How does an air conditioning system work?


If you live in a hot climate, there is nothing better than keeping cool by using an air conditioning system. But how exactly do they work?

Here we try to answer that question and explore what types of AC systems exist. As Heating, Ventilation and Air Conditioning (HVAC) is a very complex field of engineering, we should note that this is not a comprehensive guide and should be taken as a brief overview.


How does an air conditioner work?

In short, they work just like your average kitchen refrigerator. The technology behind air conditioning systems and refrigerators is exactly the same – the refrigeration cycle.

Systems that take advantage of this cycle use special chemicals called refrigerants (water in some systems) to absorb and / or release energy to heat or cool air. When these chemicals are compressed by the AC unit compressor, the refrigerant changes state from gas to liquid and releases heat at the condenser.

When cooling a space, this process occurs outside the space in question. This high pressure air, which is now cold, is pumped to the indoor unit and expanded to gas using the system. Expansion valve.

This, as the name suggests, causes the re-expansion of the refrigerant liquid in gaseous form. As the refrigerant expands, it “sucks” heat and cools the air in the space in question at the air conditioning system. evaporator.

This now expanded and “hot” gas is then transported to the system compressor and the cycle begins again.

To visualize this, think of a sponge as coolant and water as “heat”. When you squeeze a soggy sponge (the compressor and condenser), water is expelled and heat is released in our analogy. When you let go of the sponge (the expansion valve and the evaporator), it expands and can then absorb more water or heat in our analogy.

The basic foundation of this cycle is the scientific principles of thermodynamics, Boyle’s law, Charles’s law and Guy-Lussac’s laws.

Mainly the fact “an expanding liquid in a gas extracts or draws heat from its surroundings. “- Air conditioning and heating Goodman.

In this sense, air conditioning and refrigerators work by “moving” or “pumping” energy from one place to another. In most cases, AC units will transfer the “heat” from your room, office, or home, and release it into the air outside your home or office.

Source: Pixabay

This cycle is reversible and can be used to also heat your room, or your entire home, during the colder months, but this feature is usually reserved for systems called heat pumps.

The main difference between a refrigerator and an AC unit is that the unit tends to be split into two separate parts; the outdoor unit of the condenser (or chiller) and the indoor unit.

Refrigerators, on the other hand, are a stand-alone unit (although some AC units can be as well).

Any heat extracted from its interior is discharged into the same room at the back of the unit. This is the main reason why you could never really use a refrigerator as a DIY air conditioning unit; unless you perceive a hole in the wall behind, of course.

You can test this by touching (be careful, it can get very hot) the back of the refrigerator when it is in use. It should be warm or warm to the touch.

What are the different types of air conditioning systems?

AC units come in many shapes and sizes today, ranging from massive duct systems in offices and industrial buildings to the smaller household AC systems you are probably more familiar with.

Some of the larger facilities have very large outdoor cooling units which can be water or air cooled or, in older systems, cooling towers. These are connected by insulated pipes to pump the refrigerant to temper the air in a large or a set of large packaged units called air handling units (AHUs).

These systems can be very complex with heaters and humidifiers, and filters to very precisely control the temperature and air quality for the areas of a building they serve. They also tend to come with complex heat recovery systems to reduce the amount of electricity (or gas) needed to heat / cool the air in the system.

They come in two main forms; Constant air volume (CAV) and variable air volume (VAV), which defines how much airflow is controlled around system ducts.

These can also be controlled by very sophisticated software, sensor and actuator systems called Building management systems (BMS).

These large HVAC systems “suck in” fresh outside air and heat / cool it as needed before transporting it through ductwork to required areas. These systems may also have reheating terminal units, Where fan coils, to further refine the quenching of the air supplied to an area.

More modern installations do away with centralized air handling units in favor of fan coil systems, or “indoor units” which are directly linked to one or more “outdoor” AC units. These are called Variable refrigeration flow (VRF) which temper the air directly at the point of use.

But most people are used to air-to-air heat pumps (ASHP) or single room air conditioning units. These are much more like refrigerators and are the systems most often installed in domestic premises.

But it should also be noted that there are various other systems, using the same principle, such as geothermal heat pumps (GSHP). These use the soil as a “dumping ground”, or source of heat, instead of air or a source of heat. ASHPs and GSHPs can also connect to ordinary radiator systems or underfloor heating systems in place of a regular gas boiler with some modifications.

How does air conditioning work in cars?

Simply put, AC in cars works exactly the same as any other AC unit. The only difference being that they have to be compact enough to fit inside the car.

The cooler part of the system (with the expansion valve and the evaporator) is usually mounted behind the car dashboard. The other commercial end of the system (the compressor and condenser) tends to be located near the grille of the car – this is where cool air is blown in while you are driving).

The two parts are connected by a circuit of pipes which pass the refrigerant between the units when they are in operation. Unlike the larger units used in buildings, the unit itself in cars tends to be powered by the car’s crankshaft, in other words, it is powered by the engine.

These systems are usually equipped with heaters and dehumidifiers to temper the air as needed. Just like building air conditioning systems, a car’s air conditioning unit will convert coolant between gas and liquid, high and low pressure, and high and low temperature as needed.

Is it cheaper to leave the air conditioner on all day?

Simply put, no. The reason is that by leaving a AC system all day :

1. Use energy unnecessarily if you are not at home or rooms / areas are not being used.

2. System execution wears and tears. This shortens the life of it.

You should also make sure that the windows are closed or that a draft shield is installed when the air conditioner is operating. You don’t want to “air-condition” the world after all.

You should also make sure that you use shading devices (like an awning or strategically planted trees) outdoors to reduce “solar gain” or passive heating of your home by sunlight.

Other measures include improving your home’s insulation, maintaining air conditioning systems (especially filters), and using ceiling fans to improve indoor air mixing (ie. (i.e. prevent stratification of hot air near the ceiling or vice versa).

If you are really concerned about your energy bills related to your air conditioning systems, you might want to make your air conditioning system “smarter”. By using home BMS, smart sensors (thermostats and weather compensation), zone control, and other energy efficiency measures, you can dramatically improve the efficiency and lower the cost of your AC systems.

You should also use “free” cooling and heating solutions, considering using nature to help you. Proper use of natural ventilation to cool or heat your home will drastically reduce the cost of heating / cooling energy consumption by turning it off.

But this is only possible if the quality of the air outside your home allows it. Living in a large city with “dirty air”, for example, might restrict your ability to use this free form of heating and cooling.

How does reversible air conditioning work?

Reverse cycle air conditioning systems, or heat pumps as they are more commonly called, work in much the same way as any other form of air conditioning unit. The exception being that they are specifically designed to be able to reverse the cycle at will.

Like other AC systems, they can also filter and dehumidify the air as needed.