How air conditioner works and what is the work of ac outdoor fan?


How air conditioner works and what is the work of ac outdoor fan?

In: Engineering

As You compress gas, it gets hotter, like the hand pump on your bike tyre. Then this compressed hotter gas goes through a radiator to release heat (the outside fan). Then when this compressed/cooled gas is expanded it cools down like a deodorant can gets cool when you expand its compressed contents. Then this cooler gas is run through another radiator with a fan blowing air through it (inside fan).

In order to go from a liquid to gas (evaporate) the liquid needs a supply of energy (heat). Your AC has liquid refrigerant which can evaporate at very low temperatures and the heat it uses to do that it extracts from the air inside your house, cooling it down. Fans then blow that cool air out of the AC unit.

The (now hot) coolant gas is pumped outside the house. A compressor outside the house pressurizes the gas and then outputs it into a condenser. The condenser converts the pressurized gas back into a liquid. Just as going from liquid to gas requires an input of heat from the environment, going from gas to liquid results in an *output* of heat to the environment. The fan in the outside unit pumps the hot air away.

The (now cold) coolant liquid is pumped back inside the house where it can cool down more air.

The outside part is the compressor and condenser. Its job is to remove the heat from the inside of the house. Inside (located in the sheet metal box (plenum) above your furnace, assuming central AC is a similar set up. But instead of a compressor is a metering valve (think of it as an ‘expander’, the opposite of a compressor). When the high pressure liquid passes through the valve, it enters a low pressure area. The low pressure causes the liquid to boil and turn to gas, which absorbs heat from the surrounding area (which is why it’s cold). That low pressure gas goes to the compressor, which turns it into a high pressure gas which forces it back into a liquid which requires it to dump all that excess heat.

Confusing, I know, but if you look up ‘refrigeration cycle’ on google/youtube, there’s some really good animations out there.

The thing to keep in mind is that the refrigerant goes around in circles. If you draw a line through the compressor and metering valve (TXV, orifice etc) you’ll split the circle into two halves. Everything from the compressor to the metering valve is under high pressure, everything from the metering valve back up to the compressor is low pressure (aka suction). Each side has a set of coils. The low pressure coils (in the house) absorb heat, the high pressure coils (outside) reject the heat.

This is the exact same way (more or less) your car AC works, your refrigerator, your dehumidifier and most anything else that uses compressed refrigerant.


For a not entirely correct comparison. Think about what happens when you spray a bottle of canned duster. The can gets cold to the touch, right. That’s because the pressure is lowering inside the can (same for the liquid coming out of the end, it’s boiling off and also cold. If you could capture all that air coming out and shove it back in the can, it would make the can hot.

So, imagine spraying all that canned air into a bag while sitting in your house. Once all the cold dissipates (that is, it’s absorbed enough heat from the house to bring it to the same temperature as the ambient air), you then take the whole thing outside and compress it back into the bottle, and let the heat dissipate outside….that’s your refrigeration cycle. You absorbed heat from the house and dumped it outside.

it works by moving heat from the inside to the outside. the outdoor fan makes sure that that heat can escape into the air, even if it is a hot day outside. the technical explanation for how it does that is by changing the boiling point of the refrigerant. putting a fluid under pressure raises the boiling point, so on the outside unit, there is a compressor that makes one side of the system have high pressure, and on the inside of the house, an air handler that releases that pressure, so the other half is low. both sides move the refrigerant through radiators, but the inside is removing heat from the air blowing across it, and the outside is dumping heat.