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Central Air Conditioning Facts

The most common mistake made when installing a new central air conditioning system, as shown in Figure 1, is buying a system that has a larger cooling capacity than is required. In order for a central air conditioning system to produce the required result, a feeling of comfort in the room(s) that are being cooled, the system must not only lower air temperature, but it must lower the humidity.

Central air conditioner
Figure 1 - Central air conditioner

Dehumidification is as important, if not more important than the cooling ability of the system, as humidity generally supplies more personal discomfort than heat. For an air conditioning system to remove the humidity the fan must be running, in order for the fan to run the thermostat must be asking for cooling. A system that is oversized will not be circulating the air, hence it will reduce the temperature, but will not lower the humidity.

Central air conditioning systems, designed for homes, that provide cooling and dehumidification are made up of a condenser, evaporator coil, and refrigerant piping. This type of system is termed a split system, (the condenser and evaporation coil are not contained within the same housing). With a wall or window, air conditioner the condenser and evaporation coil are in the same housing. In most cases, the air is circulated utilizing the furnace’s air handler. However, in some cases the air handler will be an independent unit. The refrigerant is compressed and run through a series of tubes to remove as much heat as possible, then piped to an evaporator coil as a warm liquid. Expansion of the compressed liquid causes it to cool, and as the air passes over the coil, heat is extracted. The cool liquid becomes a cool gas as it gathers heat from the air, and is drawn back to the compressor to start the procedure again. As the air passes over the evaporator coil and cools, moisture in the air condenses and drains off as condensate, reducing the humidity level of the air in the premises.

As an alternative, some air conditioning systems use cold water instead of refrigerants however, this is much more common in commercial systems.

Most residential central air conditioning systems are considered low velocity. The air temperature will be lowered 15 to 18 degrees Fahrenheit as the air passes through the cooling coils. A six inch round duct is capable of delivering 2,500 BTU’s of cooling.

Recently an alternative to the standard ducted split air conditioning system has been produced for retrofit into older homes that do not currently have forced air ducting. This type of system operates at a high velocity and produces a 30 degree Fahrenheit drop. Because of the high velocity the system can deliver 2,500 BTU’s of cooling through a two inch round duct.

Most air conditioners have their capacity rated in British Thermal Units (BTU). Generally speaking, a BTU is the amount of heat required to raise the temperature of one pound (0.45 kg) of water 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1,055 joules. In heating and cooling terms, 1 ton equals 12,000 BTU.

The Energy Efficiency Rating (EER) of an air conditioner is its BTU rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts).

Central air conditioning systems require preventative maintenance in order to ensure trouble free operation.

About one-seventh of all the electricity generated in the US is used to air condition buildings.

Proper planning and knowledge will make a big difference in the overall success and satisfaction with your next home improvement project.

Earning the ENERGY STAR means products meet strict energy efficiency guidelines set by the US Environmental Protection Agency and the Department of Energy.

ENERGY STAR qualified central air conditioners have a higher seasonal efficiency rating (SEER) than standard models, which makes them about 8% more efficient.

Remember, saving energy prevents pollution. By choosing ENERGY STAR and taking steps to optimize the performance of your cooling equipment, you are helping to prevent global warming and promoting cleaner air while enhancing the comfort of your home.

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