why are evaporative coolers ineffective in humid weather?

Question

I want to know exactly the connection between humidity and the functioning of water coolers.

Answer 1

Well, "water cooler" is not the same as "evaporative cooler." Water cooler is another name for a drinking fountain. So humidity has nothing to do with how it works.

But what you really want to know about is evaporative coolers. Their cooling is a result of the evaporation of water into the atmosphere. As the water evaporates, it absorbs heat. (It takes ENERGY to turn liquid water into water vapor, so this energy is absorbed from the surrounding water, cooling it.)

When the weather is humid (i.e., when there is a lot of water vapor in the air), less water evaporates from the evaporative cooler, so less cooling occurs. Actually, what happens is that water molecules evaporate into the atmosphere (absorbing heat energy), but water vapor molecules in the atmosphere condense (giving off heat energy). So the more humid the air is, the less NET cooling occurs. ("Net cooling" means the cooling effect from evaporation, less the heating effect from condensation.)

Answer 2

The wet bulb thermometer principle can be applied to this case.When the air is dry, the water that is sucked by the wick evaporates at a faster rate causing more cooling which in turn lowers the temperature of the wet bulb thermometer.If the air is humid evaporation is less and the cooling also is less.We can give another example also. Water kept in a mud pot cools faster when there is dry air due to the evaporation of the water which is oozing out whereas if there is humid air it does not cool at all as no evaporation takes place.Hence evaporative coolers are ineffective due to a similar reason.

Answer 3

Evaporative coolers work because it takes a considerable amount of heat to evaporate water. Thus, they remove heat from the air but at the same time raise the humidity of the air. When the humidity is high not as much water can evaporate and the cooler becomes less efficient. Not as much water can evaporate because the air is becoming saturated at higher humidities.