The most common and cost efficient cooling device is the room air conditioner. This consists of indoor and outdoor portions. An air filter, a fan and a cooling coil are parts of the indoor portion. The warm, humid air is drawn through the filter and into the fan then blown over the cooling coil. The cooling coil then cools and humidifies the air before it is blown into the room. The cooling coil contains a refrigerant fluid, which changes its physical property from liquid to gas because heat from the warm air passing over the coil causes its evaporation. Heat from the warm and humid room air is taken through this process. The outdoor portion of the unit consists of a compressor, a fan and a condenser. The cooling coil gives off low-temperature and low-pressure refrigerant gas to the compressor. The compressor on the other hand delivers high-temperature and high-pressure refrigerant gas to the condenser. The fan blows outdoor air over the condenser. Inside the condenser the high temperature, high pressure refrigerant gas is converted to refrigerant liquid. Heat from the hotter refrigerant gas is taken by the cooler outdoor air passing over the condenser.
This process causes the refrigerant gas to change to the liquid state. The refrigerant fluid circulates through the closed path leading through the cooling coil, the compressor and the condenser in a constant motion. The relatively cool outdoor air is sucked by the fan for cooling the condenser and then blows the hotter air back outdoors. In a room air conditioner, electric motors drive the compressor and the two fans. 110-volt lines are used for smaller room air conditioning units while for larger units 220 volt line supplies are used. An entire small residence can be cooled by some room air conditioners with sufficient capacity.
Although a room air conditioner is the lowest-cost cooling device, it has its own disadvantages which include the following:
1. Most room units can provide only widely irregular room air temperature.
2. Most room air conditioners operate with noise.
3. It is difficult to obtain an even distribution of cool air.
Because of the known disadvantages of a room air conditioner many people prefer to use the more expensive central cooling system.
A central cooling system is commonly divided into two units: An indoor and an outdoor unit. A filter, a fan and a cooling coil constitute the indoor unit. The outdoor unit on the other hand consists of a compressor that is motor-driven, a fan for the condenser and a condenser. A cabinet mounted outdoors houses these components. Most home cooling systems provide humidity reduction but offer only very limited humidity control. The length of the compressor operation determines the moisture content reduction. For example, a low indoor humidity value of 40 percent is reached when the compressor operates continuously for several hours during a hot summer day, but as night time approaches and the compressor stops operating, the water drops on the cooling coil tend to evaporate and a jump in the indoor humidity occurs. This variable humidity and its limited control however, are acceptable to home owners who are using the central cooling system.
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