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Ventilation

This section was written in collaboration with Dr. Hongwei Xin, Professor, Department of Agricultural and Biosystems Engineering and Department of Animal Science, Iowa State University, Ames, Iowa, USA.

Ventilation is essential to ensuring the proper micro-environment for birds comfort and health throughout the production cycle. During cold weather, the role of ventilation is to remove the extra moisture and noxious gases (primarily carbon dioxide, CO2, and ammonia, NH3) in the barn generated by the birds, manure, and combustion where unvented heaters are used (e.g., in pullet or certain cage-free layer houses). The indoor relative humidity (RH) should be kept in the range of 40 to 60%, although occasionally higher RH (e.g., 70 to 75%) during part of the day will not adversely affect the birds. Too low RH (i.e., too dry air) in the barn can lead to dusty environment and is undesirable for the birds' respiratory health. Conversely, too high RH (too moist air) can lead to water condensation in less insulated barns and promote growth of microbial organisms.

The NH3 concentration should be kept below 25 ppm, especially for pullets, because high NH3 levels can adversely affect bird health (respiratory system and eyes), feed intake, and production performance. The recommended ventilation rate (as shown in the table below) should be adjusted to achieve the target thermal environment (20 to 29°C [68 to 85°F] depending on age) and air quality. With the proper control of RH and NH3 concentration, the indoor CO2 level during cold weather generally falls below 3000 ppm, which is much lower than the recommended threshold for human or animal health.

During warm weather, the role of ventilation is to remove the extra bird body heat to maintain the comfortable indoor temperature. The amount of ventilation used for temperature control (typically 3.7 to 5.6 m³/hour per kilogram of body weight or 1.0 to 1.5 ft³/minute per pound of body weight) far exceeds the amount of air needed to control gaseous levels in the barn. Hence, in summertime, indoor NH3 or CO2 levels are not of concern.

Provision of sufficient ventilation or fan capacity
A common mistake is to assume a fan will deliver the amount of air as specified by the manufacturer without considering the operating static pressure or conditions of the fan (e.g., belt tightness, blade or shutter cleanliness). For instance, a 1.2-m (48-in) diameter fan is commonly considered to have an airflow capacity of 30,600 m³/hour (CMH) or 18,000 ft³/minute (CFM). In reality, when operating at 25 Pa (0.1 inch water column) static pressure in a poultry barn, the fan may only deliver 18,700 CMH or 11,000 CFM, corresponding to 61% of the nominal capacity! Moreover, it is not uncommon that static pressure in some barns reaches 50 Pa (0.2 inch water column), which will reduce the airflow capacity even more. Hence, when determining the number of fans needed for the barn, one must take into consideration the influence of static pressure and degradation of the fan capacity over time due to motor wearing, loose belt, and dirty blades or shutters. Otherwise the barn will end up being considerably short of ventilation capacity. Running fans under higher static pressures, such as 50 Pa, unduly increases workload of the fan motor and significantly reduces the fan performance efficiency, i.e., CFM output per unit of electric energy input.

Proper distribution of the airflow
Uniform distribution of the ventilation air to avoid dead zones or cold spots throughout the barn is as important as providing sufficient ventilation capacity. Uniform air distribution is attained by proper placement and operation of the barn air inlets and use of proper building static pressure. Under cold weather and for young birds, air should be distributed uniformly to the entire bird-occupied zone with minimal drafts. This is the reason for using cross-ventilation, as opposed to tunnel ventilation, which would create undesirable end-to-end temperature gradients or drafts, during cold weather. In contrast, for temperature control under warm and sometimes humid climate conditions, it is beneficial to increase air velocity over the birds to enhance body heat dissipation. The higher air velocity will add the wind-chill effect to the birds and reduce the impact of humidity, hence lowering the effective environmental temperature. Tunnel ventilation is typically used to achieve the higher air velocity. When air temperature exceeds certain level, say 35°C (95°F), increasing ventilation or air velocity alone will not achieve the needed cooling. Under such circumstances supplemental cooling, e.g., fan-pad evaporative cooling or high-pressure fogging needs to be employed to ensure bird thermal comfort.

Below are suggested ventilation rates for Hy-Line W-36 and Hy-Line Brown measured per 1000 birds.

See also the House Temperature and Relative Humidity section.

Suggested ventilation rates for Hy-Line W-36 (SI units)1

1The air quality and bird comfort must be considered when setting the ventilation rates.

Suggested ventilation rates for Hy-Line W-36 (Imperial units)1

1The air quality and bird comfort must be considered when setting the ventilation rates.

Suggested ventilation rates for Hy-Line Brown (SI units)1

1The air quality and bird comfort must be considered when setting the ventilation rates.

Suggested ventilation rates for Hy-Line Brown (Imperial units)1

1The air quality and bird comfort must be considered when setting the ventilation rates.

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