Barn Ventilation Theory

Barn Ventilation Theory


4. Types of Ventilation Systems


There are many different types of ventilation systems. This section will introduce you to the two main types of ventilation systems as well as a number of add-ons that can improve the performance of an existing ventilation system. The first system we will discuss is the negative pressure system.


A. Negative Pressure Ventilation System


A very popular choice for a ventilation system is the negative pressure or exhaust cross flow ventilation system. This simply means negative pressure or vacuum is created in the barn when the fans exhaust air. This vacuum sucks fresh air through the inlets into the barn. The air travels along the ceiling, mixes with the stale air and then drops to the animal before being removed from the barn by the fans. This system is very good at accomplishing the five functions of a ventilation system. The next system that can be used in your barn is a variation of the negative pressure system.


B. Chimney Ventilation System


A chimney ventilation system operates using the same principles as the negative pressure system above but instead of wall fans, chimney fans are used. The stale air is sucked up the chimney and then removed from the barn. The major benefit of using a chimney ventilation system is that it tends to be more efficient than a wall fan system. Next we will discuss the ventilation system that offers a different approach to accomplishing our five goals.


C. Natural Ventilation System


A natural ventilation system moves large volumes of air very slowly, creating a quiet, pleasant atmosphere in the barn. Natural ventilation can be adversely affected by large structures such as barns, silos and trees so careful planning is required before implementing this type of ventilation system. The main component of a natural ventilation system are the curtains, which can be raised and lowered to allow fresh air into the barn. The curtains function as very large inlets. The next ventilation system is always used in conjunction with a negative pressure or natural ventilation system.


D. Tunnel Ventilation System


Tunnel ventilation systems are a summertime addition to an existing ventilation system such as a negative pressure or natural ventilation system. During the hot times of a warm day the tunnel ventilation system will attempt to move the air around the animal at very high speeds, creating a draft. This makes the animal cooler than the outside temperature.


Note: Tunnel ventilation should not be attempted if the outside temperature is higher than the animals body temperature. Doing so can cause the animal to be very uncomfortable and in severe cases your livestock could die. The next system makes an excellent addition to either a negative pressure or natural ventilation system.


E. Recirculation System


Recirculation ventilation systems are also only used as an addition to an existing ventilation system. Recirculation in the winter months can assist with the mixing of air throughout the barn. During the summer recirculation can be used to create a draft condition, which may increase the comfort of the animal in the summer heat. If you live in a low humidity area the next system can also be used to decrease the relative temperature in your barn.


F. Evaporative Cooling System


As water evaporates, and changes from a liquid to a gas heat is absorbed. This process can be used to cool a barn. The disadvantage of this system is that it increases the humidity within the barn. If you live in an area which already has high humidity (80% or greater) then this method is not for you.


However if you live in an area with low humidity, then an evaporative cooling system could be used to lower the effective temperature in your barn. The last system add-on we will discuss is used in barns with manure pits.


G. Pit Ventilation System


Manure creates a number of gases during decomposition. The lighter gases created include ammonia and methane. These gases will rise and be removed from the barn by the fans during the normal air exchange cycle.


However there are heavier gases created such as hydrogen sulphide and carbon dioxide that can linger in the pit. The purpose of a pit ventilation system is to remove these heavy gases from the manure pit.