This is a summary of the information shared during 10 webinars from the series: 2021 UGA Cold Weather Poultry House Ventilation System Principles, Design, and Operation Seminar. The app Poultry411 was used as the main tool to calculate minimum ventilation rates and house tightness.
Indoor and Outdoor Relative Humidity and Temperature
The outside air acts as a dry sponge, removing the water the birds release into the barn everyday. The minimum ventilation required depends on the current situation (relative humidity and temperature) inside and outside the barn, as well as the amount of water that is consumed by the birds daily.
The relative humidity is the percentage of moisture in the air, and the drier the air, higher will be the ability to reduce moisture inside the barn. Temperature changes the moisture holding capacity of the air and warmer air can hold more moisture. During the winter, the colder air outside brings less moisture with it and has a higher ability to remove the moisture once it heats inside the barn. So, generally during the winter ventilation rates can be reduced 10 to 15%.
The renewal of oxygen in the barn is very easily attained, but if you have production of ammonia in your barn it is hard to eliminate. Ammonia concentration can be reduced in half by doubling the ventilation rate, but it is always better to prevent the production of ammonia before it becomes a problem by adjusting your ventilation frequently and controlling moisture.
There are several charts and tools to calculate the minimum barn ventilation. Poultry411 is a free app, available for IOS and Android that has a calculator for minimum ventilation rate.
Negative Pressure, exhaust fans and air inlets
One of the best ways to ventilate the barn without using too much fuel is using negative pressure ventilation principles. It requires exhaust fans to control the amount of air coming in and air inlets for air mixing and distribution.
When negative pressure is achieved, an open door slam shuts on its own. Negative pressure can be measured with a negative pressure gauge. Ideally, it should range between 0.05” and 0.10” but it needs to be higher in colder weather (0.08”- 0.14”).
It is important to remember that pressure is influenced by the amount of opening of the fan.The greater the amount of opening in the fan the lower the pressure is going to be.
With negative pressure, the air velocity inside the barn is the same regardless of fan and inlet location. This is important because with more control of the air speed you can better adjust the direction of the air. Ideally, we want the cold incoming air to enter close to the ceiling and reach the middle of the barn (where the hot stale air is) so that it can get warmed-up before coming down to the floor.
Air inlets act with the negative pressure to control the direction and the speed of the incoming air. Adjustable sidewall inlets are ideal because it allows the farmers to open them more or less depending on the situation.
Number of inlets open should increase when there is a high density of birds. New, tighter barns also need more inlets because there isn’t enough air exchange coming through the cracks.
We want the inlets to direct the air towards the ceiling with a higher speed so that it reaches the center of the barn without going down to the floor and chilling the birds.
The colder the outside air is, the heavier it is and it tends to fall to the ground faster. In this condition, more exhaust fans should be on to keep the negative pressure high. Also, higher inlet opening will help increase how much further the incoming air travels inside the barn before falling. However, higher inlet opening during cold weather will reduce the temperature in the barn when the fans are on, increase costs with heating and chill the birds. A solution can be to close half the inlets.
House tightness and circulation fans
House tightness has a great influence on heating costs as leaks will allow more cold air to enter. Low house tightness makes it harder to control the conditions inside the barn, generating cold birds and wet litter. You can calculate how tight your barn is by using the app Poultry411 that was mentioned here previously. The app has a calculator that provides an estimate of your house tightness based on static pressure test results.
If your barn isn’t tight, there are some things you can do to improve it. Seal curtains tightly and create a curtain pocket or flap to keep the curtain sealed tight. Seal tunnel and side wall fans that are not being used from the outside and add plastic behind tunnel fan shutters. If you can, inspect side walls for leaks and use spray foam to improve tightness.
In leaky houses, the cold air that enters through the cracks goes to the floor, while the hot and dry air stays stale close to the ceiling. Even in tight houses, circulation fans are helpful to have a better uniformity of temperature and air temperature in the barn. Uniform temperatures allow the birds to spread evenly throughout the barn and circulation fans also create air movement over the litter to remove the moisture.
In order to provide better air circulation and litter drying capacity, circulation fans should run constantly and should mix at least 20% of the volume of the air inside the barn per minute.
Final considerations
It is harder to manage ventilation inside the barn during cold weather. Having a tight barn and establishing a negative pressure helps. Producers should ideally use a maximum of 2 cfm per square foot of minimum ventilation/timer fan capacity. How much the fans are operated depends on humidity. Using many exhaust fans can reduce barn temperature so it is recommended to use fewer fans for a more uniform temperature inside the barn. On the other hand, having several smaller circulation fans towards the center of the barn helps distribute the air better than fewer bigger fans.
There are several tools to help you with your cold weather ventilation. Use the Poultry411 App to calculate minimum ventilation rates and house tightness, use thermal cameras or insect foggers to detect cold air leakage inside your barn. Make sure your temperature sensors are properly placed, they should be 10” from the side walls. Use the tools available to constantly monitor your condition and make adjustments as needed. Proper ventilation will avoid wet litter, ammonia formation and all the subsequent problems like footpad dermatitis that can affect bird welfare and reduce your production.
Reference: Information obtained from the series: 2021 UGA Cold Weather Poultry House Ventilation System Principles, Design, and Operation Seminar
University of Georgia Poultry Housing Tips.
