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Scale and mineral deposits form on the face of the cooling pad because the mineral content in the water is too high. Control scale by:
Proper water distribution is the single most important way of prolonging pad life. The water will flush away dirt and contaminants which may be harmful to the pad. Areas “starved” for water will often be the first to clog or soften.
In most systems, calcium carbonate and silica are the most troublesome of scale formers. Silica is the most straightforward. It must be kept at a concentration less than 150 PPM.
Calcium carbonate scaling is more dependent on alkalinity (an indication of pH). Its solubility can be simplified to a curve of calcium carbonate concentration versus alkalinity. On the chart, notice that stable water is represented by the narrow line. Water quality to the right of the line forms scale. Water to the left of the line is scale dissolving or corrosive. It is difficult to keep water perfectly balanced. Instead, try to keep the water reasonably close to the line so that it fluctuates between scale forming and scale dissolving.
When water evaporates, only pure water is released. The dirt and harmful chemicals are left behind with the water on the pads and in the sump. Eventually, the water becomes so contaminated that it is harmful to the pad.
Algae needs three elements to survive:
Normally evaporative coolers on GT inlets are downstream of weather hoods or louvers and often downstream of filters. So in most inlets sunlight and therefore algae growth will not be an issue. Algae only needs sunlight for a few hours each day. If sunlight can be minimalized, the growth period will also be shortened. Locate pads or protect from sunlight. Do not use clear or translucent hoses, pipes, tanks of water distribution systems. If inlet louvers are used, a dark color will reduce the sunlight.
Algae feeds off the nutrients in the water and air, not from a “good” cooling pad. Look for sources of nutrients and try to eliminate them. Nearby farm fields and roads contribute dust and fertilizer which can be drawn through a lower efficiency filtration system into the pads. If algae growth occurs on the cooling media it is best to replace the media.
Do not use phosphate type scale control agents or detergents on the pads. They degrade to form phosphate type nutrients.
Most evaporative coolers in GT Inlets are designed using stainless steel for all wetted metal components. This is “best practice” in design and construction. Look for materials that are not stainless steel and replace them as needed at the next possible planned outage.
There are four major forms of corrosive attack to evaporative cooling equipment.
Pitting is the removal of metal at the surface in small, localized sites. These sites start out as inconspicuous flecks of rust or oxide, and eventually eat their way through gutters and pans in saucer like depressions. Pitting is usually caused by the presence of copper, sodium chloride, sulphur and other strong contaminants in the water. The chemicals in a droplet of water are the most concentrated as the droplet dries. Avoid wetting and drying cycles, splashing and dripping where water can become concentration.
Crevice corrosion occurs in lap joints exposed to air and moisture. For aluminum and galvanized steel, oxygen must be present for corrosion to occur. For stainless steel, oxygen will help form a protective layer on its surface. To avoid this form of corrosion, joints should be well caulked with a caulking compatible with the metal. Read the label carefully and contact your cooler manufacturer for recommendations. Notice that some caulks should not be used with certain metals.
Galvanic corrosion occurs when dissimilar metals are used in the same system. Even when they are not touching, the corrosion can occur through the water. Avoid mixing aluminum, stainless steel and galvanized steel in the same system. Pay special attention to pumps, screws and valves. When metals must be mixed in the system, the odd metal should have a heavy protective coating, and transition joints should be used.
Poultice corrosion is due to contact with nonmetals. It may cause some serious problems. Materials such as cork, wood, cloth or paper provide moisture and air which contribute to corrosion. If they have been treated with a certain fire retardants or biocides (such as copper arsenite) the attack could be very severe. To prevent attack, coat the metal surface, or keep the porous material from becoming wet.
The leading edge of any evaporative cooling system is exposed to the harshest and highest velocity of contaminants. The first 1/2" of media gets more hot dry air and is where the highest evaporation takes place.