Hot weather can have a negative impact on turkey performance. When turkeys are exposed to very high temperatures, especially for prolong periods of time, there is potential for increased mortality. At the same time daily weight gain and feed conversion will likely suffer as birds go into survival mode rather than growth mode. This is a drain on the overall energy utilization of the system.
When turkeys begin to pant, the process of energy loss has already started. Therefore, any management techniques that can be implemented to reduce this stress and maintain bird comfort during hot weather will benefit the turkeys and the bottom line. These same techniques can also be a vital component in an animal welfare program which addresses bird comfort. Due to the current (or what seems like the consistent) slow economic state of the turkey industry, we need to evaluate each farm system separately to determine how we will improve the overall hot weather management on the farm. While tunnel ventilation is the most efficient method to cool birds and control the environment during hot weather, we must consider other alternatives if economics dictate this.
Tunnel ventilation has been utilized in the North American broiler industry on a large scale since the 1980’s. In some broiler complexes 100% of broiler facilities have been constructed with or converted to tunnel ventilated systems. This has resulted in sustained improved performance throughout the year and improved bottom line for producers. Tunnel ventilation has gained popularity in commercial turkey production. Many companies in the southern tier of NA have realized the benefits. A lot of northern tier producers are also seeing results. As bird weights increase the need for improved ventilation and bird management has become critical.
Over the past 15 years, typical turkey tom production in North America has seen weights increase from 38 lbs to over 46 lbs at the same age. Hen production has also seen improved weight gains and lower feed conversions (14 lbs in 14 weeks in 1987 to 14 lbs in 11 weeks). Interestingly, this has been done within same floor space per bird resulting in a significant increase pounds per square foot. This additional pressure on turkey facilities requires that producers evaluate their systems to be certain adequate management tools are in place.
Here we are focussing on defining tunnel ventilation for the typical commercial turkey operation. It will compare the basic differences between conventional and tunnel ventilation. Emphasis will be placed on the importance of tunnel management during hot weather conditions.
The following issues influencing bird comfort will be addressed:
- Definition for tunnel ventilation and the importance of maintaining effective cooling temperatures related to the bird’s comfort zone;
- Understanding heat production and its removal from a turkey facility;
- Designing a typical tunnel system and understanding fan efficiency;
- Evaporative cooling in reducing temperature;
- Importance of using environmental controls
Definition for tunnel ventilation and the importance of maintaining effective cooling temperatures related to the bird’s zone comfort
Tunnel ventilation can be defined as a type of ventilation where air enters at one end of a poultry barn and is exhausted by ventilation fans at the other end. The exhaust fans pull air out of the barn, creating a negative pressure as air enters inlets at the opposite end. As with any ventilation system, the goals for tunnel ventilation include removal of excess heat, removal of excess moisture, minimize dust and odours, reducing the build up of harmful gases (such as ammonia and carbon dioxide), and providing sufficient oxygen for efficient respiration. When this is accomplished turkeys are provided an optimal environment for growth and sound animal welfare. The difference (or advantage) of using tunnel ventilation compared to conventional hot weather systems is that air speed creates a wind tunnel that improves effective cooling of birds in the barn through convective heat loss. This wind speed and effective cooling can then be controlled by farm management.
Tunnel ventilation differs from conventional open curtain sided or ‘naturally’ ventilated structures in its ability to maintain this wind tunnel. In a typical conventional barn, curtains are opened to allow natural winds and stir fans to attempt to cool birds during hot weather. Conventional systems are limited by the reliance on natural cross winds and low air speeds from typical circulation or stir fans. These stir fans normally reach air speeds of approximately 100-150 fpm for a short distance directly in front of the fan, allowing for very little cooling effect on large birds. Tunnel ventilation, if designed properly, can provide constant desired air speeds typically ranging as high as 700 fpm. The advantage of this constant wind speed is that it creates a wind-chill over the turkeys so they feel a lower ‘effective temperature’ than the actual ambient air temperature (Donald, 1995). Figure 2 shows that as the air speed increases, wind chill also increases thus lowering the effective temperature that the turkey feels.
It is important to understand how many circulation fans are necessary in a naturally ventilated barn to simulate tunnel ventilation in order to capitalize on wind chill effect across the barn. In most cases the simple calculation can be used to determine what area a fan can cover at acceptable speeds. This formula is 15’ x Diameter’ = width of throw and 5’ x Diameter’= width of throw.
Figure 1 shows the configuration and estimated number barn. It actually takes more fans and electricity in a naturally ventilated barn with adequate stir fans to simulate a tunnel barn at 600 fpm air speed. When air speeds reach as high as 600 fpm the effective temperature that the turkey feels is approximately 15°F less than the 85°F ambient temperature. In a tunnel ventilated barn, this wind tunnel or wall of air is relatively consistent from end to end and side wall to side wall (there is some reduction in air speed along the walls due to friction from building materials). This wind tunnel is also very effective at removing radiant heat that birds produce during hot weather. This effective reduction in temperature (wind-chill) is extremely important in maintaining bird comfort. According to information published by the North Carolina State University (Anderson and Carter, 1993), poultry performance is negatively impacted when the temperature rises over 27°C (80°F). Table 1 demonstrates what occurs in a poultry barn as the temperature rises inside the facility.
Reducing the effective air temperature with wind speeds created in a tunnel-ventilated barn enables producers to maintain temperatures within the bird’s comfort zone. Evaporative cooling techniques employed in conjunction with wind speed can further improve the temperature reduction ability in a turkey barn, and will be discussed in more detail later. Not only will turkeys stay alive during extreme conditions, but also tunnel ventilation will help them sustain body weight gain and feed conversion. Tunnel ventilation also keeps the production system efficient by allowing producers to maintain cool weather stocking densities during hot weather. Table 2 illustrates an example of performance data from turkeys raised in tunnel ventilated turkey barns compared with turkeys raised in naturally ventilated barns during the summer months in the Midwest.
This performance data demonstrates the possibility of improved weight gains and feed conversion when turkeys are raised in temperatures within their comfort zone during hot weather. Figure 2 illustrates what happens to the breast meat yield as a relationship to average body weight.
Understanding heat production and removal in a turkey facility
One of the primary goals of tunnel ventilation is to remove heat away from the birds and get it out of the barn. Understanding where this heat originates can be helpful. Many producers may look at increasing insulation values in ceilings and walls to keep heat out of the barn. While insulation is an important factor for conserving heat in the winter, it is not as important as removing the heat produced by the birds during the summer months. Table 3 shows the approximate heat balance of a typical 30,000 ft² finisher barn holding 8,500 toms weighing approximately 40 lbs (18,5 kg).Clearly it is more important to remove the heat from the turkeys than to try to reduce heat entering the building structure from the outside. Sizing the ventilation system properly, including fans and inlets, is necessary to remove the heat production and to provide the air speed necessary to create reduced effective temperatures.
Fan selection is critical when designing a tunnel ventilation system. Static pressure (Pascals), fan shutters, and building structure all affect the efficiency of the fan. In the North American market, most fans have been tested by the Air Movement and Control Association (AMCA) and test results can also be found on the Bess Labs web site at www.bess.illinois.edu. This information will allow producers to make sound decisions relative to the power each fan will provide under different loads as well as how efficient they will be relative to utility demand. Choosing a fan based on price and ventilation capacity alone can cost money in the long run.
Designing a typical tunnel system
A common tunnel ventilation design allows for a complete air exchange in one minute. So for a 600 ft long barn, approximately 600 fpm will be necessary. A typical method for calculating the fan capacity needed is to consider the cross-sectional area of the barn. Therefore, a simple calculation taking the cross sectional area and multiplying it by the desired air speed will result in the total fan capacity needed. For a typical North American barn that is 50 ft wide with an average ceiling height of 12 ft and a desired air speed of 600 fpm, the result is a fan capacity of 360,000 cfm.
The inlet capacity must be enough to fulfil the needs of the exhaust fans without creating too much pressure so as to restrict the fan capacity. It is necessary to have enough inlet capacity to allow the air to enter the barn at approximately 4” of water column (statistic pressure). In order to do this, a simple calculation can be made by dividing the cfm capacity by 525 fpm, which is the approximate air speed for this static pressure without cool pads. The result will be the total inlet opening for the necessary fan capacity. If cool pads are used, the incoming pressure will be approximately 0.06” static pressure, so a 375 fpm should be used as the divisor to get a larger opening due to restrictions.
In barns that may have open trusses with high ceilings, it is common to place baffles approximately every 30-40 ft that covers the exposed truss. This type of system, in effect, lowers the ceiling by forcing air to travel below these restrictions and must be accounted for when calculating average ceiling height for fan and inlet capacity. So, a barn with a peak of 18 ft and 9 ft sidewalls can reduce the average height from 13.5 ft to as low as 8 ft by using baffles. This will reduce the overall fan capacity necessary to maintain the desired air speed. Keep in mind, however, that the baffles will create a restriction to airflow and therefore more static pressure in the barn which reduces the efficiency of the fans. For this reason, a smooth ceiling surface is preferred.
Evaporative cooling in reducing temperature
Evaporative cooling can be an effective method to reduce the temperature of incoming air. This method is most effective when relative humidity levels are below 80%. In some cases, depending on temperature and humidity levels, air temperatures can be reduced as much as 10°F or more. This reduction in actual temperature, in combination with high air speeds (lower effective temperatures), can take a 90°F room temperature and make turkeys feel like it is 70°F, well within the bird’s zone comfort. Evaporative cooling can be accomplished with cool cell pads, high pressure fogging, or sprinkler systems. Cool cell pads, typically 6 inch thickness, are mounted at the tunnel inlet end and water is slowly sprayed or trickled over the wet pads to cool the incoming air. While this system may be the most effective method to lower temperatures, it is also the most expensive and usually the most difficult to maintain. Also, in most commercial turkey production systems, cool cell pads are only used for a short period during the hottest time of the year, making them even less cost effective.
High pressure fogging is also used to evaporate water into the air lowering temperature. High-pressure pumps running at 200 psi are used to push water though nozzles rated at 1 gallon per minute to create a fine mist. Nozzle lines are normally placed over each tunnel inlet as well within a line strategically placed, depending on tunnel or natural ventilation. Sprinkler systems are similar to high-pressure foggers, but use a larger droplet of water for evaporation. High air speeds are critical for making foggers and sprinklers effectively in hot weather. The amount of water added should be regulated in stages –on hot days and low humidity all nozzles should be used for cooling and on cooler days one-half the nozzles should be used. Thus this system is generally set up with two alternating delivery lines so that intermittent cooling can be accomplished along the length of the barn for uniformity.
Evaporative cooling is effective when the temperatures are over 80°F and humidity levels are below 80% (Poultry Housing Tips, The University of Georgia, Vol.12, No.9). Evaporative cooling is detrimental when humidity and temperature levels are both over this mark, as turkeys can no longer lose heat through respiration. Overuse of evaporative cooling can cause high humidity levels in turkey barns causing wet litter and dangerous humidity levels if not monitored properly.
Importance of using environmental controls
Environmental controls can be useful tools to maintain an optimum environment when tunnel ventilating turkey barns. There are many good controllers on the market that have the ability to control tunnel fans, inlets, and evaporative cooling in stages so that the environment can be regulated slowly. It is important to remember the effect of air speed and evaporative cooling on turkeys so that younger birds that may not be fully feathered are not chilled too quickly. Chilling birds can result in making them sit down, not getting up to eat and drink, which can result in negative performance. At the same time, not using tunnel fans early enough on older turkeys can result in losing the performance advantages of tunnel ventilation. Many commercial producers make the mistake of delaying tunnel implementation until ambient air temperature reaches 80-90°F. By this time birds are already panting, negating any early advantages of tunnel ventilation. Table 4 is an illustration of a typical controller set up for tunnel ventilation.
From the Proceedings of the Midwest Poultry Federation Convention