Better Barn Features for Poultry
By Harry Huffman P. Eng. Agricultural Engineer
Features New Technology ProductionA ventilation engineer’s perspective
To ensure a new poultry building is the best it can be from a
production point of view, a farmer needs to consider the many options
and variations available and assemble a team of professionals to help
him achieve this goal.
A ventilation engineer’s perspective on making a poultry building the best it can be
DESIGN FLAW The metal ceiling liner with ribs is causing major obstruction to incoming airflow. Advertisement
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To ensure a new poultry building is the best it can be from a production point of view, a farmer needs to consider the many options and variations available and assemble a team of professionals to help him achieve this goal. These professionals will include a structural engineer, an agricultural engineer or consultant with ventilation design expertise and a respected building contractor. All of these professionals should have experience within the poultry building industry to avoid a number of common design and construction mistakes that can affect bird performance and the longevity of the structure. I am writing this article with my “ventilation” hard hat on.
If the land is reasonably level and allows an orientation choice, then the side of the building to be used for air intake needs to be considered. If the air intake is located on the south or particularly the west side of the building, then the sun can preheat (or over-heat) the incoming fresh air depending on the season. Alternatively, an air intake located along the east or north-facing wall will be cooler during hot summer conditions. If some passive solar heating is desired for the incoming winter air, then the air intake should be located along the east or south facing sidewalls.
Many buildings are oriented to limit prevailing wind pressures on the exhaust fans. But the wind can blow from any direction and needs to be addressed regardless of building orientation. Good weather hoods should be installed on all cold weather fans (at least stage 1 and 2 ventilation). Similarly, the air intake needs to be adequately protected from wind with a continuous hood and wind stop.
While an interior service or utility room is a little more economical than a small attached structure, it very often interferes with good cross-flow ventilation as well as full width tunnel ventilation. The ideal location for an exterior, add-on service room is at the front corner of the building along the sidewall housing the exhaust fans. If it must be located within the main structure, then it should be situated at the front corner on the exhaust fan side.
Buildings up to 40 feet wide ventilate reasonably well regardless of the ventilation system choice. However, wider buildings need to consider ventilation options that enhance air movement across the entire width of the building. This may include an air inlet along both sides of the building or a double-baffle board along one side to ensure adequate airflow over all of the birds. Tunnel ventilation is a good summer time option to increase the air speed over the birds and help reduce heat stress.
Regardless of building width, all poultry barns with floor housed birds should be equipped with internal air circulation fans to ensure good air mixing and air distribution during the three cooler seasons. These fans will eliminate temperature differentials and stratification as well as ensuring all birds receive some fresh air. Additionally, internal air circulation helps dilute the carbon dioxide concentration at floor level, which along with water vapor is produced by the birds’ respiration. Lastly, these circulation fans help transport a consistent sample of mixed barn air to an operating point of exhaust.
All poultry buildings should be insulated and sealed extremely well. Most poultry buildings require supplementary heat during cold weather (year round for brooding) and therefore all controllable heat losses should be minimized. Interestingly, the largest heat loss in all poultry buildings is through the exhaust fans (60%+). This fact makes it essential to size and manage the exhaust fans appropriately to control heating costs.
The air intake opening into the building must be sufficiently large to handle the maximum ventilation capacity at a low static pressure level such that the proper air circulation pattern can be created and maintained year round. A good rule of thumb is to allow 2 square feet of opening for every 1000 CFM (cubic feet per minute) of ventilation fan capacity. This net opening must not be compromised with a weather hood and/or bird screening which restricts the airflow before it even reaches the air intake.
The incoming airflow needs to be jetted across the ceiling at approximately 800 to 1000 feet per minute to establish the desired air circulation pattern and ensure good mixing with the room air. This requires the air inlet baffle board to be installed at an angle ranging between 30 and 60 degrees to the ceiling and wall intersection with 45 degrees being ideal. If the baffle board angle falls outside the acceptable range, the incoming airflow will not flow across the ceiling properly.
The most common type of ventilation problem created during barn construction and equipment installation is an obstruction to airflow across the ceiling surface. An obstruction is anything placed directly in the travel path of the incoming air stream, which causes the air to become turbulent and/or deflect down into the room air space. These obstructions take many forms and are caused by the building contractor and a variety of trade’s people.
Typical obstructions include: A ribbed ceiling liner installed with the ribs at right angles to the required airflow as shown in Figure 1. Applying appropriate ceiling strapping will allow the ribbed material to be installed parallel to the airflow and not cause any interference.
An electrical conduit running lengthwise on the ceiling for wiring light fixtures, air inlet actuators, fan motors and feed line motors create an excellent airflow deflector.
A water line attached to the ceiling surface. Ideally all piping should be kept at least 4-feet and preferably 8-feet from the air inlet.
A gas line suspended from the ceiling. A longer hanger can be used to provide 4 inches of clearance over the line for the incoming air jet to travel unhindered.
Very often the air inlet actuator is located at the front end of a long side air inlet such that the control cable runs the whole length of the inlet baffle board. This results in a cable length that can often be 200-feet or more. These long cables tend to stretch over time and temperature changes will alter their length. This means that the air inlet baffle board does not open and close uniformly along its length and requires ongoing adjustment. A simple correction is to ensure that the cable actuator gets positioned midway along the inlet baffle board to reduce the cable length by half. An ideal maximum pull length would be in the range of 100-feet or less.
You should consider the installation of some form of evaporative cooling to reduce the negative effects of heat stress during hot weather. Both low and high-pressure systems have proven to be quite effective in reducing heat stress when properly managed.
Lastly, it makes sense to use durable materials for both constructing the building and equipping it. All poultry buildings should last at least 20 years without any major repair. Of course, regular maintenance and an on-going rodent control program are essential to keep the building in good repair.
Your team of professionals can help you construct a poultry facility that will perform well for the birds and you. Be sure to use their expertise and avoid building mistakes into your new facility.
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