The question is often asked: "I know that evaporative cooling is practical in dry climates, but will it work in the more humid areas?"
You can determine this by the use of a psychrometer. When a wet bulb depression of 18 to 20 degrees or more consistently occurs during the time when cooling is needed, satisfactory conditions can be obtained through the use of evaporative cooling. Comfort cooling from evaporative coolers comes in two ways:
1. The lowered dry bulb temperature of the air, and
2. The movement of air over the people.
The amount of dry bulb temperature reduction possible at the cooler outlet discharge varies with the local climatic conditions, because it is limited by the wet bulb depression and the use of evaporative cooling should be on the basis of comfort, never on the promise of a certain number of degrees of temperature reduction. Use the following rules for a successful installation:
1. Size the Cooler Large Enough. Do not, under any circumstances, sell a cooler that is not the proper size. Understand and use the information given in this section on sizing evaporative coolers. An undersized cooler can make conditions worse than no cooling. When in doubt always use the next larger size.
2. Supply Fresh Outdoor Air to the Cooler. Never use room air; never recirculate the air. Remember, the cooler depends on the evaporation of water for cooling the air. Once the air is saturated with water there can be no further evaporation of water for cooling the air. Never violate this rule.
3. Exhaust the Spent Air. As a corollary to Rule 2, let the air out of the cooled space as fast as the cooler brings in new cooled air. To do otherwise will result in room conditions worse than no cooling.
4. Be Sure the Customer Knows the Limitations. The final conditions depend upon the climate that nature provides. The theme should be "Comfort ninety per cent of the time, with relief from the heat the other ten percent of the time, at a fraction of the cost of refrigeration.
