Evaporative cooling has become a common feature of ventilation systems for barns and livestock facilities. Evaporative cooling aids ventilation by circulating cool air over the livestock, lowering the ambient temperature during periods of high heat, and alleviating the effects of heat stress. Evaporative cooling is often incorporated into tunnel ventilation systems, but few farmers are aware of the benefits a freestanding evaporative cooler can provide, both in terms of cost and cooling power. These are high powered units, capable of moving and cooling large amounts of air. When combined with well-constructed, natural ventilation system,evaporative coolers provide effective relief for cows, pigs, chickens, or any number of livestock housed in large enclosures.
Natural Ventilation Systems
Natural ventilation is a passive method of air exchange that utilizes functional structural openings in order to encourage air movement through barns. Natural ventilation is popular because it's a low cost approach that is extremely effective under the right conditions. Natural ventilation relies on four key principles of design.
|Good Construction||Barns designed for natural ventilation should be constructed on high ground, unobstructed and perpendicular to the prevailing winds. Support structures such as silos should be constructed on the leeward side of the barn. There should be no leaks and cracks to dilute air flow|
|Air Exchange||Direct air flow routes encourage smooth air flow through a structure and prevent air from lingering and becoming stagnant. Air flow must be continuous to be effective, even during low temperature conditions|
|Flexibility||The ability to adjust air flow in response to wind conditions. Provided by multiple doors and ventilation points, such as: |
|Control||The ability to alter rates of air exchange depending on temperature conditions. The rates of exchange are: |
Though natural ventilation systems are effective at removing moisture and heat, they're limited by environmental conditions. Periods of low wind reduce its effectiveness, which is why natural ventilation systems are often augmented by mechanical devices in order to spur air circulation.
Evaporative Coolers & Natural Ventilation Systems
Evaporative coolers such as the Portacool PAC2K482S, the Aercool MB36, or the Luma Comfort EC220W enhance the effectiveness of natural ventilation systems. By design, they use high-powered fans to move large volumes of air and generate cooling. A pump draws water up from a storage tank and spreads it over a specially constructed cooling pad, located in front of the fan blades. The fan blows air through the pad as the water soaks into it. Water is a natural heat absorber. As the air moves through the pad, its latent heat is transferred to the water molecules inside the pad. The water evaporates into vapor and cool, clean air is blown out into the surrounding environment.
The area affected depends on the size and power of the unit in question. The largest evaporative coolers can cover anywhere from 1000 - 4000 square feet and lower the ambient temperature anywhere from 15 - 20 degrees. When placed in front of open doors and ventilation points, evaporative air coolers move cold air rapidly through a structure. The fans push the stale air out through the opposing sidewalls or endwalls, creating negative air pressure inside the building that draws fresh air in. The air movement allows livestock to discharge heat through sweat, while the cool air from the cooler reduces the ambient air temperature. They are especially useful during periods of high heat and low wind, conditions unfavorable to natural ventilation systems, when it is difficult to create high rates of air exchange.
The primary advantage of natural ventilation and evaporative cooling systems is they allow you to control temperature and air flow at an extremely low cost. Portable evaporative coolers designed for agricultural use have a CFM (cubic feet per minute) rating of 1650 - 20,000 and consume only 220 - 1600 watts per hour. The higher the CFM/watt ratio, the less electricity it takes to move the air. Because evaporative coolers are compact, self-contained units with only two working parts - the water pump and fan motor - they consume very little power. Depending on the size of the units, the cost for one hour of operation is $0.02-$0.10. Average yearly costs are $60 - $325, compared to over $3000 per year for a tunnel ventilation system.
Evaporative coolers provide savings in terms of set-up and maintenance. Unlike sprinkler or fogging systems, which use an intricate systems of pipes, mister, and high-powered fans, evaporative coolers require little set up. They arrive fully assembled and require only a power connection and water supply to being operating. Primary maintenance consists of removing and cleaning the cooling pad in clean water, draining excess water from the unit, and vacuuming out any residual dirt from the sump tank.
Effect on Heat Stress
Ventilation is an absolute necessity for both barns and livestock. Poorly ventilated barns trap heat and moisture, which negatively impacts the building's structural integrity and the health, lifespan, and productivity of the animals inside. Excessive moisture often condenses on walls and ceilings, where it can ruin wood and metal fixtures, damage insulation, drip down into feed containers. Excess heat leads to heat stress, effects of which include decreased appetite, weight loss, reduction in egg and milk production, and even death. The combination of heat and moisture also contributes to respiratory sickness, bacterial formation, and fungal growth in cows, pigs, and chickens.
Because all forms of livestock generate heat and moisture through digestion and respiration, excessive heat is always more of danger in an enclosed facility than excessive cold. Freestanding evaporative coolers alleviate this concern by delivering a constant stream of cold air. Evaporative coolers are portable, and can be positioned or re-positioned to take advantage of prevailing winds or provide relief to trouble spots. Evaporation is a powerful cooling mechanism. Under the right conditions, it can reduce ambient temperatures dramatically by as much as 20-30 degrees.
Effect on Cold Stress
Evaporative coolers offer a flexible solution for cooling and circulation problems. During cold periods, when reducing internal temperatures is no longer a concern, the cooling function can be deactivated. This stops the water pump, but allows the fan to continue functioning and circulating the air.
Because humidity inhibits evaporation, evaporative coolers are most effective in areas with a relative humidity level below 60 percent. Relative humidity is the ratio between the amount of water vapor in the air and the maximum amount of vapor the air can hold before it starts condensing back into water. When humidity is low, the air's capacity to store water is high and evaporation occurs quickly. As the air becomes saturated, evaporation decelerates, which diminishes an evaporative cooler's ability to reduce temperatures.
Because they cool through evaporation, evaporative coolers also emit water vapor and should never be used in enclosed environments. This not only prevents effective operation, it also contributes to heat stress by raising the humidity level in the environment. Always place them in well-ventilated areas, where the humidity they generate can be expelled and dry air drawn in to facilitate cooling.
The combination of evaporative coolers and natural ventilation provide an excellent environment for all breeds of livestock. The beneficial features of each system complement one another almost perfectly. Incorporating cold air, strong air flow, and rapid circulation, the deliver a powerful cooling solution that ensures your animals remain comfortable and productive.