Extension > Agriculture > Dairy Extension > Facilities > Ventilating Calf Barns with Tube Systems
Ventilating Calf Barns with Tube Systems
Published in Dairy Star April 2, 2010
Some dairy producers and heifer raisers are installing tube systems to help ventilate remodeled barns used for raising heifers. Important decisions need to be made when sizing and installing them. Additional decisions need to be made to complete the ventilation system.
Table 1. Airflow per tube (MWPS-32, 1990) |
|
|---|---|
Tube diameter (inches) |
Airflow (CFM) |
8 |
210 - 280 |
10 |
320 - 440 |
12 |
470 - 630 |
14 |
640 - 860 |
16 |
830 - 1,100 |
18 |
1,060 - 1,400 |
24 |
1,850 - 2,500 |
Table 2. Airflow per hole (MWPS-32, 1990) |
|
|---|---|
Hole diameter (inches) |
Airflow |
1 |
2.7 |
1.25 |
4.2 |
1.5 |
6.1 |
2 |
11 |
2.5 |
17 |
3 |
24 |
The simplest tube system has an axial fan connected to a long plastic tube with holes distributed uniformly along the tube. The fan pushes clean fresh outside air into the tube, which exits through distribution holes along both sides of the tube. Airflow through the tube and out distribution holes is complex but simple systems are useful. Uniformly sized and distributed holes do not provide uniform air distribution; more air exits the tube at the closed end than the fan end.
Tube systems should be used to distribute clean fresh air taken directly from outdoors through a wall or out of the attic. Air for calves should never be taken from an area housing older heifers or cows. The air from older animals usually contains airborne pathogens and gases that can cause disease or respiratory stress in pre-weaned and weaned calves.
Tubes should not be used to recirculate or mix air in a calf barn. If the tube is allowed to recirculate air, it will collect dust and microorganisms in the bottom of the tube. While tubes can be cleaned, they are seldom cleaned enough to prevent disease transmission to the next batch of calves.
Key tube system decisions include fan airflow rate, tube diameter and length, and number, size and location of distribution holes. The guidelines presented here are based on information in the Mechanical Ventilating Systems Handbook (MWPS-32) by MidWest Plan Service.
- Tube systems are sized to provide the continuous minimum cold weather ventilating rate for a barn or room. The cold weather ventilating rate provides adequate fresh air to manage humidity levels in the calf barn. Dairy calves tolerate cold temperatures quite well if they have adequate nutrition, access to clean water, a clean dry and comfortable resting area, and adequate draft-free fresh air. In extreme cold, calf blankets can be used if calves appear chilled and are not performing well.
- Ventilating rates can be based on the number of calves to be housed. The cold weather ventilating rates for dairy calves is 15 cubic feet per minute (CFM). So a room with 50 calves would need a minimum ventilating rate of 750 CFM.
- The distribution tube diameter should be large enough to minimize pressure drop along the tube. This is done by having the duct diameter large enough so that the air velocity in the tube is 600 to 800 feet per minute. Based on Table 1, a 14-inch diameter tube or larger is needed to handle the 750 CFM needed to ventilate the example barn housing 50 calves.
- Distribution tube length can vary depending on the room dimensions.
- Holes are placed on both sides of the tubes at either the 9 and 3 o'clock positions or the 8 and 4 o'clock positions. The number and diameter of the holes is based on the airflow rate. Longer tubes have the same number of holes as shorter tubes if the airflow rates are the same but the holes will be spaced further apart.
- Airflow rate per hole varies by hole size (Table 2). For example, 1-inch diameter holes can allow 2.7 CFM per hole and 2-inch diameter holes allow 11 CFM per hole. To distribute 750 CFM along a 40-foot long tube using 2-inch diameter holes, 68 total holes are needed; 34 distributed evenly along each side of the tube every 13.7 inches.
- Tube systems can distribute fresh air from either the attic or directly from the outside. The opening into the attic should be sized large enough to keep the air velocity below 400 feet per minute. For a fan taking 750 CFM from an attic, the opening should be 1.9 square feet. A square opening 1.4 foot by 1.4 foot or larger would do the job. If fresh air is taken from the attic, it is essential that there are openings for fresh air to enter the attic. The opening into the wall is sized to mount the fan.
- In addition to the tube system, exhaust fans are needed in the walls to exhaust air from the barn and maintain a slight negative static pressure to avoid pushing moisture into the walls. As the weather warms up and additional ventilation is needed, more exhaust wall fans need to turn on and inlets need to open up to provide up to 100 CFM per calf in hot weather.
Fresh air tube system in a calf barn with automatic feeders.
