Different Types of Air Conditioning Units
The air conditioning system is one of the most popular inventions of the last hundred years. It can be found in almost every indoor environment especially in very hot places, from the smallest of cars to the most enormous of cinema complexes. They have become widespread even in temperate climates, such as the United Kingdom, while in Gulf States, where the temperatures are more extreme, they have become almost indispensable.
But what are the differences between the varying types of air conditioner? In this article, we’ll briefly examine them.
How does an air conditioner work?
Before we can compare different types of air conditioners, we should familiarise ourselves with what an air-conditioning system actually does. Traditionally, an air-conditioning system combines a few basic scientific principles with some clever engineering in order to funnel heat away from one location and toward another. Let’s take a brief look at the traditional method of doing this common to most air-conditioning systems.
The evaporator coil is a section of coiled piping through which a fluid known as a refrigerant, which evaporates at very low temperatures, is pumped. By blowing air over these piping, an air conditioner can cool an indoor environment. This air will also cause the refrigerant to evaporate and thereby flow quickly through the piping to a special device called a compressor.
The role of the compressor is to squeeze the gas so that it reverts back into a liquid state. In doing this, the refrigerant will release heat. This heat is lost as the refrigerant flows through a second set of coils, known as the condenser coils. By blowing air over these coils with a fan, the system can disperse this heat away from the coils and into the surrounding air.
Finally, the newly cooled refrigerant passes through a valve which forces it back toward the evaporator coils, where it can cool the room again. This cycle perpetuates, channelling heat from the interior of a building to the exterior and thereby the interior is cooled.
That said, the heat can also flow in the opposite direction by simply rearranging the valve and compressor. Many modern air conditioning systems can thereby double as a heating system. On top of everything, since cool air is less capable of carrying moisture, the air conditioning system will also serve as a dehumidifier.
Every air conditioning system comprises all four of these items and uses them to transfer heat from the outside to the inside and vice versa. Not all air conditioning systems are created equally, however. Some, for example, might employ timers and thermostats in order to more closely regulate the temperature of an indoor environment and thereby ensure that is cooled as efficiently as possible.
Traditional air conditioning systems
The most obvious distinction between different varieties of air conditioners is the form in which they are packaged. Smaller units offer comparatively limited functionality at a much reduced cost, while larger ones offer much improved functionality
Window air conditioners
A window air conditioner is the smaller variety. It comprises an entire air conditioning system, packed into a space small enough that it can fit within a window frame. Since almost every sort of building already has a window frame available, air conditioner manufacturers are provided with a simple means of channelling heat to the exterior of the building.
Of course, an all-in-one solution like this has its problems. An air conditioner, almost by definition, has components which are hot and cold. If these components are too close together, then they begin to interfere with one another – heat from the latter makes the job of the former a great deal more difficult, and energy is required to offset this interference. As a consequence, smaller systems are less efficient.
Split-system air conditioning
A better solution is to have the two sets of coils in different units, spaced far apart from one another. In most cases, the condenser coils are placed on the exterior of the building – in especially large buildings, this might be on the roof.
Furthermore, a larger split-system air conditioner might employ a system of air-vents in order to channel cold air through a large building. This requires a great deal less energy per volume of air conditioned. For example, a building such as a hospital might contain hundreds of rooms. If each of them were to contain a window-ac unit, then a huge amount of energy might be consumed relative to a central air-conditioning system, which channels all of the heat in the building toward a dedicated condenser coil and fan system.
In especially massive buildings – and particularly those which extend upward across multiple stories, this becomes impracticable for a number of reasons. One problem stems from the distance limitations of the refrigerant piping; if the pipe is too long, then the compressor will begin to encounter problems with lubrication. Another is that the length of air ducts becomes unmanageable. Fortunately, there are alternative solutions at hand in the form of a chilled-water system.
As we have seen, standard architectures of air conditioners, while very popular, can encounter problems in sufficiently large buildings like office complexes and hotels. For this reason, such buildings sometimes employ alternative designs.
Chilled water systems
These systems rely on a single air conditioning unit on the exterior of the building, which refrigerates water to around five or six degrees Celsius – around the temperature of the inside of a fridge – and then pumps it through a network of pipes which extend throughout the building, connecting to a series of air handlers which transfer the cold to the surrounding air.
Cooling tower technology
A traditional air conditioning system uses a fan to dissipate the heat of the compressor coils. A far more effective means of achieving this can be brought about by running a stream of cold water over the coils.
The tower works by blowing air through a stream of water, which causes some of it evaporate. The water is thereby cooled. Obviously, this causes a problem in that the water supply is constantly diminishing thanks to this evaporation, and must therefore be replenished constantly. Furthermore, the efficacy of a water cooling tower is influenced by the humidity and pressure of the surrounding air.
Because of these problems, many larger businesses are turning to new technologies in order to reduce the cost of cooling their premises.
Off-peak cooling system
One particularly ingenious cooling system relies on the fact that energy is cheaper during the night-time, as the demand for it is lower. An off-peak cooling system exploits this by freezing a large volume of water during the night, and then using it to chill the interior of a building during the daytime. This approach reduces the strain on the grid, as well as minimising the impact of a cooling system, on both the finances of those that fund it, and the environment.
Geo-thermal heating is another option. It relies on the natural differences in temperature between the surface of the earth and a few feet underground it. While the temperature of the former might fluctuate, the latter will remain relatively constant. A geo-thermal heating system will exploit this by threading a network of pipes through both the walls of a building and the ground beneath them. By channelling water through these pipes, heat can be transferred from the building to the ground in the summer and from the ground to the building in the winter. This helps to stabilise the temperature of the building.
Measuring the efficacy of air conditioners
When deciding which air conditioner to buy, we must consider their capacity to cool and heat the air. This is typically measured using British Thermal Units (BTU); Air-conditioner retailers will typically list the power of their wares using this measure.
But what exactly is a BTU? Well, simply put, it is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit (one should be careful not to confuse it with a calorie, which is the amount of energy required to heat one gram of water by one degree Celsius). One BTU is equivalent to just over a thousand joules. Window air conditioners are typically rated at just over 10,000 BTU, while split-system ones can be many times that.
Of course, this does not tell us anything about its efficiency – which is perhaps a better measure of overall quality over the long term. To find the Energy Efficiency Rating (or EER) of an air conditioner, you must divide its BTU rating by its wattage. More efficient air conditioning systems are almost always more expensive. Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.
If you are considering buying an air-conditioning system, you must consider a range of factors before you can determine whether a more efficient air conditioner would be worthwhile. These might include the temperatures in the area (which would inform how often the system is activated) and the cost of energy per kilowatt-hour (kWh).