Controlled Climate Systems with Tunnel Ventilation to Prevent Animal Heat Stress
Tunnel ventilation has been used primarily by Southern poultry farmers in the US to reduce bird heat stress during hot summer days. In the ’80s it was introduced and employed in US Midwestern livestock production facilities and in the past 15 years, the practice has grown popularity for both Poultry & Swine Industries here in Asia. While the benefits and limitations of such systems tinder different weather conditions remain to be fully evaluated, a basic comprehension of how the systems works is helpful.
The structural layout of tunnel ventilated buildings is very simple. Compared to conventional cross-ventilation where exhaust fans are mounted in side walls, the exhaust fans in tunnel ventilation are placed at one end of the building, and air is brought in from the opposite end of the building. (see figure i). Consequently, air travels in a tunnel ventilation system through a much smaller cross-sectional area of the building, and ideally the building should have a low ceiling, narrow width but long enough, ( length of the bldg. should not be < 6x the width, or not > 10x the width ) that should provide a tunnel like effect when passing air from the front to the rear, and produces a much higher air velocity above animal level. From experience We have verified that air velocity is practically nil or zero from the floor up to the animal’s height.
Improving animal heat loss during hot weather
Animals dissipate their metabolic body heat to maintain their constant body temperature. There are four ways by which animals may lose body heat.
• Radiation – the exchange of heat by non contact with surrounding surfaces.
• Convection – the exchange of heat thru the surrounding air.
• Conduction – the exchange of heat by direct contact with another sur face.
• Evaporation – the exchange of heat by evaporating moisture to the ambient air.
• Conductive and radiant heat losses are facilitated by surface temperature differences between the animal and its surroundings, therefore heat loss through theses 2 meth ods may be limited when temperature differences are small. This case may be true in a well insulated animal barn, where heat exchange from animals to their environs is restricted.
On the other hand, heat loss by convection is influenced by temperature difference between animals (Pigs or Poultry) and the surrounding air, and also by the air velocity inside the animal building. A higher or faster air velocity results to faster heat extraction from animals along the airflow path which should pass through the building in a sweeping manner from the front to the rear end, producing a better cooling effect.
An efficient Tunnel ventilation design should keep an appropriate air velocity that can increase heat loss by convection during the warmer time of the day.
Improved animal heat loss by tunnel ventilation will result to numerous benefits:
Improved feed intake, animals eat more when room temperature within their comfort temp range.
• Better daily weight gain.
• Better feed conversion.
• Better milk or egg production.
• Reduced mortality from heat stress higher stocking density.
The cooling effect of moving air by tunnel ventilation is best expressed by observing Felt temperature on the animals.
This is the actual temperature being experienced by the animals inside the building.
Such cooling effect may vary however according to animal type and age, different animals requires a particular environmental conditions from day i to their adult age, this climatic requirement must be addressed carefully. A specific tunnel ventilation design must be applied for every building, and several factors must be considered :
• animal type & age
• building design
• farm site location and climate
Air exchange, air velocity and air temperature are parameters that should be carefully considered when designing for a tunnel ventilation system. It is also important to note that air velocity is derived by deciding on a particular air exchange rate that is applied against the length of the animal building.
Imagine a building which is 60 meters long from front to rear, if air is passed thru the entire length of the building with a velocity of 1 meter per second, the resultant air exchange rate is : 1 complete air exchange for every 60 seconds.
Controlled climate systems
Here in the Philippines, from our experience of almost 15 years in designing Tunnel Ventilation systems, the Ideal Air Exchange Rate for buildings with grown up animals is 1 complete air exchange every 40 seconds, and Felt temperature should go from 25deg – 28deg Centigrade.
Air velocity must be maintained at a certain speed only, when too fast, reduction in felt temperature becomes insignificant, when it gets too slow, it negates the cooling benefit the system generates and causes temperature gaps between both ends of the building, furthermore it pulls down the cooling efficiency of the system.
Air temperature set points are assigned according to animal type and age.
With the use of simple climate computers aided by temperature sensors, temperature inside an animal building is maintained according to its design, with the help of the climate computer that turns on and shuts-off fans according to the programmed set points.
Exhaust Fans ( 50 inch or 36inch dia. ) together with the pumps that facilitates wetting of the cooling pads are controlled by climate computers that renders the system fully automated.
While Tunnel Ventilation can work effectively in extracting heat from animal buildings. during warm weather it also has its own limitations. Tunnel Ventilation alone loses its cooling efficiency when the temperature rises above 32 degrees centigrade.
Beyond 32 degrees C, the Tunnel Ventilation system has to operate together with an evaporative cooling system to be able to effectively extract heat and reduce temperature inside the building.
From the early 1990s when tunnel ventilation was first adapted and tried in the Philippine livestock industry, much has been learned and accomplished, but from where We stand now and with the level of technology that We have on hand, there are certain areas where We can still improve.