Understanding Your Central Air Conditioner – Basic Terms and Components

How operational your central air conditioner system can make or break your summer. There’s nothing worse than trying to sleep through a hot and humid night. Having a basic knowledge of your air conditioning system can help you determine if repairs are needed or will help you understand the HVAC technician when they come to do your yearly tune-up and inspection.

Basic Terms:

BTU – British Thermal Unit – this measurement of energy is the amount of energy needed to raise one pound of water by one degree Fahrenheit. For air conditioners, BTUs measure how much heat an air conditioner can remove from a room over the course of an hour.

Capacity – an air conditioner’s capacity is a measurement of how quickly heat is removed from an air conditioned space. The cooling load of a room (how much heat builds up in a space without any A.C.) is needed to determine the conditioner’s capacity. A ton is a measure of capacity. One ton of cooling capacity equals 12,000 BTUs.

Energy Efficiency Ratio (EER) – this is a measurement of how much cooling the air conditioner provides by how much electrical energy it uses when continuously operating for a specific amount of time. Air conditioner manufacturers must determine the EER of their units in order to meet the qualifications of Canadian Energy Efficiency Regulations and be given the EnerGuide label of approval. The higher the EER, the more efficient the air conditioner is. The units with the highest level of efficiency are given the Energy Star label and are determined to save a customer 30-40% in utility costs as compared with a unit sold 15 years ago.

Bel (B) – a measurement of sound which equals 10 decibels (dB). Some Ontario municipalities have by-laws which regulate how loud an air conditioner is during operation. Plus, the sound can be annoying for you or for your neighbours.

Central Air Conditioner Components

Condensing Unit – the outdoor unit which cools the hot inside air and sends it inside to the indoor unit. It contains a compressor, fan, condenser coil, refrigerant and evaporator coil.

Air Handler – the indoor component of the central which takes the cool air from the outdoor unit and sends it through the ductwork, through the house – most often a gas furnace, without the heat

Refrigerant – the fluid which runs through the unit and works by absorbing and releasing the heat

Coil – a series of looped tubes which the refrigerant runs through and where the heat transfer happens

Expansion Device – changes the refrigerant liquid into a low-pressure gas/liquid mix (vapour)

Evaporator Coil (indoor coil) – takes the remaining liquid refrigerant (after it’s been through the expansion device) absorbs the heat, boils and turns into a low-temperature gas

Compressor – the refrigerant gas molecules get compressed to increase the pressure and temperature, turning into a vapour 

Condenser Coil (outdoor coil) – allows the refrigerant vapour to give off its heat to the outside air after being compressed and once again become a liquid