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How does central air conditioning work

The central air conditioning system

By definition, a central air conditioner is an air conditioning unit that provides cooling to an entire home or building from one centralized source. This is typically facilitated by an air duct system running throughout the entire home or building connected to an air handler (often times a furnace) that houses a large blower used to pull in air from the rooms, pass it through the air conditioner and return the cooled air back to the house or building.

The components of a central air conditioner

The central air conditioner consists of 4 main operating components:

  1. The air handler or furnace blower
  2. The evaporator coil (sometimes referred to as an A-coil)
  3. The line set and refrigerant
  4. The outdoor compressor

The blower motor

The blower motor of the air handler or furnace is what is used by the air conditioning unit to both pull in the warm air from the home or building that needs to be cooled and then redistributes the cool conditioned air back through the house or building.

The evaporator coil

The evaporator coil (sometimes referred to as an A-coil because of its shape) sits on top of the furnace or in the air handler, so it’s not visible to the naked eye. It’s within this coil that the cooling process takes place. The coil is filled with liquid refrigerant and when warm air from the house is passed through it, the liquid refrigerant absorbs the heat which boils it and turns it into a gas (the process of evaporation). So as you can see, it’s not so much cooling the air but rather removing heat from the air which lowers its temperature. The cooler air is then distributed throughout the house or building.

The line set and refrigerant

The line set consists of two copper tubes running from the evaporator coil inside the house or building to the compressor sitting outside. The smaller tube, also referred to as the high pressure line, contains the liquid refrigerant coming from the outside compressor which is deposited into the evaporator coil. The larger tube, also referred to as the low pressure line, contains the gaseous refrigerant from the evaporation cooling process and flows to the outdoor compressor. The refrigerant used today is called R410A (also known by the brand name Puron). Prior to 2010, R-22 refrigerant was still used (also known by the brand name Freon) but has since been banned due to its harmful effects to the ozone layer.

The outdoor compressor

The outdoor compressor receives the gaseous refrigerant from the evaporation cooling process and compresses the gas turning it back into a liquid. This change of state process releases the heat that was absorbed by the refrigerant in the cooling process, expelling it to the outside atmosphere. The resultant liquid refrigerant is than pumped back into the evaporator coil in the home or building, ready to begin the cooling process all over again.

The efficiency of a central air conditioner

The efficiency of a cooling unit is measured in either SEER (Seasonal Energy Efficiency Ratio) or EER (Energy Efficiency Ratio). SEER is simply the seasonal average of the EER. In Canada, the SEER rating is predominantly used by manufacturers to denote efficiency and the higher the rating, the higher the efficiency level of the unit. In Canada, the minimum SEER requirement for new units is 13 and some manufacturers produce models as high as 21 SEER.