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Plastic Evaporative Cooling Pads

Plastic Evaporative Cooling Pads...A First Look

Published: August 30, 2012
By: Dr. Mike Czarick and Dr. Brian D. Fairchild (University of Georgia)
Figure 1. Evaporative cooling system with plastic pads.
Plastic Evaporative Cooling Pads...A First Look - Image 1
Little has changed when it comes to poultry house evaporative cooling pads over the last 30 years. Yes, there have been some relatively minor changes in things such as flute angles (45° X 15° vs. 30° X 30°), edge coatings, and pad thickness (6" vs. 4"), but for the most part the traditional paper pad looks and cools about the same as it did decades ago. Recently, there has been interest in a very different type of evaporative cooing pad, one constructed of plastic. It is hoped by many that a plastic pad would have a longer life, be easier to clean/sanitize, and be more tolerant of poor water quality than paper pads. Though the idea of a plastic evaporative cooling pad may sound appealing, it is important to realize there are very good reasons why we have traditionally used paper evaporative cooling pads.
Though it may not look like it, significant engineering has gone into the design and construction of the modern paper evaporative cooling pad. Pad flute size must be designed not only to maximize the cooling of the incoming air, but to minimize the resistance to air flow thus maximizing the performance of the tunnel fans. It is a delicate balancing act. The smaller the flute size, the greater the cooling, but the greater the resistance to air flow, and the more likely the pad will become clogged by dirt, algae, or even by the water circulating over the pad. The flute angles must also be designed to ensure that the water flows over the pad in such a way that the pad flutes and surfaces remain as clean as possible so as to maximize wind speed produced by the tunnel fans. By far the trickiest part of designing a quality paper pad is engineering the paper itself. Evaporative cooling pad paper is infused with resins and cured in such a way that it is not only rigid and long lasting, but "soft" and porous enough to allow water to easily wick throughout the entire pad. The wicking action is crucial when it comes to maximizing the cooling produced by a pad. First, it minimizes the likelihood of dry spots. Secondly, the wicking action of a paper pad allows it to absorb and hold a substantial amount of water. In fact, the typical one foot section of a five-foot-tall paper evaporative cooling pad can hold 0.6 gallons of water. This means that after the pad system circulation pump shuts off, a quality paper pad can continue to produce the same amount of cooling for 10 to 15 minutes and will continue to produce some level of cooling for up to 30 minutes.
Though plastic evaporative cooling pads are similar to traditional paper pads, there are significant differences. One of the most notable differences is that instead of being constructed with alternating straight path flutes/channels, plastic pads have alternating curved or "U" shaped flutes. There are small holes in the flutes that both help to increase the surface area of the pad as well as facilitate the flow of water throughout the pad. This is a key challenge with a plastic evaporative cooling pad. With a traditional paper pad, the wicking action of the paper often means that water doesn't have to be directly delivered to every square inch of a pad. A single stream of water flowing through a pad can wet a few inches of pad on either side of the stream. The same cannot be said of a plastic pad. To ensure that the entire pad stays wet the water flow through the pad system has to be significantly greater than that typically required with a paper pad so that the entire pad is thoroughly wetted.
Figure 2. Examples of plastic evaporative cooling pad
Plastic Evaporative Cooling Pads...A First Look - Image 2
To better understand the differences between plastic and paper pads, a study is currently being conducted using a plastic pad that has been installed in a number of poultry houses overseas as well as swine houses here in the US (Big Dutchman PP150-3 http://www.bigdutchmanusa.com/environment/environment/cooling/rainmaker.html). The traditional paper pads on a 40' X 500' tunnel-ventilated broiler house in North Georgia were replaced with plastic pads in June of 2011. The five-foot-tall, 6" thick plastic pad is manufactured in two-foot sections and fits in most conventional paper pad evaporative cooling systems. Furthermore, since the pad was designed to have the similar air flow/static pressure characteristics of traditional paper pads, pad area requirements are the same for a house with the plastic pad as they are for a house with traditional six-inch paper pads. To help evenly distribute water along the top of the pad, a two inch thick paper distribution pad was placed on the top of the pad (green pad at the top of the black pad in Figure 1).
As expected, the plastic pad produced less cooling of the incoming air as compared to the paper pad (Figures 1,2, and 3). The difference in cooling was a function of outside temperature. In the morning or on days when the outside temperature was in the eighties, the paper pad tended to produce one to two degrees more cooling than the plastic pad system (i.e. 8°F vs 6°F cooling). But, as outside temperature increased and relative humidity decreased, the difference in cooling produced by the two systems increased. During one particularly hot week, when outside temperature approached 100°F, the plastic pad system produce approximately five degrees less cooling than the paper pad system (i.e. 14°F vs. 19°F).
Figure 3. Inside/Outside house temperatures (plastic and paper pads)
Plastic Evaporative Cooling Pads...A First Look - Image 3
Figure 4. Inside/Outside house temperatures and Rh (plastic and paper pads)
Plastic Evaporative Cooling Pads...A First Look - Image 4
Figure 5. Cooling produced by paper and plastic pads as a function of outside temperature
Plastic Evaporative Cooling Pads...A First Look - Image 5
Figure 6. Incoming air temperatures in houses with plastic and paper evaporative cooling systems
Plastic Evaporative Cooling Pads...A First Look - Image 6
It is important to realize that the reduction in "evaporative cooling" does not always result in a substantial reduction in "bird cooling." During hot weather we use evaporative cooling to lower our house temperatures to increase the transfer of heat from the birds to the air (sensible heat loss). The downside is that this cooling comes at a cost, increased humidity. For every 1°F of cooling produced through the evaporation of water the relative humidity of the air in a house will increase approximately 2.5%. Though the air temperature is lower, the increase in the relative humidity reduces the bird's ability to cool itself through the evaporation of water off of its own respiratory system. So, though we are decreasing house air temperature using evaporative cooling, we are adversely affecting the bird's primary method of cooling itself because we are increasing humidity. In the case of the plastic pad, the higher house temperatures are accompanied by a significantly lower relative humidity, which makes it easier for a bird to lose heat through the evaporation of water off its respiratory system i.e. So, though wind speed is less effective in removing heat from the birds because it is closer to the bird's body temperature, the bird is losing more heat through the evaporation of moisture off its respiratory system because the relative humidity is lower. The question of course is, are birds better off in the plastic pad house or the paper pad house? The answer comes down to how warm a house becomes on a hot summer day.
The primary objective of any evaporative cooling system is to keep the incoming air temperature 85°F or lower during hot weather when market age birds are present. Once the temperature starts to rise above 85°F, the cooling produced through the movement of air over their bodies starts to decrease to critical levels. If the air temperature in a house rises above 90°F, the cooling produced by air movement is reduced to such an extent that mortality is likely to occur with market-age birds. During the extremely hot-weather flock, both systems were successful for the most part in keeping the incoming air temperature below 85°F, but the paper pad system was generally able to maintain an incoming air temperature closer to 80°F (Figure 6).
The problem for the birds in the house with plastic pads was that though the incoming air temperatures tended to remain below 85°F, temperatures within the house were often between 85 and 90°F during the hottest part of the day (Figure 7). The higher temperatures resulted in the air moving down the house removing less heat from the birds. This is verified by the fact that with all the fans running, during the hottest portions of the day, the temperature difference between the inlet and fan ends of the house decreased to less than 3°F. This is contrasted in the paper pad house where the temperature difference between the pad and fan ends, with the same number of fans operating, was closer to 5°F (Figure 8). Since in a totally enclosed house it is primary the bird heat that causes the temperature to rise as the air moves from the pads to the fan, all things being equal (house construction, number of fans running, house tightness, etc.) a smaller temperature differential tends to indicate that the air moving down the house is doing a poorer job of removing heat from the birds. Yes, the lower relative humidity in the house with plastic pads would increase bird panting heat loss, but it is questionable whether it would be enough to offset the substantial reduction in heat loss due to hotter air moving over the birds.
Figure 7. Plastic pad house air temperatures.
Plastic Evaporative Cooling Pads...A First Look - Image 7
Figure 8. Paper pad house air temperatures
Plastic Evaporative Cooling Pads...A First Look - Image 8
Interestingly enough, the plastic pad system produced cooling similar to that which would be expected with a traditional twoinch paper fogging pad system (Figure 9). Though fogging pads did a relatively good job of cooling the birds during hot weather, many producers, especially those growing larger birds, felt that more cooling was needed to keep their birds comfortable especially during very hot weather. To increase bird cooling, most fogging pad houses were equipped with fairly substantial fogging systems, typically consisting of 60 to 120 one-gallon-per-hour nozzles and a 200 psi booster pump. With the addition of the interior nozzles most producers found that the fogging pad system could produce nearly the same amount of cooling as that of a six inch paper pad system. The interior nozzles would only be required as inside temperatures start to approach 85°F, which would generally coincide with outside temperatures in the mid nineties or higher. At this point the inside relative humidity would be low enough so that an interior fogging system could be used without the threat of substantial house wetting. Since the plastic pad system cooling efficiency is very similar to that of a two-inch paper fogging pad system, it would stand to reason that if a producer chose to install a plastic pad they would probably also need to install an interior fogging system for use when outside temperature climbed past the mid nineties.
Figure 9. Two inch fogging-pad system
Plastic Evaporative Cooling Pads...A First Look - Image 9
Figure 10. Interior of plastic pad after one year of use
Plastic Evaporative Cooling Pads...A First Look - Image 10
Another issue noted with the plastic pad system was its tendency to waste water. With the high water flow rates required to ensure the plastic pads stayed thoroughly wetted there was significant more sprayed on the ground around the system as compared to the paper pad system. Though this could have probably been reduced by reducing the amount of water flowing over the pad, it would have likely resulted in a reduction in cooling. It is important to note that the pads were installed in a distribution system which was designed to be able to circulate the large volume of water required to properly wet plastic pads. Had the pads been installed in a more typical "low volume" water distribution system i.e., one utilizing undersized submersible pumps, it is likely that the cooling produced by the pads would have been lower. Another factor to keep in mind is that plastic pads weigh significantly more than traditional paper pads (Dry weight of 11.25 vs. 2.5 lbs lbs per linear foot for a five-foot-tall pad). As a result plastic pads should only be installed in distribution systems capable of supporting the additional weight.
Figure 11. Unglued piece of plastic pad
Plastic Evaporative Cooling Pads...A First Look - Image 11
One year after the installation of the plastic pad there appeared to be relatively minimum buildup of dirt and minerals on the pad (Figure 9). The lack of mineral buildup on the pad was expected due to the farm's overall good water quality. There were a few instances of the glue holding the pieces of the pad together coming loose, but overall the plastic pads have held up very well (Figure 11). It is important to note that as with paper pads, over time as dirt and dust accumulate in the pad, the cooling produced by the pad will tend to increase. This is because the dirt in the pad will not result in increased pad surface area, but will tend to improve the wicking ability of the pad. But, the increase in cooling will be slight, possibly a degree or so during very hot and dry weather. The other thing to keep in mind is that though the cooling produced by the pads could increase when they get dirty, the air flow through the pad/house could be reduced, possibly resulting in an overall decrease in bird cooling.
Plastic pads are probably not for the typical poultry farm. Many producers would likely find the reduced cooling, higher initial cost, and/or the need for a significant number of interior fogging nozzles to increase cooling to that of a traditional six-inch paper troublesome. That being said, if a producer has highly basic water, the need to sanitize their pads, or possibly water with very high mineral content, a plastic pad could be a possible option. As to how the pads will hold up over multiple seasons and or frequent cleanings with possibly very strong cleaners to remove mineral buildup, that remains to be seen.
This article was originally published at UGA Cooperative Extension Poultry Housing Tips Vol. 24 no. 8, August, 2012. Engormix.com thanks the authors for this huge contribution. 
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Authors:
Mike Czarick
University of Georgia
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Dr. Brian D. Fairchild
University of Georgia
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Mike Czarick
University of Georgia
4 de marzo de 2015
The plastic pad will cool similarly to a traditional paper pad. Since a plastic pad has a slightly lower cooling efficiency it will produce slightly less cooling with slightly less humidity.
Mike Czarick
University of Georgia
17 de julio de 2014
my pleasure. I enjoyed your thoughtful questions.
Mike Czarick
University of Georgia
17 de julio de 2014
In the U.S. (and most of the world) we use a 15 cm Celdek 45 X 15 flute angle pad. The static pressure drop at 1.5 m/sec is 10 Pa which is basically the same as the hewitech plastic pad (what we saw/measured in the field). Their is no difference in pressure drop at the same velocity therefore there would be basically no difference in fan performance. The cooling efficiency of the Celdek 45 X 15 pad is in fact higher than the plastic pad which would result in a reduction in air cooling.
Mike Czarick
University of Georgia
17 de julio de 2014
To analyze an evaporative cooling pad you need both a static pressure curve AND a cooling efficiency curve. You mention that a plastic pad has a lower static pressure drop but did it have the same cooling efficiency...at the same surface velocity. Secondly how much the air exchange rate would change depends on exactly the static pressure was decreased. The fact is that a 30% decrease in pressure could have a minimal effect on air exchange rates.
Mike Czarick
University of Georgia
13 de septiembre de 2012

It is always nice to hear from our friends in Pakistan. Please let us know if we can every be of assistance.

Mike Czarick

Mike Czarick
University of Georgia
7 de septiembre de 2012
Brick pads can produce some level of evaporative cooling, but it will be less than traditional paper pads. How much less depends on a variety of factors such as air speed through the pad, outside temperature, relative humidity, and amount of water placed on the pad. The reason that a paper pad will produce more cooling basically comes down to surface area. A paper pad typically has at least 10 times the surface area of a "brick" pad. Another thing to keep in mind that the humidity a pad produces is proportional to cooling produced by a pad. For every 1 C cooling an evaporative cooling pad will increase the Rh 5%. This is true for ANY pad or fogging system. The reason a brick pad produces less rh is that it is producing less cooling. 5 C less cooling....25% less humidity. You cannot get the same level of cooling without producing the same level of Rh. Hope this helps. mike czarick
Joseph Farah
6 de junio de 2022
Who is the main manufacturer of the plastic cooling pads in Europe??
mojtaba abedini
24 de mayo de 2015
hi pleas send me method of Removal of odor from the cooling pad
bhaskar rao
4 de marzo de 2015
Dr . Mike, is this the explanation to my Query. I need a more detailed response & would love to have more members discuss it.
bhaskar rao
4 de marzo de 2015
Sir, Wanted to have the relative humidity and temperature data during hot humid months inside the greenhouse which has a plastic evaporative cooling pad compared to the ambient. Has this system been employed in the Middle East ( gulf countries) for agricultural/livestock production. Here in Bahrain we do have high humidity & high temperature during June to August/sept, so how far will this plastic pad be effective.
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