Designing Ventilation and Airflow to Optimize Bird Comfort

In all regions and especially tropical countries, house design is critical to ensure optimal airflow for bird cooling and comfort. When designing a modern broiler house the first question one considers is the optimum floor area for the best return on investment (ROI). New longer and wider houses challenge the ventilation system’s ability to produce uniform conditions the full length of the house.

Secondly, and equally important, is what air exchange and air speed is needed to keep the birds comfortable, and how will this impact energy costs? The primary goal of broiler farmer is to stimulate feed consumption from the moment the chicks arrive on the farm to when they leave for slaughter.

The first seven days in the life of a chick are the most important. An extra gram then can be equivalent to 5 grams or more at 35 days. The brooding period sets the precedent for good performance and extra effort then will be rewarded in final flock performance. To ensure a good start, the grower must provide an environment that ensures optimum immediate intake of feed and water.

The other most challenging period, especially in the hot season is the grow-out phase – after 25 days. Birds are fully feathered and hot ambient conditions will challenge feed consumption. Capital investment is often driven by the need for high ROI or fast paybacks.

Access to good quality equipment, high construction costs, government import tariffs and freight costs can limit choice. Investment decisions are often made without optimizing design and airflow requirements needed to ensure optimum bird performance and financial return. In today’s low-margin environments, returns depend on achieving performance in line with genetic targets. These are some essential design considerations:

1. Well insulated smooth ceilings and walls.

2. Good quality inlets for minimum and transition ventilation

3. Adequate static pressure control, by thorough sealing of houses. All new projects should be commissioned only after pressure testing.

4. Tunnel fan choice based on efficiency – not cost! Fan choice will be the most important design decision, especially in hot climates.

The roof and/or drop ceiling insulation is one of the most important aspects of any new house project. In most tropical regions drop ceilings are not insulated. The best option is to install insulation either on top of the drop ceiling or against the roof.

The biggest challenge for houses longer than 120m is maintaining an acceptable temperature pickup from the front to the back of the house during the summer months with big birds - commonly referred to as the ΔT. The level of bird comfort ultimately drives daily feed consumption. Even temperature distribution the length of the house will ensure uniform feed intake and slaughter weight uniformity.

The amount that the air in a house heats up down the length of the house depends primarily on three factors:

  1. Metabolic heat added by the broilers
  2. How quickly the air in the house is exchanged.
  3. Thermal properties of the house

Heat flows through surfaces from hot to cold, entering the house through the ceiling, sidewalls and curtains. The higher the resistance to flow or higher the R value of the surface, the lower the emissivity. As well as entering the house through all surfaces, heat is also produced by the birds, which are by far the greatest contributors to heat load.

But the value of an insulated roof or drop ceiling cannot be underestimated. In modern long houses it is vital from both a bird comfort and operational cost perspective. For example, improving ceiling R value from a R2 (simple plastic drop ceiling with no insulation) to a R10 should improve the ΔT by a possible 1 or 2 degrees C, thus reducing the tunnel fan or air exchange capacity needed to achieve our goal of having an absolute maximum of 2.8ºC temperature pickup on the hottest day of the season with the biggest birds.

A broiler house should have a minimum insulation in the roof of R 8-10. Heat is removed from the house by rapidly exchanging the air in conjunction with evaporative cooling systems. If the temperature difference between the birds and the surrounding air is minimal, heat removal from the birds will be low. By increasing the temperature differential through evaporative cooling and improved insulation, bird heat removal will be increased.

The evaporative cooling system only provides about 20% of the cooling capacity of the broiler, air speed or wind chill effect is by far the greatest contributor to cooling. The faster the air exchange rate, the cooler a house will be. Unfortunately a good air exchange capability alone will not guarantee bird comfort.

Air speed is the most important component in any tunnel house design. The transition ventilation system can be argued as being the most important system in the modern broiler house. It ensures efficient air exchange and temperature management without creating excessive air movement at chick level. Until broilers have full feather development, they are very sensitive to air speed, which impacts feed consumption. Growers in hotter regions often overlook the importance of choosing and installing a high quality inlet.

Price, rather than the long-term impact on early performance, is too often the driver of equipment that represents only about 3% of total capital cost. As stated earlier, remember that for every 1 gram of bodyweight improvement in the first week, we will see an extra 5 grams or more at slaughter.

Static pressure control is essential for ventilation systems in a closed environment house. All new houses should be commissioned only once they pass a simple pressure test. The following is an example of expected pressure readings for a new house with air velocity in the region of 3.5m/s in various positions along the length of the house: The most important design decisions revolve around achieving the genetic potential at lowest operating costs.

Tunnel fan choice is critical and should be based not on unit price but the following:

  1. Energy efficiency – cfm/Watt or mÑ/hr/Watt. A minimum of 21cfm/watt at 25Pa.
  2. Airflow ratio indicates how well the fan holds up under high static pressures. Should be greater than 0.75 All reputable fan suppliers will have their fans tested. In the future energy costs will not decrease.

In summary, the key design decisions in any new project are by far insulation; inlet choice and its installation; the house’s ability to maintain adequate pressure; and the choice of tunnel fan. 

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