Minimum Ventilation in Cool Seasons
Cool weather demands different strategies and systems compared to summer ventilation. In cool months, “Minimum Ventilation” settings are intended to remove moisture and ammonia from the house. To be effective minimum ventilation requires adequate insulation of houses, functional inlets and controls and selection of fan settings to keep the environment in the chicken house as evenly conditioned as possible.
Hens drink 5 gallons per 100 per day, approximately twice the amount as daily feed intake at moderate temperature. As ambient values rise above 90F, water intake may treble to allow for cooling by loss of latent heat and by evaporation from the respiratory tract. In a layer house with 200,000 birds, cumulative water consumption will amount to10,000 gallons per day.
Of the water consumed, approximately 75 percent is excreted into manure which is either held in a pit or deposited on belts. Moisture is either exhausted by extraction fans in pits or dried on belts by directed streams of air. Moisture from manure evaporates into the air of the house. In addition water is voided by the flock during respiration. The ventilation system must remove this moisture efficiently in order to reduce the liberation of ammonia produced by bacteria in manure. High levels of atmospheric ammonia (above 25 ppm for more than four hours each day) will irritate the respiratory tract, exacerbate vaccine reactions and increase the severity of respiratory infections.
Unfortunately, it is not adequate to simply turn on additional exhaust fans or to adjust the fan timers to reduce moisture in manure. It is critical that fresh air should be “conditioned” and evenly distributed over the entire flock. Stratification from floor to ceiling, longitudinal temperature gradients in the house and “dead spots” along walls result in uneven distribution of the flock which creates problems of local high stocking density.
Current Minimum Ventilation Solutions – An Opportunity for Improvement
The most common minimum ventilation systems rely on exhaust fans activated by timers that vary the duration of the operating cycle based on temperature sensors in the house. Sidewall or ceiling inlets are opened when the fans run to allow fresh outside air to be metered into the building. Fans are generally run at a high static pressure during minimum ventilation to create high air speed at the inlet. This is necessary to condition the incoming cold air stream by mixing with the warmer air in the house before contact with the flock. Without the high static pressure, the heavier cold air entering through sidewall inlets would sink to the floor and over the birds without having been conditioned.
Problems with current minimum ventilation solutions include:-
• Air speeds decrease very quickly beyond the inlet as determined by the inverse square law. In modern wide houses, fresh air may not reach the center of the house before it slows and falls to the floor.
• Because fans must run against a high static pressure, they operate less efficiently and consume more electricity per volume of air exhausted in a given cycle of operation.
• Supplemental heat, when needed, is added at specific locations so temperature gradients develop within the house, affecting the distribution of the flock and the moisture content of litter.
• Temperature stratification occurs naturally because warm air is less dense than cold air and rises to the ceiling – it is not uncommon for the temperature to rise by 1 to 3 degrees per foot above the surface of the litter!
• As exhaust fans cycle on and off, the movement of fresh air from inlets is interrupted. This prevents constant mixing of air necessary for a uniform atmosphere and an even distribution of heat.
• As a result of inadequate mixing of cool outside air with warmer inside air, condensation can form on walls, fans, curtains and other surfaces, resulting in deterioration of equipment and structural components of the house.
Engineering the Ideal Cool Season Ventilation System
A new system for cool-season ventilation has been designed by VAL-CO® using a centrifugal fan with an optional metered ceiling inlet. The system, known as the VAL-CO® Hemisphere Mixing Fan, features a large diameter (48” or 72”) rotor with radial paddles housed in a steel frame and mounted to the ceiling of poultry houses.
In common with all centrifugal fans, the VAL-CO® Hemisphere Fan draws air from the center of the rotor and propels it outwards. This action entrains air from below to provide vertical mixing and distributes air evenly throughout a house. When combined with the optional metered ceiling inlet, fresh cool outside air is simultaneously drawn from above and mixed with the warm air near the ceiling.
The VAL-CO® Hemisphere Fan prevents drafts by slowly circulating air in all directions. Because the VAL-CO® Hemisphere Fan has a large diameter with centrifugal movement it moves a large volume of air at slow speed. Users report less than two degrees of temperature difference from litter to ceiling and from end-to-end throughout the house.
The gentle air movement created by the VAL-CO® Hemisphere Fan extends up to 75 feet in all directions. Recommended spacing is 75 to 125 feet in a single row down the middle of the house.
When used with the optional metered ceiling intake, there is no need for exhaust fans to run at high static pressure, as the VAL-CO® Hemisphere Fan is consistently mixing house air obviating the need for high air velocity at the inlets. Lower static pressure means higher efficiency of operation and longer life of fan motors.
When exhaust fans shut off, the VAL-CO® Hemisphere Fan continues to run, providing consistent and gentle air movement. This results in a consistent and comfortable environment for the flock with dry litter, lower ammonia and less condensation.
The Bottom Line
The innovative design of the VAL-CO® Hemisphere Fan is compatible with retrofitting to existing houses or as a component of a new installation. The VAL-CO® Hemisphere Fan dramatically reduces temperature variations and improves bird comfort and hence egg production, case weight and feed conversion efficiency.