Air Conditioner Based on Evaporation Principle
The important property of water of absorbing the ambient temperature while evaporating has been exploited to cool houses since the early ages. Even today the coolers based on evaporative technology use the above feature of water extensively.
The figure alongside shows the internal mechanism of a standard air cooler, also called a swamp cooler, based on the evaporative principle.
As we can see the entire process takes place inside a rather large box type enclosure.
The side walls of the enclosure have slotted ventilations for the surrounding warm air to get in.
A layer of thick spongy pad is placed immediately after the side ventilations inside the box.
A small electric water pump is used to transfer water from the bottom reservoir over these pads from the top so that they are properly soaked. The excess water drips down back into the reservoir.
A motor/pulley mechanism is used to rotate the propeller of a large fan at the front of the box. When it starts moving, the surrounding air is sucked inside the box through the side ventilations.
The air is dragged in through the water soaked pads where due to evaporation the sucked air loses its temperature and becomes cool.
The cooled air is ultimately forced out by the fan outside into the room, for the desired cooling.
The above principle may be enforced or implemented through different ways and may also be enhanced through new innovations.
For example, water sprinklers are used over the roofs of many houses where the water droplets evaporate helping the house to lower their internal temperature. The principle has been thoroughly studied and improved by NREL and they have succeeded in building a super efficient air conditioner entirely based on evaporative technology.
Although quite cheaper than an ammonia air conditioner, a swamp cooler may be accompanied with certain drawbacks. Here, the evaporated water molecules are distributed into the premise, unnecessarily increasing the relative humidity of the room. This can become a big nuisance especially for the coastal countries where the RH remains already on the higher side for most months. Also the efficiency of these units drastically fall as the surrounding humidity increases.
In our present design of homemade air conditioner, we rather take a different approach and use cold water to produce the required cooling effect, but not in a evaporative manner. This is a bit costly than the swamp coolers, but surely way ahead as far as the efficiency is concerned.