WORKING WITH WATER-COOLING PROBLEMS
Three-fourths of the earth’s surface is covered with water. The earth is blanketed with water vapor, which is an indispensable part of the atmosphere. Heat from the sun shining on oceans, rivers, and lakes evaporates some water into the atmosphere. Warm, moisture-laden air rises and cools. The cooling vapor condenses to form clouds. Wind currents carry clouds over land masses where the precipitation may occur in the form of rain, snow, or sleet. Because of the sun and upper-air currents, this process is repeated again and again. Pure water has no taste and no odor. Pure water, however, is actually a rarity.
All water found in oceans, rivers, lakes, streams, and wells contains various amounts of minerals picked up from the earth. Even rainwater is not completely pure. As rain falls to earth, it washes from the air various gases and solids such as oxygen, carbon dioxide, industrial gases, dust, and even bacteria. Some of this water sinks into the earth and collects in wells or forms underground streams. The remainder runs over the ground and finds its way back into various surface-water supplies.
Water is often referred to as the universal solvent. Water runs over and through the earth and mixes with many minerals. Some of these mineral solids are dissolved or disintegrated by water.
Pure water and sanitary water are the same as far as municipalities are concerned. “Pure” in this case means that the water is free from excessive quantities of germs and will not cause disease. Mineral salts or other substances in water do not have to be removed by water-treatment plants unless they affect sanitary conditions. Mineral salts are objectionable in water used for many other purposes. These uses include generating power, heating buildings, processing materials, and manufacturing. Water fit for human consumption is not necessarily acceptable for use in boilers or cooling equipment.
Water is used in many types of cooling systems. Heat removal is the main use of water in air condition- ing or refrigeration equipment. Typical uses include once-through condensers, open recirculating cooling systems employing cooling towers, evaporative condensers, chilled-water systems, and air washers. In evaporative condensers, once through systems and cooling towers, water removes heat from a refrigerant and then is either wasted or cooled by partial evaporation in air. Knowledge of impurities in water used in any of these systems aids in predicting possible problems and methods of preventing them.
Cooling towers are usually remotely located; it becomes necessary to regularly inspect and clean the tower according to the manufacturer’s recommendation. The few hours each month spent on inspecting the cool- ing tower and maintaining it will pay dividends. The life of a tower varies according to:
• Construction materials
• Location within the system
• Location of the city or country
Generally, the premium materials of construction are:
• Wood
• Concrete
• Stainless steel
• Fiberglass
These units are expected to last from 20 to 30 years if properly cared for. The less expensive units, made of galvanized steel, will operate for 8 to 20 years. Of course, tower life will vary due to the extremes of weather, number of hours used each year, and type of water treatment. It is sufficient to say that in order to get the most use from the tower, cooling tower manufacturers want to make that tower last as long as possible.