If you’re looking for an air conditioner for a home or workplace, then the decision can be a difficult one. With such a bewildering array of options available, it can be tricky to determine exactly which most closely suits your needs. In this article, we’ll attempt to make sense of what’s available, and to see exactly which sort of air conditioner suits which sort of setting.
How does air conditioning work?
Before we discuss these options, however, it’s worth first considering what it is that an air-conditioning system does. An air conditioning system is able to transfer heat from one location to another, using just a few basic scientific principles and some ingenious engineering. While there are many different models, most are designed in much the same way.
Put simply, an air-conditioning system comprises a loop of piping, through which flows a special liquid called the refrigerant. This liquid is designed to evaporate at very low temperatures, allowing it to flow quickly through the piping.
At two points in the circuit, the piping forms coils. The first set of coils are known as the evaporator coils, the second as the condenser coils. The former is placed on the inside of a building, while the latter are placed on the outside.
A fan blows air over the evaporator coils, distributing cold across the room and warming the refrigerant up so that it evaporates, and flows through the network until it reaches a compressor, which squeezes the refrigerant back into its liquid state, causing it to release heat into the evaporator coils. This heat is then dispersed using a second set of fans. The refrigerant then passes through a valve back to the evaporator coils, and the cycle begins again.
Air conditioners can do more than just cool an indoor environment. By reversing the direction of the valve, the system can channel heat in the opposite direction. Modern air conditioners exploit this, and are able to act as heaters. Moreover, since cool air is capable of carrying less moisture, the cooling action of an air conditioner can also have a dehumidifying effect.
Some air conditioners employ extra devices on top of this basic set, in order to achieve greater functionality. These might include timers and thermostats, which help to automate the system and thereby save time and money.
What are the different options available?
As we’ve mentioned, there are a myriad of different designs of air conditioner. But broadly speaking, all of this variety can be lumped into three categories. Once you understand them, it should be fairly obvious which of the three best suits your needs.
As we’ve seen, an air-conditioning system requires two coils, in order to distribute heat at one end of the refrigerant loop, and to collect it at the other.
For smaller environments with only modest air-conditioning needs, it’s possible to include both of these components, the piping which connects them, the fans, compressors and valves, in a single, self-contained unit. This unit is often mounted into a window, so that one side can be on the outside of a building and the other on the inside.
Naturally, these smaller units are not as efficient as their larger counterparts, as the two radiators must be placed in close proximity to one another. That said, they are also far cheaper, and so represent an attractive solution for those looking to air condition small spaces.
In a split system, the evaporator and condenser coils are placed further from each other – in separate units on the inside and outside of a building. This allows for much more power and efficiency, as the units can be larger, and the two sets of coils will not inadvertently interfere with one another. Split systems come in two different varieties – single-split system and multi-split systems.
A single-split system is one comprising two units, each containing a set of coils. Single-split systems make popular choices for small offices and server rooms, but they can also work in conjunction with one another to condition a larger space. Single-split systems are often cheaper than their larger, more elaborate counterparts. They’re also able to work independently of one another, and so if the air conditioning breaks in one room, the others will remain unaffected.
On the other hand, you’ll need enough space outdoors to accommodate an outdoor unit for every room you intend to condition. If you’re looking at conditioning many rooms, multi-split system is often preferable.
Multi-split systems work in the same way as their single-split cousins, except that they allow many different indoor units to be connected to a single outdoor one.
Multi-split systems have a distinct advantage in that they don’t require the exterior of a building to be covered with unsightly grey cubes. If you’re looking to preserve the appearance of your building, then a multi-split system can offer a solution. Another advantage of the multi-split system is its modularity – you can add many different sorts of internal unit to the system at the same time; including both ceiling and wall-mounted units.
Multi-split systems are a great deal more complex to install, and require air vents and coolant piping to be threaded throughout a building. They’re suited to larger buildings like hospitals and leisure centres, which have been designed to accommodate this sort of air conditioning system.
Thus far, the systems we’ve discussed assume that refrigerant is pumped at a fixed rate. Changes in temperature on the inside of a building are achieved by manipulating the speed of the fans on both sets of coils.
However, many newer air conditioning systems allow the use to change the flow of refrigerant through the system. These can be described as either VRF (variable refrigerant flow) or VRV (variable refrigerant volume). Though both of these terms essentially describe the same thing, the latter term is owned by Daikin, and so other manufacturers use the former.
However they’re described, these systems are far more efficient than their forebears, and are much more efficient and easier to control. VRF systems can be either heat pump or heat recovery. Heat pump is best for open-plan buildings, as it can provide either heat or cooling; heat recovery systems are great for large buildings with many rooms, as they’re capable of taking unwanted heat from one part of the system and transporting it to another, thereby minimising waste.
How do I know how powerful an air conditioning system is?
Now that we’ve seen the various different sorts of air conditioner, and decided which would best suit our purposes, we’re still left with an enormous amount of choice. How can we know which unit will offer the most power for the money?
The power of an air conditioner is most often measured in British Thermal Units. A single BTU refers to the amount of energy required to heat one pound of water by one degree Fahrenheit. (It’s a similar measure to the calorie, whose formula instead uses a gram of water and one degree Celsius, and therefore arrives at a completely different figure.)
If you’re looking at a single, window-mounted air conditioning unit, then you can expect to see ratings of more than ten-thousand BTUs. Split-system conditioners are able to achieve ratings which outstrip that by several orders of magnitude.
The British Thermal Unit is the measure by which AC retailers tout the power of their wares. If you can’t find the efficiency rating of a unit in its marketing material, then it’s safe to assume that the unit isn’t particularly impressive.
But an air-conditioning unit’s raw power tells us nothing about its efficiency. To find this, we need to divide the BTU rating of a conditioner by its wattage. This will give us an Energy Efficiency Rating which we can use to compare units of different wattages. The efficiency of a unit might justify a higher price-tag, particularly if it will be running often and at a high level. Account for the temperatures in the area, and the cost of energy, and you’ll be able to determine just how efficient a unit you need, and what outlay such a unit would justify.
Of course, the optimum temperature for a room is highly subjective. One person might feel too hot in a space where another might feel too cold. It’s therefore impossible to know for certain which unit will be best based purely on an objective measurement like BTUs.
But buying, shipping and installing a unit is an expensive and time-consuming business. It’s therefore wise to opt for an air conditioner which is slightly too powerful for your needs, in order to give yourself a little wiggle-room. This will minimise the possibility that you need to send the unit back. After all, a powerful unit can always be turned down!