Make Your Own Ceiling Inlet Air Speed Monitors

In  well-managed animal housing, the desired speed of fresh air at ventilation inlets is 800 to 1000 feet per minute (fpm) or 4-5 m/s. This air speed provides adequate mixing of incoming and room air and distribution of that air across the facility. The handy air speed monitors described here (Figure 1) are a cheap, easy, and verified way to estimate air speed. They provide a visual check on ventilation performance. The monitors can be made by hanging strips of plastic film in the air stream coming from the inlet. The dimensions, weight and number of layers of plastic can be varied depending on the air speed you desire to monitor. The sample monitors offered here were designed using accurate, although relatively expensive, air velocity monitors (hot wire and vane anemometers) to achieve desired air speed. Placed near the ceiling inlets of a livestock facility, the monitors will visually indicate if the air speed is high enough to allow fresh air to mix with old air as it travels across the building. The monitors are particularly useful for lower ventilation rates used during cold and cool weather.

Materials needed

• cardboard
• paper clips
• duct tape
• overhead projector transparency sheets (3M transparency film (product #PP2200) was used in the prototype)
• scissors
• paper hole punch
• brightly colored permanent felt-tip marker

Directions for each monitor

1. Cut overhead sheets into 1 inch x 3.5 inch (2.5 cm x 9 cm) strips as shown in Figure 2.
2. Color strips with a bright permanent felt-tip marker for enhanced visibility.
3. Punch two holes at one end of each strip keeping the distance from the holes to the other end of the strip at 3 inches (760 mm).
4. Open up two paper clips by unfolding them once in the center.
5. Hang one, two, or three of the plastic overhead strips on the two paper clips. It is essential that the plastic strips swing freely.
6. Cut a small piece of cardboard, hook the opened paper clips around cardboard, and tape the paper clips to stabilize them.
7. Securely tape or fasten cardboard flat to the ceiling 4 inches (10 cm) 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. Other dimensions can be used once air speed is verified with an accurate anemometer.

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 air speed is 500 to 600 fpm (2.5 - 3 m/s), then a single layer plastic strip will be nearly touching the ceiling as a result the air movement (see Figure 4A). To determine higher air speeds use a double layered plastic strip. This will nearly touch the ceiling at air speeds of 700 to 800 fpm (3.5 - 4 m/s) 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 (5 m/s) 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 fresh air 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 (125 mm) and wider.

Figure 4. Air speeds indicated when using these simple monitors. Metric: A. 2.5-3 m/s. B. 3.5-4 m/s. C. 5 m/s.

For more information on ventilation inlets, please refer to:

• Inlets for Mechanical Ventilation Systems in Animal Housing
• Self-Adjusting Baffle Inlet to Improve Air Distribution

Eileen Fabian (Wheeler), Professor, Agricultural and Biological Engineering; Jason Martin,former Poultry Science undergraduate, currently, Heritage Poultry Management Services.