Although an instrument that provides velocity reading, shown here, is highly useful, a simple small streamer can also help troubleshoot.
In a well-managed ventilation system, the desired air speed exiting ceiling inlets is 800 to 1000 feet per minute (fpm). The handy air speed monitors described here (Figure 1) are a cheap, easy, and adequate way to estimate air speed. The monitors can be made by hanging strips of plastic film in the air stream coming from the inlet. The length, weight and number of layers of plastic can be varied depending on the air speed you desire to monitor. Placed near the ceiling inlets of a livestock facility, the monitors will indicate if the air speed is high enough to allow fresh air to mix with old air as it travels across the building.
Figure 1. Perspective view of air speed monitor.
- paper clips
- duct tape
- overhead projector transparency sheets (3M transparency film for plain paper copiers (product #PP2200) was used in the prototype)
- paper hole punch
- brightly colored permanent magic marker
Directions for each monitor
- Cut overhead sheets into 1″x3 1/2″ strips as shown in Figure 2.
- Color strips with a brightly colored permanent magic marker for enhanced visibility.
- Punch two holes at one end of each strip keeping the distance from the holes to the other end of the strip at three inches.
- Open up two paper clips by unfolding them once in the center.
- Hang one, two, or three of the plastic overhead strips on the two paper clips. It is essential that the plastic strips swing freely.
- Cut a small piece of cardboard, hook the opened paper clips around cardboard, and tape the paper clips to stabilize them.
- Securely tape or fasten cardboard flat to the ceiling four inches from the inlet so that the plastic strips can move freely in the breeze (Figure 3).
*Note: The weight (as affected by width and length) and freedom of movement of the transparency strips are critical in the accuracy of these air speed monitors
Figure 2. Template for air speed monitor plastic strip.
Figure 3. Side view of air speed monitor in room.
Read the Monitors
A broad range of air speeds can be monitored if all three types of air speed monitors are placed in close proximity and are compared to drawings in Figure 4. If the wind speed is 500 to 600 fpm, then a single layer plastic strip will be nearly touching the ceiling as a result the air movement (see Figure 4A). To determine higher wind speeds use a double layered plastic strip. This will nearly touch the ceiling at air speeds of 700 to 800 fpm as seen in Figure 4B. To determine even higher air speeds, hang three plastic strips from the paper clips. These will nearly touch the ceiling at air speeds of approximately 1000 fpm as seen in Figure 4C. The strips do not have to be glued together.
Realize that these simple monitors provide “ballpark” estimates of the air speed issuing from a ceiling inlet. They can be an effective visual check for adjusting inlets to provide air mixing and distribution. These monitors work for inlet opening widths of 1/2- inch and wider.
For more information on ventilation inlets, please refer to fact sheets: Inlets for Mechanical Ventilation Systems and Self-adjusting Baffle Inlet to Improve Air Distribution.
Eileen F. Wheeler, Professor, Agricultural and Biological Engineering; Jason Martin, Senior, Poultry Science