Evaporative cooling pads are used to cool down poultry house temperatures during hot weather all over the world. The efficacy of pads largely depends on how they are used and maintained. Life-span and performance can be improved by using lots of water.

By Michael Czarick, University of Georgia,Athens GA,USA*

In order to get maximum cooling as well as maximum life out of your sixinch evaporative cooling pad system, it is very important that the water distribution system is capable of circulating a minimum of 9 litres per minute for every meter (0,75 gallon/min/foot) of pad system length. This means, for instance, that a 18 m (60ft) pad section should have a water distribution system capable of circulating at minimum 160 litres of water per minute over and through the pads.

Before getting too concerned about total water use, you have to realize that only a small fraction of this water will actually evaporate. In fact, the recommended circulation rate is about ten times the maximum evaporation rate. So why do we need to circulate so much water? First, it is important to keep in mind that unlike the fogging pad system, with the six-inch pad system water is only applied at the very top of the pad and as a result it takes a lot of water to insure that the pads get thoroughly wetted all the way to the bottom. If insufficient water is applied, dry spots and streaking will occur.

Streaking will, of course, lead to decreased cooling as some of the air entering the house moves through sections of dry pad instead of wet pad.

Adjust amount of water

Just because your pads appear to be wetting properly today does not necessarily mean they are circulating the proper amount of water. During mild weather, it does not take much water to keep a pad thoroughly wetted because not very much water is evaporating. But the hotter it becomes outside, the more difficult it is to keep a pad thoroughly wetted, because the amount of water evaporated increases dramatically.

For instance, on a day when it is25 °C with 50% relative humidity, approximately 15 litres of water will evaporate off pads each minute in a typical 12.5-meter broiler house. But when it is 35°C with 20% relative humidity, water usage will more than double to over 30 litres per minute. So water flow that may suffice on a 25-27°C day may not be adequate to prevent streaking on a 35°C day when evaporation and the need for cooling are at their highest. Circulating the proper amount of water over a pad not only insures maximum cooling, but helps to minimize dust build-up. Water flowing over the surface of a pad actually helps to remove dust from the surface of the pad and to some extent the interior of the pad. It is the accumulation of dust on and within a pad which increases the static pressure the fans are working against. Increased static pressure reduces the exhaust fan’s air-moving capacity, leading to decreased wind chill and larger temperature differences between the pad and fan ends of the house.

Furthermore, the dust often contains ammonia, which can change the pH of the pads, making them softer over time and reducing their efficacy.

Water flow over a pad also helps minimize mineral build-up. When there is very little water flow over the surface of a pad, mineral deposits are more likely to form on the surface of the pad. Over time, if not removed, the accumulation of minerals will make it harder and harder for the exhaust fans to pull air into and down the house. The more water flow you have over the surface of a pad, the more likely that minerals in the water will be kept in suspension and airflow, as well as cooling, will be maximized.

Measure the spraying height

One of the easiest ways to check to see if you have sufficient water circulating over your pads is to simply take the top off of your distribution system and measure the height of the water that is spraying up from the holes in the top of your distribution pipe. How high the water should spray up depends on hole spacing as well as hole size. The smaller the holes or the farther the spacing, the higher the water has to spray up to supply the proper amount of water (see Table 1).

As you can see in the table, the heights that the water sprays upward vary significantly from system to system. Increasing the hole size from 1/8” to 5/32” dramatically decreases the height needed because a change of only 1/32” actually changes the area of each hole by approximately 55%, thereby significantly increasing the amount of water coming from each hole. Since the holes are so much larger, the water does not come out as fast (or spray up nearly as high) while supplying the same amount of water as the much smaller 1/8” hole. The table illustrates that putting the holes close together also reduces the amount of water column height required to produce 0.75 GPM/ft.

Flow uniformity

Another important aspect of your distribution system that you should examine is the uniformity of the water spraying out of your distribution pipe from one end to the other. If you consider the top of the distribution system near the pump and at the end of the system, you will notice that the water shoots up higher at the pump end of the system. This is because the decrease of water pressure and flow as you move from the pump to the end of the system. How much it changes depends on a variety of factors such as pipe size, hole spacing, and system length. In general, the further you move away from the pump, the less the water will spray up and the less water flow the pad will have. As a result, when checking the water flowing to your pad, it is recommended that you check at the end of the system where water flow will be generally be the lowest.

One problem with longer systems (over 15m/50’) is that there can be a big difference in water column height from one end of the system to the other. In these systems you may have over 20” of water column height at one end and less than 5” at the far end, leading to the possibility of excessive water at one end and insufficient water at the other. One possible solution is to install a larger pump. The problem is that, in order to get proper water flow at the far end of the system, the water pressure may be so high near the pump that water sprays out from underneath the distribution system, creating a mess. Furthermore, the larger pump will not only increase initial cost but operating costs as well. The best way to improve system uniformity is to simply place the pump in the centre of the evaporative cooling pad system. This reduces the water flow rate to the distribution pipe, thereby reducing friction and improving the uniformity of water flowing to the pads.

Download matéria completa: Circulação de água em Sistema de Painel Evaporativo (Pad Cooling) (1183)

WORLD POULTRY – Vol. 20 No 4. 2004 www.AgriWorld.nl 18
(* This article is an edited version of “Does your evaporative cooling pad distribution system circulate enough water?,”Poultry Housing Tips, Vo.14-no. 4)