The hard choices during tunnel ventilation

Turning pit/sidewall fans off during maximum ventilation can reduce energy usage with minimal impact.

June 16, 2021

5 Min Read
End of a hog barn with a wall of fans

The goal of tunnel ventilation is to pull air down the length of the room at a high airspeed to create a “wind chill” effect for the pigs to keep them thermally comfortable. There are generally three to four tunnel stages to provide a transition during warm/hot weather before the maximum ventilation rate is achieved (last tunnel stage). For each tunnel stage, decisions have to be made on the operation of pit fans and inlet opening percentage. There is often a lot of discussion on these topics; hence, the goal of this article is to share some results of a field study exploring the impact of pit fans on/off, and inlets open/closed during tunnel ventilation stages.

The 5,000-head wean-to-finish facility in north-central Iowa was U-style with two buildings (each with two rooms) connected by a common hallway and entry office. The facility was oriented so that the long axis was parallel to east/west. Each building was nominally 193 ft. by 101 ft. with one common attic air space and two rooms (each room: 193 ft. by 50 ft.) separated by a solid interior center wall down the length of the building. There were 20 automated biflow ceiling inlets in two rows. Two rooms were equipped with four variable 24 in. diameter pit fans located on the center pit annexes and the others with two 24 in. diameter sidewall fans, resulting in similar airflow capacity based on manufactor specifications. Warm/hot weather ventilation was achieved with one 36 in. diameter exhaust fan and four 54 in. exhaust fans on the east-facing wall, all equipped with standard interior PVC shutter and outer PVC cone.

Several field tests were conducted last summer to evaluate the objectives. Two rooms featured the pit or sidewall fans off (SF/PF OFF), and the other two rooms featured the pit or sidewall fans on (SF/PF ON) during the last two tunnel stages. Also, during the last tunnel stage, the ceiling inlets were closed, opened at 25%, and opened at 50% to test the impact on room airspeed and temperature. Testing was only completed when the rooms were in their final stage of ventilation, with all designated fans running at full capacity and intake curtains fully opened. In each room, eight temperature dataloggers were evenly distributed throughout the room. Room airspeed was recorded manually with a portable environmental meter. The meter was held at two heights, approximately gate and eye level, at six different locations throughout each room, approximately 40, 60, and 80% down the length of the facility on each side of the center alleyway. Readings over a 30 second period at each height and location were manually averaged and recorded on a weekly basis.

Airspeeds directed parallel to the length of the facility rooms were collected on five different dates through warm weather ventilation for the inlets fully closed variation. Measurements were averaged amongst the six testing locations. Average airspeeds were (mean ± SD) 433 ± 11 fpm, 374 ± 40 fpm, 393 ± 40 fpm, and 295 ± 138 fpm for room 1, 2, 3, and 4, respectively.

Airspeed was the lowest and most variable in room 4 (PF OFF), the south-facing room of the facility, while it was highest and least variable in room 1 (SF ON), the north most room of the facility.

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Outdoor wind conditions most likely had a major impact on airspeed measurements. This is the likely cause of the low outlying room airspeed measurement in room 4 on this date. Average daily electrical usage was (mean ± SD) 3.8 ± 0.1 kW, 3.9 ± 0.2 kW, 3.4 ± 0.08 kW, and 3.5 ± 0.2 kW for room 1, 2, 3, and 4, respectively. An estimated 0.4 kW decrease in electrical usage per day was the likely result of turning off sidewall and pit ventilation fans as facility rooms operated in higher ventilation stages.

Airspeed directed parallel to the length of the facility was measured on two different dates for both the 25% opening and 50% opening during modified ceiling inlet operation towards the end of the animal growth cycle. Averages were taken across all rooms and were compared back to that of the five dates of testing with inlets in the closed position. Airspeeds were (mean ± SD) 396 ± 42 fpm, 344 ± 12 fpm, and 365 ± 15 fpm for the closed, 25% open, and 50% open inlet operation testing dates.

Room temperature was also compared for each phase of inlet operation. Due to its high dependency on outdoor temperature throughout this time, an offset of average room temperature and outdoor temperature was calculated. Temperature data was selected from the week prior to inlet modification and compared to the one week of each alternate opening percentage operation. All rooms were again averaged, with resulting room temperature offsets from outdoor temperature of (mean ± SD) 4.0ºF ± 1.1ºF, 5.4ºC ± 2.5ºF, and 4.5ºF ± 2.2ºF for the closed, 25% open, and 50% open inlet operation.

The key take-homes from this short study show that turning pit/sidewall fans off during maximum ventilation can reduce energy usage with minimal impact on room temperature and airspeed. Although opening the inlets did not impact room temperature, airspeed was negatively affected and inlets should be closed during the last two tunnel stages.


Sources: Sydney Klimesh and Brett Ramirez, Iowa State University, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

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