Chapter 8 - Providing minimum ventilation

The cold weather minimum ventilation rate in broiler barns is often far below the capacity of a single-speed, 36- or 48-inch fan. Continuously modulated airflow, such as that provided by a variable-speed fan, is preferred for varying the cold weather airflow. It takes a tightly-constructed house to allow one or two smaller fans to create the static pressure necessary for proper inlet functioning throughout a large poultry house. Since not all houses are tightly constructed, many use a higher capacity fan (such as a 36-inch) on an interval timer for cold weather ventilation. However, the broilers are breathing, water is evaporating, manure gases are volatilizing, and heaters are venting continuously while fresh air is only added a fraction of the time.

Timers

On-off electrical switches activated with a clock motor, or interval timers, achieve variable airflow rates by running for only a part of each interval. They are manually set to operate a specified number of minutes every five minutes. Some systems use a ten-minute interval, but this results in undesirable temperature swings of roughly 2-5°F. Combustion by-products from unvented heaters may also build up to unacceptable levels during the off-period. These fluctuations can affect broiler comfort and health. Consequently, five-minute times are recommended over ten-minute timers. However, ten-minute times may be an appropriate selection depending on how quickly air inlets respond after the fan is activated.

Ammonia levels should be spot-checked one minute before the timer is set to cycle back on. The air should be sampled to broiler level, about one foot off the ground. A hand-held sampler pump and indicator tube, or a passive tube are common sampling tools (see Chapter 14 on litter amendments for more information on measuring ambient ammonia levels.) Readings over 25 ppm ammonia indicate that the minimum ventilation rate needs to be increased to reduce ammonia build-up. In these cases, the on-time interval of the timer should be set to increase the amount of time the fan is on.

It is important that a producer not rely on his or her sense of smell to determine ammonia levels. A person’s sense of smell will desensitize to ammonia over time. Always use a measuring device to determine levels.

Troubleshooting

Many problems during cool and cold weather can be traced to inappropriate ventilation rates. Poor broiler health, respiratory problems, and breast blisters are common with poor ventilation.

An excessive ventilation rate causes:

• Excess fuel use
• Temperatures that are too cool; inability to maintain blood temperatures (Low temperatures could also be caused by inadequate heater capacity)
• High concentration of dust

An insufficient ventilation rate causes:

• High concentrations of ammonia and air contaminants
• Areas of excessive moisture; soggy litter (could also be a drinker problem)
• Condensation on the interior surface (could also be inadequate insulation)

Poor air distribution (improper inlet function) causes:

• Drafts
• Uneven temperatures; cold spots and/or hot spots
• Areas of excessive moisture, soggy litter