How Does Air Conditioning Work?
The air conditioner is a technology which has enjoyed widespread use over the past century. They are vastly more efficient than their oil and gas-based counterparts and can be installed with minimal cost and disruption, as they do not require the installation of complicated networks of piping inside the interior walls of a building. For these reasons, they have proven attractive for homeowners and businesses alike. In the article that follows, we’ll take a look at how air conditioning works.
What does an air conditioner do?
When we think of an air conditioner, we imagine a large unit (or system of units) which spits out a stream of cold air. That’s not the extent of an air conditioner’s functionality, however – they aren’t, after all, known as ‘air coolers’. They can also heat the air. Also since cooling the air causes it to release some of the moisture it is carrying, they serve as dehumidifiers. This is why many air conditioners have built in drains and trays which collect the moisture released by the cooling air and why faulty air-conditioners might sometimes begin to drip water from the bottom.
A modern air conditioner can also monitor the air using a thermostat and then heat and chill the air in order to keep it at a specific temperature, which can be pre-defined by the user. Furthermore, most air-conditioning units also contain filters, which serve to remove airborne particulates from the air as it circulates. But how does it work? We’ll take a look momentarily, but before we do so, let’s first examine how it came to be.
The invention of the air conditioner
Air conditioning is more than a hundred years old. Its invention is widely credited to an electrical engineer called Willis Havilland Carrier, who worked for a Brooklyn-based publishing company. In the New York summers, the moisture levels inside the plant were high enough that the paper became unworkable using the printing techniques of the era.
Carrier’s solution was an ingenious one. He would have the air of the building blow across cooled pipes, and since cold air lacks the energy required to keep water molecules airborne, the moisture in the air went down. Like many inventors before him, Carrier had far exceeded the extent of his initial ambition. He had not simply invented a way of keeping paper cool, he had come up with a way of keeping any indoor environment comfortable. Before long, his invention had found its way into homes and businesses across the city and then the state and then beyond.
Air conditioning works, in principle, on a very similar principle to a fridge. It takes advantage of some simple principles and it does so through a number of mechanisms, which have been refined extensively since the technology’s first inception, but which still rely on blowing air over cooled pipes and thereby conducting heat away from one area and into another.
The first of these simple principles is that, when a liquid transitions into a gas, it absorbs heat. This principle, as one might imagine, has many practical applications. Air conditioners use this principle in order to evaporate and condense a special refrigerant substance while it is trapped within a series of coils. These substances are special in that they can transition between liquid and gas at very low temperatures, thereby keeping the required amount of heat and pressure to a minimum.
Through this closed system of coils, heat can migrate either from the interior of a building to the exterior (an arrangement through which the building would be cooled) or in the other direction, from the exterior to the interior (an arrangement through which the building would be heated).
Of course, it is one thing to transfer heat between coils, it is another to spread that effect over the entire internal volume of a room. For this we require another important component of the air conditioning system: the fan. Using a fan, the air of a room can be circulated over these cooled coils, and thereby the entirety of the room can be cooled. In sufficiently large and complex systems, this may be done using a series of vents and channels – of the sort action film stars frequently employ as hiding places.
The process does not end here; we still have another complicating factor to deal with. When the warm air of the room flows over the cold evaporator cools, the air is cooled. But also, the refrigerant inside the coils is heated. This causes it to transition from liquid to gas through evaporation. For the air conditioner to continue to function, this refrigerant must be returned to a liquid state again. If it did not, then it would be unable to properly flow through the pipes.
In order to do this, the refrigerant is compressed using a special device called – imaginatively enough – a compressor. This process causes unwanted heat – which is not desirous in a cooling system (though it may be in a heating system). This heat is channelled toward the exterior of a building through a dedicated fan and air vent system. The liquid can then be channelled back again and the cycle can begin anew.
Air conditioners thereby work in a large cycle, through which a liquid refrigerant cools an indoor environment and in doing so evaporates into a gas. It is then compressed back into a liquid again, and the resulting heat is channelled outside. Air conditioning, then, requires two distinct processes of cooling and compression in order to work.
What makes up an air conditioner?
In order to achieve the effects we have thus far narrated, an air conditioner must push the refrigerant in two directions – outside and then back inside. For this it needs four major components: the evaporator, whose role is to draw the liquid into the coils; the condenser, whose role is to transfer the liquid back into a liquid state; the compressor, whose role is to squeeze the refrigerant and the expansion valve, which regulates the flow of refrigerant back into the evaporator.
The evaporator constitutes the ‘cold side’ of the air conditioning system, along with a fan which blows the air of the room over the freezing coils. It is here that the refrigerant cools the air within the building and in doing so transitions to a gaseous state. The ‘hot side’ is a little more complicated, and comprises the compressor and condenser, along with another fan which moves the heat away from the coil. The compressor is actually a large electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a liquid.
The expansion valve is somewhere between these two sets of coils which enables the refrigerant to move between them in a controlled fashion. It does this by limiting the amount of compressed liquid moving to the evaporator and thereby absorbing any shocks which might result from changes in temperature.
As well as these four main components, most modern air conditioner systems include a variety of other gadgets which support and augment their functionality. These might include timers and thermostats, which can play a vital role in minimising the energy cost, and subsequent environmental impact, of an air conditioning system. The most cutting-edge air conditioning systems will even allow themselves to be controlled and monitored remotely using a mobile phone, which will allow large business operators to see exactly how their resources are being used.
The different sorts of air conditioners
Air conditioners come in all manner of shapes and sizes. Thus far, we have examined an architecture which is common to the vast majority of air conditioning systems. That said, there are a few designs different enough from what we’ve looked at thus far that they warrant special mention.
The smallest varieties of air conditioner are typically window air conditioners. These include all of the components we’ve looked at so far, but they include inside them a special box which can be fixed to the opening of a window. They will vent hot air from the rear and release cool air from the front. Obviously, these smaller offerings are the cheapest sort – and the most practicable in limited spaces – but they are also among the least efficient. Those looking to condition a large space will want to look to a larger solution.
When the system is a little larger, the design tends to become more modular – and thereby more efficient. The thermostat which controls the air conditioner will, in most cases, be shared with the heating system of the home – after all, you don’t want to have the two systems working at crossed purposes with one another. The compressor and condenser will typically be placed in a different unit, which is mounted onto the exterior of the building – in order to prevent the heat from interfering with the rest of the system. In the case of large buildings, these components are often mounted onto the roof – which is concealed from sight and therefore not liable to affect the aesthetics of the building.