Curtain-sided houses rely extensively on natural air movement. These houses work best when they are located away from obstructions such as other buildings or trees that can block natural air currents. To avoid total reliance on natural air movement, most producers have added circulation fans in curtain houses to increase air movement and promote the loss of body heat from the birds. These fans should be spaced and positioned to maintain air movement between fans and to direct their flow in a way that will increase the turbulent air movement around the birds. Spacing of the fans depends somewhat on their size, but they are generally spaced about 25 to 30 feet apart in curtain layer houses and 40 to 50 feet apart in broiler houses.
Circulation fans should be controlled by thermostats set at about 85° F (or lower in hot weather). To save energy, the fans should shut off when the temperature drops below 85° F except during periods of extended hot weather. At those times, it is advantageous to leave the circulation fans running through the cool evening hours by turning the thermostats down to 75° F or even lower. This practice will lower the inside temperature faster, providing the birds with a cooler environment in which to dissipate stored body heat.
Foggers reduce air temperature in the house on hot days (90° to 95° F) when humidity is low, especially during midday when humidity levels are lowest and temperature is highest. The foggers inject fine water particles into the warm inside air. As the water vaporizes, heat is absorbed from the air, lowering its effective temperature. When foggers are used, they should be operated intermittently or designed to avoid excessive water flow into the environment.
If too much water flows through the foggers, humidity levels may increase to the point where birds can no longer cool themselves by evaporation. In addition, litter made wet by excessive fogging can lead to performance and health problems. The appropriate water flow rate and timer settings depend on the method of ventilation, ventilation rate, bird size, and outdoor conditions. Fogging systems in naturally ventilated house are typically designed for a water flow rate of 50 to 100 gallons per hour.
In forced ventilation systems, all air movement is produced by fans in the building walls. Houses that use this type of ventilation are also referred to as controlled environment systems. Power ventilation houses can provide good, uniform airflow patterns under hot summer conditions if correct static pressure is maintained and airflow obstructions are avoided. It is very important to determine how much air should be moved through the building.
This can be accomplished in two ways. Approximate values for the minimum volume of air required per pound of poultry body weight are given in Table 3. These values can be used to determine the total fan capacity required for the house. Keep in mind, however, that the rates shown are minimum estimates, and it is best to plan for the worst possible case. For example, the efficiency of fans is greatly reduced if they are allowed to become excessively dirty, reducing the airflow through the building.
Table 3. Recommended Minimum Ventilation Rates Based on Body Weight
Body Weight (pounds) = Airflow Per Pound of Body Weight (cubic feet per minute)
- 1 to 6 = 1.0
- 6 to 15 = 0.8
- 15 to 30 = 0.7
A second method for determining airflow rate is to plan for a summer ventilation rate of one complete air exchange per minute. The necessary airflow volume per minute is equal to the interior volume of the house, which can be calculated from building measurements.
A new arrangement for ventilating poultry houses in the summer is tunnel ventilation. Simply put, this method involves moving air along the building axis from inlets to exhaust fans, providing high airflow velocities. This rapid air movement increases convective heat loss, reducing the effective temperature experienced by the birds. Figure 2 shows the effective temperature (wind chill) that the bird feels at a given air temperature and velocity. Most of the benefits of tunnel ventilation occur at an air velocity of 350 feet per minute. This velocity should be considered the minimum for most house designs. Tunnel ventilation systems do not operate on a static pressure difference. In fact, they work best when there is no pressure difference between the inlets and the fans.
Evaporative Cooling with Power Ventilation
Fogging nozzles and evaporative cooling pads are options that can be used in combination with power ventilation systems and especially with tunnel ventilation. Evaporative cooling uses heat from the air to vaporize water, increasing humidity but lowering air temperatures. Evaporative cooling can be effective in North Carolina during the hottest part of most days because that is when humidity is lowest. On rare occasions the humidity remains high the entire day or immediately before or after a storm; evaporative cooling is ineffective under such conditions and should not be used.
Evaporative cooling pads operate on the same cooling principle as foggers, except that the air is cooled when it passes through the wet pads as it enters the house. This method avoids the problem of wet litter sometimes encountered with foggers, allowing evaporative cooling pads to be used on a continuous basis. Aspen fiber and corrugated cellulose are two materials widely used as cooling pads. Regular maintenance is necessary to ensure long life of the pads. First, the pads must be allowed to dry out once each day. They can be dried by turning off the water supply but allowing the fans to continue running.
The best time to dry the pads is in the early morning hours when the outside temperature is relatively low. Drying allows the adhesive that holds the pad together to maintain its integrity and also helps reduce the buildup of algae. To further reduce the growth of algae, an algicide can be used in the water supplied to the cooling pads. Calcium hypochlorite, ethylene dichloride, or ammonium chloride can be administered at a rate of 6 ounces per thousand gallons of water, applied once each week. In addition, the pads should be washed monthly to remove dust and sediment. The entire system should be flushed monthly to remove the mineral salts and dirt that accumulate in the pipes and reservoir.
Evaporative pads constructed of aspen or cellulose ranging in thickness from 2 to 6 inches are being used in the industry in conjunction with power ventilation systems. On a hot, dry day these pads evaporate water at a rate up to 100 gallons per minute per hundred square feet of pad surface area. Using tunnel ventilation, they can evaporate up to 200 gallons per minute per hundred square feet of pad on a hot, dry day.
Fogging systems have also been used successfully in environmentally controlled poultry houses. Fogging systems that provide a reliable fine mist and that have water filters (to keep nozzles from clogging) and also have a positive shutoff to prevent dripping can provide successful cooling without causing wet litter. The water pressure should be at least 100 pounds per square inch (psi) to achieve a fine mist; a pressure 200 psi is preferred. The volume of water that goes through the fogging system and the number and placement of the nozzles are critical design considerations. A total flow rate of up to 1 gallon per hour per thousand cubic feet per minute (cfm) of ventilation can be used in tunnel-ventilated houses.
The design of the fogging system is critical for tunnel-ventilated houses. Cross lines of nozzles that provide a “curtain” of fog across the house at various intervals are fairly effective. Nozzles or lines of nozzles should be located close together near the air inlets, then spaced farther apart along the house, ending 60 feet from the exhaust fans. Tunnel-ventilated houses can use substantially more fogging capacity (50 to 100 percent more) than naturally ventilated houses because the forced air movement is able to carry the mist.
source: ces.ncsu.edu, aces.edu