when the heater shuts off and fans began to increase speed, was 1.5°F.

Normally, fans shut off when the curtain opens just a few inches. This owner had modified controller settings so the fans stayed on until the curtain was open 10-12 in.