Air conditioning is genuinely clever technology that most people use without really understanding. Here is a plain English explanation of how it works — which also helps explain why it is so much more efficient than electric heating.
The Basic Principle — Moving Heat, Not Creating Cold
The key insight about air conditioning is that it does not create cold — it moves heat. Cooling a room with air conditioning means moving the heat from inside the room to outside. This is fundamentally different from an electric heater, which creates heat by converting electricity directly into thermal energy. Moving heat is much more efficient than creating it — which is why air conditioning uses significantly less electricity than electric heating for equivalent thermal output.
The Refrigeration Cycle
Air conditioning works using the refrigeration cycle — the same process used in your fridge, freezer and car air conditioning. The key is that refrigerant — a specially chosen fluid — has a very low boiling point and can be manipulated to boil and condense at different pressures.
Inside your home (the evaporator): Refrigerant arrives at the indoor unit as a liquid at low pressure. As room air is blown across the indoor unit’s coil, the liquid refrigerant absorbs heat from the air and boils — turning from liquid to vapour. As it boils, it absorbs a large amount of heat (just as boiling water absorbs heat). The room air that has had heat removed from it is now colder — this is the cold air you feel from the unit. The refrigerant vapour, now carrying the room’s heat, travels in the pipework to the outdoor unit.
Outside your home (the condenser): The vapour refrigerant arrives at the outdoor unit and passes through the compressor, which increases its pressure. At high pressure, the refrigerant condenses back into liquid — releasing the heat it absorbed indoors into the outside air. The outdoor unit fan blows air across the outdoor coil to remove this heat — which is why the air coming from the outdoor unit is warm. The refrigerant, now liquid again, travels back to the indoor unit to begin the cycle again.
The Compressor — Heart of the System
The compressor is what makes the whole process work — it creates the pressure difference that allows the refrigerant to absorb heat at the indoor unit and release it at the outdoor unit. The compressor is powered by electricity, and this is the main electrical consumption of the air conditioning system.
Inverter Technology — Why Modern Systems Are So Efficient
Older air conditioning systems had fixed-speed compressors — they ran at full speed or not at all, switching on and off to maintain temperature. Modern inverter systems use variable-speed compressors that continuously adjust their speed to match the exact cooling demand. When the room is nearly at target temperature, the compressor runs slowly. When the room is much hotter than target, it runs fast. This continuous matching of output to demand is much more efficient than the old on/off approach — typically 30-50% more efficient for residential use.
Heat Pump Mode — Running in Reverse
All modern split system air conditioners also work in reverse — extracting heat from outside air and delivering it inside. This is the heat pump function. Even in cold weather, the outdoor air contains heat energy that the refrigerant can absorb (the outdoor unit coil gets colder than the outdoor air, allowing heat transfer into the refrigerant). This heat is then compressed and released indoors. The result: for every unit of electricity used to run the compressor, you get 3-4 units of heat delivered inside — making it 3-4 times more efficient than direct electric heating.
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